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Finger-Higgens R, Hoover DL, Knight AC, Wilson SL, Bishop TBB, Reibold R, Reed SC, Duniway MC. Seasonal drought treatments impact plant and microbial uptake of nitrogen in a mixed shrub grassland on the Colorado Plateau. Ecology 2024; 105:e4393. [PMID: 39104160 DOI: 10.1002/ecy.4393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2024] [Accepted: 05/24/2024] [Indexed: 08/07/2024]
Abstract
For many drylands, both long- and short-term drought conditions can accentuate landscape heterogeneity at both temporal (e.g., role of seasonal patterns) and spatial (e.g., patchy plant cover) scales. Furthermore, short-term drought conditions occurring over one season can exacerbate long-term, multidecadal droughts or aridification, by limiting soil water recharge, decreasing plant growth, and altering biogeochemical cycles. Here, we examine how experimentally altered seasonal precipitation regimes in a mixed shrub grassland on the Colorado Plateau impact soil moisture, vegetation, and carbon and nitrogen cycling. The experiment was conducted from 2015 to 2019, during a regional multidecadal drought event, and consisted of three precipitation treatments, which were implemented with removable drought shelters intercepting ~66% of incoming precipitation including: control (ambient precipitation conditions, no shelter), warm season drought (sheltered April-October), and cool season drought (sheltered November-March). To track changes in vegetation, we measured biomass of the dominant shrub, Ephedra viridis, and estimated perennial plant and ground cover in the spring and the fall. Soil moisture dynamics suggested that warm season experimental drought had longer and more consistent drought legacy effects (occurring two out of the four drought cycles) than either cool season drought or ambient conditions, even during the driest years. We also found that E. viridis biomass remained consistent across treatments, while bunchgrass cover declined by 25% by 2019 across all treatments, with the earliest declines noticeable in the warm season drought plots. Extractable dissolved inorganic nitrogen and microbial biomass nitrogen concentrations appeared sensitive to seasonal drought conditions, with dissolved inorganic nitrogen increasing and microbial biomass nitrogen decreasing with reduced soil volumetric water content. Carbon stocks were not sensitive to drought but were greater under E. viridis patches. Additionally, we found that under E. viridis, there was a negative relationship between dissolved inorganic nitrogen and microbial biomass nitrogen, suggesting that drought-induced increases in dissolved inorganic nitrogen may be due to declines in nitrogen uptake from microbes and plants alike. This work suggests that perennial grass plant-soil feedbacks are more vulnerable to both short-term (seasonal) and long-term (multiyear) drought events than shrubs, which can impact the future trajectory of dryland mixed shrub grassland ecosystems as drought frequency and intensity will likely continue to increase with ongoing climate change.
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Affiliation(s)
| | - David L Hoover
- USDA-ARS Rangeland Resource and Systems Research Unit, Crops Research Laboratory, Fort Collins, Colorado, USA
| | - Anna C Knight
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
| | - Savannah L Wilson
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
| | - Tara B B Bishop
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
- Department of Earth Science, Utah Valley University, Orem, Utah, USA
| | - Robin Reibold
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
| | - Sasha C Reed
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
| | - Michael C Duniway
- US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA
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2
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Ding J, Eldridge DJ. Woody encroachment: social-ecological impacts and sustainable management. Biol Rev Camb Philos Soc 2024. [PMID: 38961449 DOI: 10.1111/brv.13104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 05/15/2024] [Accepted: 05/20/2024] [Indexed: 07/05/2024]
Abstract
Woody plants are encroaching across terrestrial ecosystems globally, and this has dramatic effects on how these systems function and the livelihoods of producers who rely on the land to support livestock production. Consequently, the removal of woody plants is promoted widely in the belief that it will reinstate former grasslands or open savanna. Despite this popular management approach to encroachment, we still have a relatively poor understanding of the effects of removal on society, and of alternative management practices that could balance the competing needs of pastoral production, biodiversity conservation and cultural values. This information is essential for maintaining both ecological and societal benefits in encroached systems under predicted future climate changes. In this review, we provide a comprehensive synthesis of the social-ecological perspectives of woody encroachment based on recent studies and global meta-analyses by assessing the ecological impacts of encroachment and its effects on sustainable development goals (SDGs) when woody plants are retained and when they are removed. We propose a working definition of woody encroachment based on species- and community-level characteristics; such a definition is needed to evaluate accurately the effects of encroachment. We show that encroachment is a natural process of succession rather than a sign of degradation, with encroachment resulting in an overall 8% increase in ecosystem multifunctionality. Removing woody plants can increase herbaceous plant richness, biomass and cover, but at the expense of biocrust cover. The effectiveness of woody plant removal depends on plant identity, and where, when and how they are removed. Under current management practices, either removal or retention of woody plants can induce trade-offs among ecosystem services, with no management practice maximising all SDGs [e.g. SDG2 (end hunger), SDG13 (climate change), SDG 15 (combat desertification)]. Given that encroachment of woody plants is likely to increase under future predicted hotter and drier climates, alternative management options such as carbon farming and ecotourism could be effective land uses for areas affected by encroachment.
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Affiliation(s)
- Jingyi Ding
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, No. 19, Xinjiekouwai Street, Haidian District, Beijing, 100875, China
| | - David J Eldridge
- Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences, University of New South Wales, High Street, Kensington, Sydney, 2052, New South Wales, Australia
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3
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Londe DW, Davis CA, Loss SR, Robertson EP, Haukos DA, Hovick TJ. Climate change causes declines and greater extremes in wetland inundation in a region important for wetland birds. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2024; 34:e2930. [PMID: 37941497 DOI: 10.1002/eap.2930] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 06/27/2023] [Accepted: 09/15/2023] [Indexed: 11/10/2023]
Abstract
Wetland ecosystems are vital for maintaining global biodiversity, as they provide important stopover sites for many species of migrating wetland-associated birds. However, because weather determines their hydrologic cycles, wetlands are highly vulnerable to effects of climate change. Although changes in temperature and precipitation resulting from climate change are expected to reduce inundation of wetlands, few efforts have been made to quantify how these changes will influence the availability of stopover sites for migratory wetland birds. Additionally, few studies have evaluated how climate change will influence interannual variability or the frequency of extremes in wetland availability. For spring and fall bird migration in seven ecoregions in the south-central Great Plains of North America, we developed predictive models associating abundance of inundated wetlands with a suite of weather and land cover variables. We then used these models to generate predictions of wetland inundation at the end of the century (2069-2099) under future climate change scenarios. Climate models predicted the average number of inundated wetlands will likely decline during both spring and fall migration periods, with declines being greatest in the eastern ecoregions of the southern Great Plains. However, the magnitude of predicted declines varied considerably across climate models and ecoregions, with uncertainty among climate models being greatest in the High Plains ecoregion. Most ecoregions also were predicted to experience more-frequent extremely dry years (i.e., years with extremely low wetland abundances), but the projected change in interannual variability of wetland inundation was relatively small and varied across ecoregions and seasons. Because the south-central Great Plains represents an important link along the migratory routes of many wetland-dependent avian species, future declines in wetland inundation and more frequent periods of only a few wetlands being inundated will result in an uncertain future for migratory birds as they experience reduced availability of wetland stopover habitat across their migration pathways.
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Affiliation(s)
- David W Londe
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Craig A Davis
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Scott R Loss
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Ellen P Robertson
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - David A Haukos
- U.S. Geological Survey, Kansas Cooperative Fish and Wildlife Research Unit, Kansas State University, Manhattan, Kansas, USA
| | - Torre J Hovick
- School of Natural Resource Sciences, North Dakota State University, Fargo, North Dakota, USA
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Niu F, Pierce NA, Okin GS, Archer SR, Fischella MR, Nadoum S. Sandblasting promotes shrub encroachment in arid grasslands. THE NEW PHYTOLOGIST 2023; 240:1817-1829. [PMID: 37658674 DOI: 10.1111/nph.19238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Accepted: 08/15/2023] [Indexed: 09/03/2023]
Abstract
Shrub encroachment is a common ecological state transition in global drylands and has myriad adverse effects on grasslands and the services they provide. This physiognomic shift is often ascribed to changes in climate (e.g. precipitation) and disturbance regimes (e.g. grazing and fire), but this remains debated. Aeolian processes are known to impact resource distribution in drylands, but their potential role in grassland-to-shrubland state changes has received little attention. We quantified the effects of 'sandblasting' (abrasive damage by wind-blown soil) on the ecophysiology of dryland grass vs shrub functional types using a portable wind tunnel to test the hypothesis that grasses would be more susceptible to sandblasting than shrubs and, thus, reinforce transitions to shrub dominance in wind-erodible grasslands when climate- or disturbance-induced reductions in ground cover occur. Grasses and shrubs responded differently to sandblasting, wherein water-use efficiency declined substantially in grasses, but only slightly in shrubs, owing to grasses having greater increases in day/nighttime leaf conductance and transpiration. The differential ecophysiological response to sandblasting exhibited by grass and shrub functional types could consequently alter the vegetation dynamics in dryland grasslands in favour of the xerophytic shrubs. Sandblasting could thus be an overlooked driver of shrub encroachment in wind-erodible grasslands.
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Affiliation(s)
- Furong Niu
- College of Forestry, Gansu Agricultural University, Lanzhou, Gansu, 730070, China
- School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85721, USA
| | - Nathan A Pierce
- USDA-Agricultural Research Service, Southwest Watershed Research Center, Tucson, AZ, 85719, USA
| | - Gregory S Okin
- Department of Geography, University of California, Los Angeles, CA, 90095, USA
| | - Steven R Archer
- School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85721, USA
| | - Michael R Fischella
- Department of Geography, University of California, Los Angeles, CA, 90095, USA
| | - Shereen Nadoum
- Department of Geography, University of California, Los Angeles, CA, 90095, USA
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5
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Brown RF, Collins SL. As above, not so below: Long-term dynamics of net primary production across a dryland transition zone. GLOBAL CHANGE BIOLOGY 2023; 29:3941-3953. [PMID: 37095743 DOI: 10.1111/gcb.16744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Accepted: 03/26/2023] [Indexed: 05/03/2023]
Abstract
Drylands are key contributors to interannual variation in the terrestrial carbon sink, which has been attributed primarily to broad-scale climatic anomalies that disproportionately affect net primary production (NPP) in these ecosystems. Current knowledge around the patterns and controls of NPP is based largely on measurements of aboveground net primary production (ANPP), particularly in the context of altered precipitation regimes. Limited evidence suggests belowground net primary production (BNPP), a major input to the terrestrial carbon pool, may respond differently than ANPP to precipitation, as well as other drivers of environmental change, such as nitrogen deposition and fire. Yet long-term measurements of BNPP are rare, contributing to uncertainty in carbon cycle assessments. Here, we used 16 years of annual NPP measurements to investigate responses of ANPP and BNPP to several environmental change drivers across a grassland-shrubland transition zone in the northern Chihuahuan Desert. ANPP was positively correlated with annual precipitation across this landscape; however, this relationship was weaker within sites. BNPP, on the other hand, was weakly correlated with precipitation only in Chihuahuan Desert shrubland. Although NPP generally exhibited similar trends among sites, temporal correlations between ANPP and BNPP within sites were weak. We found chronic nitrogen enrichment stimulated ANPP, whereas a one-time prescribed burn reduced ANPP for nearly a decade. Surprisingly, BNPP was largely unaffected by these factors. Together, our results suggest that BNPP is driven by a different set of controls than ANPP. Furthermore, our findings imply belowground production cannot be inferred from aboveground measurements in dryland ecosystems. Improving understanding around the patterns and controls of dryland NPP at interannual to decadal scales is fundamentally important because of their measurable impact on the global carbon cycle. This study underscores the need for more long-term measurements of BNPP to improve assessments of the terrestrial carbon sink, particularly in the context of ongoing environmental change.
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Affiliation(s)
- Renée F Brown
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA
| | - Scott L Collins
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA
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6
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Yang X, Xiao X, Zhang C. Spatiotemporal variability and key factors of evergreen forest encroachment in the southern Great Plains. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2023; 329:117012. [PMID: 36608618 DOI: 10.1016/j.jenvman.2022.117012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Revised: 10/30/2022] [Accepted: 12/08/2022] [Indexed: 06/17/2023]
Abstract
Woody plant encroachment has been long observed in the southern Great Plains (SGP) of the United States. However, our understanding of its spatiotemporal variability, which is the basis for informed and targeted management strategy, is still poor. This study investigates the encroachment of evergreen forest, which is the most important encroachment component in the SGP. A validated evergreen forest map of the SGP (30 m resolution, for the time period 2015 to 2017) from our previous study was utilized (referred to as evergreen_base). Sample plots of evergreen forest (as of 2017) were collected across the study area, based on which a threshold of winter season (January and February) mean normalized difference vegetation index (NDVIwinter) was derived for each of the 5 sub-regions, using Landsat 7 surface reflectance data from 2015 to 2017. Then a NDVIwinter layer was created for each year within the four time periods of 1985-1989, 1995-1999, 2005-2009, and 2015-2017, with winter season surface reflectance data from Landsat 4, 5, and 7. By applying the sub-region specific NDVIwinter thresholds to the annual NDVIwinter layers and the evergreen_base, a SGP evergreen forest map was generated for each of those years. The annual evergreen forest maps within each time period were composited into one. According to the resulting four composite evergreen forest maps, mean annual encroachment rate (km2/year) was calculated at sub-region and ecoregion scales, over each of the three temporal stages 1990-1999, 2000-2009, and 2010-2017, respectively. To understand the spatiotemporal variability of the encroachment, the encroachment rate at each temporal stage was related to the corresponding initial evergreen forest area, mean annual precipitation (MAP), and mean annual burned area (MABA) through linear regression and pairwise comparison. Results suggest that most of the ecoregions have seen a slowing trend of evergreen forest encroachment since 1990. The temporal trend of encroachment rate tends to be consistent with that of MAP, but opposite to that of MABA. The spatial variability of the encroachment rate among ecoregions can be largely (>68%) explained by initial evergreen forest area but shows no significant relationship with MAP or MABA. These findings provide pertinent guidance for the combat of woody plant encroachment in the SGP under the context of climate change.
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Affiliation(s)
- Xuebin Yang
- Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, 73019, USA; Department of Geography and the Environment, Syracuse University, Syracuse, NY, 13244, USA.
| | - Xiangming Xiao
- Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, 73019, USA
| | - Chenchen Zhang
- Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, 73019, USA
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7
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Liu Y, Cheng J, Schmid B, Sheng J. Aridity shifts the difference in carbon uptake and storage between wooded and pure grasslands from positive to negative. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 861:160614. [PMID: 36460107 DOI: 10.1016/j.scitotenv.2022.160614] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 11/24/2022] [Accepted: 11/27/2022] [Indexed: 06/17/2023]
Abstract
Woody plant encroachment in arid grasslands may reduce plant uptake and soil storage of carbon (C) with consequences for the global C cycle, yet multi-site comparative studies have not been done so far and experiments are not feasible due to the long time needed for soil organic C (SOC) to accumulate. We selected multiple grassland sites with ≥50 % or 0 % woody plant aboveground biomass in each of six vegetation types representing a gradient of increasing aridity, resulting in a comparative study design with a total of 178 pure and 106 wooded grasslands distributed over the large geographic area of Xinjiang, China. Differences between wooded and pure grasslands in SOC stocks in the top 100 cm of the soil changed from positive to negative with increasing aridity. This effect was strongest in the upper soil layers, suggesting that woody plants had perhaps not been present for long enough to leave a signal in the lower soil layers. The differences in SOC stocks were related to differences in plant belowground standing C (BGC) and these to differences in yearly plant aboveground C uptake (ANPP) between wooded and pure grasslands. At more arid sites, wooded grasslands had lower ANPP and BGC because of reduced contributions of herbaceous plants that were not fully compensated by woody plants. Considering predicted increases in aridity in the study region, our results suggest that to avoid future losses of grassland SOC stocks - which are several ten times higher than the C stored in plant organs - management should try to prevent or reduce woody plant encroachment.
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Affiliation(s)
- Yunhua Liu
- Xinjiang Key Laboratory of Soil and Plant Ecological Processes, College of Recourses and Environment, Xinjiang Agricultural University, Urumqi 830052, China
| | - Junhui Cheng
- Xinjiang Key Laboratory of Soil and Plant Ecological Processes, College of Recourses and Environment, Xinjiang Agricultural University, Urumqi 830052, China
| | - Bernhard Schmid
- Remote Sensing Laboratories, Department of Geography, University of Zürich, Zürich, Switzerland.
| | - Jiandong Sheng
- Xinjiang Key Laboratory of Soil and Plant Ecological Processes, College of Recourses and Environment, Xinjiang Agricultural University, Urumqi 830052, China.
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8
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Bennion LD, Ward D. Plant-soil feedback from eastern redcedar ( Juniperus virginiana) inhibits the growth of grasses in encroaching range. Ecol Evol 2022; 12:e9400. [PMID: 36311395 PMCID: PMC9596334 DOI: 10.1002/ece3.9400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2022] [Revised: 09/05/2022] [Accepted: 09/20/2022] [Indexed: 11/22/2022] Open
Abstract
The encroachment of woody plants into grasslands is an ongoing global problem that is largely attributed to anthropogenic factors such as climate change and land management practices. Determining the mechanisms that drive successful encroachment is a critical step towards planning restoration and long-term management strategies. Feedbacks between soil and aboveground communities can have a large influence on the fitness of plants and must be considered as potentially important drivers for woody encroachment. We conducted a plant-soil feedback experiment in a greenhouse between eastern redcedar Juniperus virginiana and four common North American prairie grass species. We assessed how soils that had been occupied by redcedar, a pervasive woody encroacher in the Great Plains of North America, affected the growth of Andropogon gerardi, Schizachyrium scoparium, Bromus inermis, and Pascopyrum smithii over time. We evaluated the effect of redcedar on grass performance by comparing the height and biomass of individuals that were grown in live or sterilized conspecific or redcedar soil. We found redcedar created a negative plant-soil feedback that limited the growth of the cool season grasses B. inermis and P. smithii, reducing their overall biomass by >60%. These effects were found in both live and sterilized redcedar soils. In live soils, some growth suppression can be attributed to the negative effects of soil microbes. The limitation of grass growth in sterile soils indicates redcedar may exude an allelochemical into the soil that limits grass growth. Our results demonstrate that plant-soil feedback created by redcedar inhibits the growth of certain grass species. By creating a plant-plant interaction that negatively affects competitors, redcedars increase the probability of seedling survival until they can grow to overtop their neighbors. These results indicate plant-soil feedback is a mechanism of native woody plant encroachment which could be important in many systems yet is understudied.
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Affiliation(s)
| | - David Ward
- Department of Biological SciencesKent State UniversityKentOhioUSA
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9
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The Spatiotemporal Response of Vegetation Changes to Precipitation and Soil Moisture in Drylands in the North Temperate Mid-Latitudes. REMOTE SENSING 2022. [DOI: 10.3390/rs14153511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Vegetation growth in drylands is highly constrained by water availability. How dryland vegetation responds to changes in precipitation and soil moisture in the context of a warming climate is not well understood. In this study, warm drylands in the temperate zone between 30 and 50° N, including North America (NA), the Mediterranean region (MD), Central Asia (CA), and East Asia (EA), were selected as the study area. After verifying the trends and anomalies of three kinds of leaf area index (LAI) datasets (GLASS LAI, GLEAM LAI, and GLOBAMAP LAI) in the study area, we mainly used the climate (GPCC precipitation and ERA5 temperature), GLEAM soil moisture, and GLASS LAI datasets from 1981 to 2018 to analyze the response of vegetation growth to changes in precipitation and soil moisture. The results of the three mutually validated LAI datasets show an overall greening of dryland vegetation with the same increasing trend of 0.002 per year in LAI over the past 38 years. LAI and precipitation exhibited a strong correlation in the eastern part of the NA drylands and the northeastern part of the EA drylands. LAI and soil moisture exhibited a strong correlation in the eastern part of the NA drylands, the eastern part of the MD drylands, the southern part of the CA drylands, and the northeastern part of the EA drylands. The results of this study will contribute to the understanding of vegetation dynamics and their response to changing water conditions in the Northern Hemisphere midlatitude drylands.
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Dornbusch MJ, Limb RF, Bloom-Cornelius IV, Elmore RD, Weir JR, Fuhlendorf SD. Factors influencing the persistence of a fire-sensitive Artemisia species in a fire-dependent ecosystem. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2022; 32:e2604. [PMID: 35365937 DOI: 10.1002/eap.2604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 01/03/2022] [Accepted: 01/14/2022] [Indexed: 06/14/2023]
Abstract
Fire refugia and patchiness are important to the persistence of fire-sensitive species and may facilitate biodiversity conservation in fire-dependent landscapes. Playing the role of ecosystem engineers, large herbivores alter vegetation structure and can reduce wildfire risk. However, herbivore effects on the spatial variability of fire and the persistence of fire-sensitive species are not clear. To examine the hypothesis that large herbivores support the persistence of fire-sensitive species through the creation of fire refugia in fire-prone landscapes, we examined the response of a fire-sensitive plant, Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & Young]) to fire and grazing in the fire-dependent mixed-grass prairie of the northern Great Plains. We carried out a controlled burn in 2010 within pre-established exclosures that allowed differential access to wild and domestic herbivores and no record of fire in the previous 75 years due to fire suppression efforts. The experiment was set up with a split-plot design to also examine potential changes in plots that were not burned. Canopy cover of big sagebrush was recorded before the burn in 2010 and again in 2011 with percent area burned recorded within 1-month post-fire in the burned plots. Percentage area burned was the greatest in ungulate exclosures (92% ± 2%) and the least in open areas (55% ± 21%), suggesting that large herbivores influenced fire behavior (e.g., reducing fire intensity and rate of spread) and are likely to increase fire patchiness through their alterations to the fuel bed. Regression analysis indicated that the proportion of sagebrush cover lost was significantly correlated with the proportion of area burned (R2 = 0.76, p = 0.05). No differences in the non-burn plots were observed among grazing treatments or among years. Altogether, this illustrates the potential importance of large herbivores in creating biotic-driven fire refugia for fire-sensitive species to survive within the flammable fuel matrix of fire-dependent grassland ecosystems such as the mixed-grass prairie. Our findings also attest to the resiliency of the northern Great Plains to fire and herbivory and underscore the value of managing grasslands for heterogeneity with spatial and temporal variations in these historic disturbances.
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Affiliation(s)
- Megan J Dornbusch
- School of Natural Resource Sciences, North Dakota State University, Fargo, North Dakota, USA
| | - Ryan F Limb
- School of Natural Resource Sciences, North Dakota State University, Fargo, North Dakota, USA
| | - Ilana V Bloom-Cornelius
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - R Dwayne Elmore
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - John R Weir
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Samuel D Fuhlendorf
- Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA
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11
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Multi-Temporal LiDAR and Hyperspectral Data Fusion for Classification of Semi-Arid Woody Cover Species. REMOTE SENSING 2022. [DOI: 10.3390/rs14122896] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
Mapping the spatial distribution of woody vegetation is important for monitoring, managing, and studying woody encroachment in grasslands. However, in semi-arid regions, remotely sensed discrimination of tree species is difficult primarily due to the tree similarities, small and sparse canopy cover, but may also be due to overlapping woody canopies as well as seasonal leaf retention (deciduous versus evergreen) characteristics. Similar studies in different biomes have achieved low accuracies using coarse spatial resolution image data. The objective of this study was to investigate the use of multi-temporal, airborne hyperspectral imagery and light detection and ranging (LiDAR) derived data for tree species classification in a semi-arid desert region. This study produces highly accurate classifications by combining multi-temporal fine spatial resolution hyperspectral and LiDAR data (~1 m) through a reproducible scripting and machine learning approach that can be applied to larger areas and similar datasets. Combining multi-temporal vegetation indices and canopy height models led to an overall accuracy of 95.28% and kappa of 94.17%. Five woody species were discriminated resulting in producer accuracies ranging from 86.12% to 98.38%. The influence of fusing spectral and structural information in a random forest classifier for tree identification is evident. Additionally, a multi-temporal dataset slightly increases classification accuracies over a single data collection. Our results show a promising methodology for tree species classification in a semi-arid region using multi-temporal hyperspectral and LiDAR remote sensing data.
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12
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White JDM, Stevens N, Fisher JT, Archibald S, Reynolds C. Nature‐reliant, low‐income households face the highest rates of woody‐plant encroachment in South Africa. PEOPLE AND NATURE 2022. [DOI: 10.1002/pan3.10329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Affiliation(s)
- Joseph D. M. White
- School of Animal, Plant and Environmental Sciences University of the Witwatersrand, WITS Johannesburg South Africa
| | - Nicola Stevens
- School of Animal, Plant and Environmental Sciences University of the Witwatersrand, WITS Johannesburg South Africa
- Environmental Change Institute, School of Geography and the Environment University of Oxford Oxford UK
| | - Jolene T. Fisher
- School of Animal, Plant and Environmental Sciences University of the Witwatersrand, WITS Johannesburg South Africa
| | - Sally Archibald
- School of Animal, Plant and Environmental Sciences University of the Witwatersrand, WITS Johannesburg South Africa
| | - Chevonne Reynolds
- School of Animal, Plant and Environmental Sciences University of the Witwatersrand, WITS Johannesburg South Africa
- FitzPatrick Institute of African Ornithology, DST‐NRF Center of Excellence University of Cape Town Rondebosch South Africa
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13
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Response of Surface Runoff and Sediment to the Conversion of a Marginal Grassland to a Switchgrass (Panicum virgatum) Bioenergy Feedstock System. LAND 2022. [DOI: 10.3390/land11040540] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The land systems between the humid and arid zones around the globe are critical to agricultural production and are characterized by a strong integration of the land use and water dynamics. In the southern Great Plains (SGP) of the United States, lakes and farm ponds are essential components in the land systems, and they provide unique habitats for wildlife, and critical water resources for irrigation and municipal water supplies. The conversion of the marginal grasslands to switchgrass (Panicum virgatum) biofuel feedstock for energy production has been proposed in the region. However, we have limited experimental data to assess the impact of this potential land-use change on the surface runoff, which is the primary water source for surface impoundments. Here, we report the results from a paired experimental watershed study that compared the runoff and sediment responses that were related to the conversion of prairie to a low-input biomass production system. The results show no significant change in the relationship between the event-based runoff and the precipitation. There was a substantial increase in the sediment yield (328%) during the conversion phase that was associated with the switchgrass establishment (i.e., the site preparation, herbicide application, and switchgrass planting). Once the switchgrass was established, the sediment yield was 21% lower than the nonconverted watershed. Our site-specific observations suggest that switchgrass biofuel production systems will have a minimum impact on the existing land and water systems. It may potentially serve as an environmentally friendly and economically viable alternative land use for slowing woody encroachment on marginal lands in the SGP.
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Kelly Hoffman J, Kyle GT, Treadwell ML, Patrick Bixler R, Kreuter UP. A Process-Oriented Model of Decision-Making toward Landscape-Scale Prescribed Fire Implementation in the Southern Great Plains, USA. ENVIRONMENTAL MANAGEMENT 2021; 68:802-813. [PMID: 34545419 DOI: 10.1007/s00267-021-01538-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2021] [Accepted: 09/07/2021] [Indexed: 06/13/2023]
Abstract
In this investigation, we developed a model of the psychological drivers of landowners' decisions to implement prescribed fire on their properties. The Southern Great Plains in the USA evolved with fire and prescribed fire is an important management tool aimed at maintaining and enhancing ecological and economic resilience in the region. The conceptualized model is reflective of a decision-making paradigm that considers decision making to be a process inclusive of a variety of factors and their inter-relationships to arrive at judgments on whether or not to utilize prescribed fire. The approach considered a spectrum of inputs, obstacles, and their associations to capture the complexity of decision making that is often lost when modeling single factors in dynamic social-ecological settings. Further, we considered the decision to use prescribed fire as a multifactor process that incorporates not only individual barriers to fire implementation but inter-barrier associations and other inputs (e.g., sociodemographic variables). Path analysis revealed five statistically significant relationships within the hypothesized model. For prescribed fire decision making, women tended to be more analytical whereas men were more inclined to rely on heuristics. Additionally, those who indicated owning their property for non-consumptive recreation-related reasons were also more inclined to rely upon heuristics. Texans reported more experience with prescribed fire as did respondents who indicated owning property for livestock product. Alternately, those owning their property for an investment and non-consumptive recreation opportunities reported less experience with prescribed fire. Last, ownership for crop and livestock production was positively associated with past wildfire experience. Findings have implications for three issue areas: (1) the provision of an evolved conceptualization through which prescribed fire implementation decisions can be examined, (2) enhancing the approach of prescribed fire outreach to a changing landowner population, and (3) improving the content and delivery of prescribed fire education efforts.
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Affiliation(s)
- J Kelly Hoffman
- Department of Ecosystem Science and Management, Texas A&M University, Austin, TX, USA
| | - Gerard T Kyle
- Department of Rangeland, Wildlife & Fisheries Management, Texas A&M University, College Station, TX, 77843, USA.
| | - Morgan L Treadwell
- Department of Rangeland, Wildlife & Fisheries Management, Texas A&M AgriLife Extension Service, Texas A&M University, San Angelo, TX, 76901, USA
| | - R Patrick Bixler
- Lyndon B. Johnson School of Public Affairs, University of Texas, Austin, TX, 78712, USA
| | - Urs P Kreuter
- Department of Ecology & Conservation Biology, Texas A&M University, College Station, TX, 778473, USA
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15
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Felton AJ, Shriver RK, Bradford JB, Suding KN, Allred BW, Adler PB. Biotic vs abiotic controls on temporal sensitivity of primary production to precipitation across North American drylands. THE NEW PHYTOLOGIST 2021; 231:2150-2161. [PMID: 34105783 DOI: 10.1111/nph.17543] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 05/31/2021] [Indexed: 05/26/2023]
Abstract
Dryland net primary productivity (NPP) is sensitive to temporal variation in precipitation (PPT), but the magnitude of this 'temporal sensitivity' varies spatially. Hypotheses for spatial variation in temporal sensitivity have often emphasized abiotic factors, such as moisture limitation, while overlooking biotic factors, such as vegetation structure. We tested these hypotheses using spatiotemporal models fit to remote-sensing data sets to assess how vegetation structure and climate influence temporal sensitivity across five dryland ecoregions of the western USA. Temporal sensitivity was higher in locations and ecoregions dominated by herbaceous vegetation. By contrast, much less spatial variation in temporal sensitivity was explained by mean annual PPT. In fact, ecoregion-specific models showed inconsistent associations of sensitivity and PPT; whereas sensitivity decreased with increasing mean annual PPT in most ecoregions, it increased with mean annual PPT in the most arid ecoregion, the hot deserts. The strong, positive influence of herbaceous vegetation on temporal sensitivity indicates that herbaceous-dominated drylands will be particularly sensitive to future increases in precipitation variability and that dramatic changes in cover type caused by invasions or shrub encroachment will lead to changes in dryland NPP dynamics, perhaps independent of changes in precipitation.
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Affiliation(s)
- Andrew J Felton
- Department of Wildland Resources and The Ecology Center, Utah State University, Logan, UT, 84322, USA
| | - Robert K Shriver
- Department of Wildland Resources and The Ecology Center, Utah State University, Logan, UT, 84322, USA
- US Geological Survey, Southwest Biological Science Center, Flagstaff, AZ, 86001, USA
- Department of Natural Resources and Environmental Science, University of Nevada, Reno, Reno, NV, 89557, USA
| | - John B Bradford
- US Geological Survey, Southwest Biological Science Center, Flagstaff, AZ, 86001, USA
| | - Katharine N Suding
- Department of Ecology and Evolutionary Biology, Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, 80309, USA
| | - Brady W Allred
- W.A. Franke College of Forestry and Conservation, University of Montana, Missoula, MT, 59812, USA
| | - Peter B Adler
- Department of Wildland Resources and The Ecology Center, Utah State University, Logan, UT, 84322, USA
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16
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Fire and browsing interact to alter intra-clonal stem dynamics of an encroaching shrub in tallgrass prairie. Oecologia 2021; 196:1039-1048. [PMID: 34228246 DOI: 10.1007/s00442-021-04980-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 06/28/2021] [Indexed: 10/20/2022]
Abstract
The expansion of woody species into grasslands has altered community structure and ecosystem function of grasslands worldwide. In tallgrass prairie of the Central Great Plains, USA, decreased fire frequency and intensity have increased the cover and abundance of woody species. In particular, clonal shrub cover has increased at accelerated rates due to vegetative reproduction and resprouting after disturbance. We measured the intra-clonal stem demography and relative growth rates (estimated change in woody biomass) of the shrub Cornus drummondii in response to fire frequency (4 vs 20 year burn intervals) and simulated browsing during the 2018 and 2019 growing seasons at Konza Prairie Biological Station (Manhattan, Kansas). Overall, infrequent fire (4 year burn interval) increased intra-clonal stem relative growth rates and shrub relative growth rates. Intra-clonal stem relative growth rates were reduced in unbrowsed clones in 2018 due to drought and simulated browsing reduced intra-clonal stem relative growth rates in 2019. Additionally, simulated browsing nearly eliminated flower production within clones but did not affect intra-clonal stem mortality or recruitment within a growing season. Fire in conjunction with simulated browsing reduced estimated relative growth rates for entire shrub clones. Browsed shrubs that experienced prescribed fire in 2017 had reduced intra-clonal stem densities compared to unbrowsed shrubs and stem densities of browsed shrubs did not recover in 2018 or 2019. These results illustrate that infrequent fire alone promotes the expansion of clonal shrubs in tallgrass prairie and multiple interacting disturbances (e.g., fire and browsing) are required to control the spread of clonal shrubs into grasslands.
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17
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Nerlekar AN, Mehta N, Pokar R, Bhagwat M, Misher C, Joshi P, Hiremath AJ. Removal or utilization? Testing alternative approaches to the management of an invasive woody legume in an arid Indian grassland. Restor Ecol 2021. [DOI: 10.1111/rec.13477] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ashish N. Nerlekar
- Ashoka Trust for Research in Ecology and the Environment Bengaluru Karnataka 560064 India
- Present address: Department of Ecology and Conservation Biology Texas A&M University College Station TX 77843‐2258 U.S.A
| | - Nirav Mehta
- Ashoka Trust for Research in Ecology and the Environment Bengaluru Karnataka 560064 India
| | - Ritesh Pokar
- Sahjeevan Bhuj Gujarat 370001 India
- Department of Botany, Faculty of Science The M. S. University of Baroda Vadodara Gujarat 390002 India
| | - Mayur Bhagwat
- Ashoka Trust for Research in Ecology and the Environment Bengaluru Karnataka 560064 India
| | - Chetan Misher
- Ashoka Trust for Research in Ecology and the Environment Bengaluru Karnataka 560064 India
- Manipal Academy of Higher Education Manipal Karnataka 576104 India
| | | | - Ankila J. Hiremath
- Ashoka Trust for Research in Ecology and the Environment Bengaluru Karnataka 560064 India
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18
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Halpern CB, Antos JA. Rates, patterns, and drivers of tree reinvasion 15 years after large‐scale meadow‐restoration treatments. Restor Ecol 2021. [DOI: 10.1111/rec.13377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Charles B. Halpern
- School of Environmental and Forest Sciences, College of the Environment University of Washington Box 352100 Seattle WA 98195‐2100 U.S.A
| | - Joseph A. Antos
- Department of Biology University of Victoria PO Box 3020 Victoria British Columbia V8W 3N5 Canada
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19
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Consequences of Piñon-Juniper Woodland Fuel Reduction: Prescribed Fire Increases Soil Erosion While Mastication Does Not. Ecosystems 2021. [DOI: 10.1007/s10021-021-00644-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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20
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Zinnert JC, Nippert JB, Rudgers JA, Pennings SC, González G, Alber M, Baer SG, Blair JM, Burd A, Collins SL, Craft C, Di Iorio D, Dodds WK, Groffman PM, Herbert E, Hladik C, Li F, Litvak ME, Newsome S, O’Donnell J, Pockman WT, Schalles J, Young DR. State changes: insights from the U.S. Long Term Ecological Research Network. Ecosphere 2021. [DOI: 10.1002/ecs2.3433] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- Julie C. Zinnert
- Department of Biology Virginia Commonwealth University 1000 West Cary Street Richmond Virginia23284USA
| | - Jesse B. Nippert
- Division of Biology Kansas State University Manhattan Kansas66506USA
| | - Jennifer A. Rudgers
- Department of Biology University of New Mexico Albuquerque New Mexico87131USA
| | - Steven C. Pennings
- Department of Biology and Biochemistry University of Houston Houston Texas77204USA
| | - Grizelle González
- International Institute of Tropical Forestry United States Department of Agriculture, Forest Service Jardín Botánico Sur, 1201 Ceiba St.‐Río Piedras San Juan00926Puerto Rico
| | - Merryl Alber
- Department of Marine Sciences University of Georgia Athens Georgia30602USA
| | - Sara G. Baer
- Kansas Biological Survey and Department of Ecology and Evolutionary Biology University of Kansas Lawrence Kansas66047USA
| | - John M. Blair
- Division of Biology Kansas State University Manhattan Kansas66506USA
| | - Adrian Burd
- Department of Marine Sciences University of Georgia Athens Georgia30602USA
| | - Scott L. Collins
- Department of Biology University of New Mexico Albuquerque New Mexico87131USA
| | - Christopher Craft
- School of Public and Environmental Affairs Indiana University Bloomington Indiana47405USA
| | - Daniela Di Iorio
- Department of Marine Sciences University of Georgia Athens Georgia30602USA
| | - Walter K. Dodds
- Division of Biology Kansas State University Manhattan Kansas66506USA
| | - Peter M. Groffman
- City University of New York Advanced Science Research Center at the Graduate Center New York New York10031USA
- Cary Institute of Ecosystem Studies Millbrook New York12545USA
| | | | - Christine Hladik
- Department of Geology and Geography Georgia Southern University Statesboro Georgia30460USA
| | - Fan Li
- Department of Biology and Biochemistry University of Houston Houston Texas77204USA
| | - Marcy E. Litvak
- Department of Biology University of New Mexico Albuquerque New Mexico87131USA
| | - Seth Newsome
- Department of Biology University of New Mexico Albuquerque New Mexico87131USA
| | - John O’Donnell
- Department of Biology Creighton University Omaha Nebraska68178USA
| | - William T. Pockman
- Department of Biology University of New Mexico Albuquerque New Mexico87131USA
| | - John Schalles
- Department of Biology Creighton University Omaha Nebraska68178USA
| | - Donald R. Young
- Department of Biology Virginia Commonwealth University 1000 West Cary Street Richmond Virginia23284USA
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21
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Using UAV Imagery to Detect and Map Woody Species Encroachment in a Subalpine Grassland: Advantages and Limits. REMOTE SENSING 2021. [DOI: 10.3390/rs13071239] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Woody species encroachment on grassland ecosystems is occurring worldwide with both negative and positive consequences for biodiversity conservation and ecosystem services. Remote sensing and image analysis represent useful tools for the monitoring of this process. In this paper, we aimed at evaluating quantitatively the potential of using high-resolution UAV imagery to monitor the encroachment process during its early development and at comparing the performance of manual and semi-automatic classification methods. The RGB images of an abandoned subalpine grassland on the Western Italian Alps were acquired by drone and then classified through manual photo-interpretation, with both pixel- and object-based semi-automatic models, using machine-learning algorithms. The classification techniques were applied at different resolution levels and tested for their accuracy against reference data including measurements of tree dimensions collected in the field. Results showed that the most accurate method was the photo-interpretation (≈99%), followed by the pixel-based approach (≈86%) that was faster than the manual technique and more accurate than the object-based one (≈78%). The dimensional threshold for juvenile tree detection was lower for the photo-interpretation but comparable to the pixel-based one. Therefore, for the encroachment mapping at its early stages, the pixel-based approach proved to be a promising and pragmatic choice.
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22
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Freund SM, Newingham BA, Chambers JC, Urza AK, Roundy BA, Cushman JH. Plant functional groups and species contribute to ecological resilience a decade after woodland expansion treatments. Ecosphere 2021. [DOI: 10.1002/ecs2.3325] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Affiliation(s)
- Stephanie M. Freund
- Department of Natural Resources and Environmental Science University of Nevada, Reno Reno Nevada89557USA
| | - Beth A. Newingham
- Department of Natural Resources and Environmental Science University of Nevada, Reno Reno Nevada89557USA
- Great Basin Rangelands Research Unit USDA Agricultural Research Service Reno Nevada89512USA
| | | | - Alexandra K. Urza
- Rocky Mountain Research Station USDA Forest Service Reno Nevada89509USA
| | - Bruce A. Roundy
- Department of Plant and Wildlife Sciences Brigham Young University Provo Utah84602USA
| | - J. Hall Cushman
- Department of Natural Resources and Environmental Science University of Nevada, Reno Reno Nevada89557USA
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23
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Holdrege MC, Beard KH, Kulmatiski A. Woody plant growth increases with precipitation intensity in a cold semiarid system. Ecology 2020; 102:e03212. [PMID: 33001437 DOI: 10.1002/ecy.3212] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 07/17/2020] [Accepted: 08/17/2020] [Indexed: 11/07/2022]
Abstract
As the atmosphere warms, precipitation events become larger, but less frequent. Yet, there is fundamental disagreement about how increased precipitation intensity will affect vegetation. Walter's two-layer hypothesis and experiments testing it have demonstrated that precipitation intensity can increase woody plant growth. Observational studies have found the opposite pattern. Not only are the patterns contradictory, but inference is largely limited to grasslands and savannas. We tested the effects of increased precipitation intensity in a shrub-steppe ecosystem that receives >30% of its precipitation as snow. We used 11 (8 × 8 m) shelters to collect and redeposit rain and snow as larger, more intense events. Total annual precipitation was the same in all plots, but each plot received different precipitation event sizes ranging from 1 to 18 mm. Over three growing seasons, larger precipitation event sizes increased soil water availability, sagebrush (Artemisia tridentata) stem radius, and canopy greenness, decreased new root growth in shallow soils, and had no effect on herbaceous plant cover. Thus, we found that increased precipitation intensity can increase soil water availability and woody plant growth in a cold semiarid system. Assuming that stem growth is positively correlated with shrub reproduction, establishment and spread, results suggest that increasing precipitation intensity may have contributed to the woody plant encroachment observed around the world in the past 50 yr. Further, continuing increases in precipitation intensity caused by atmospheric warming are likely to continue to contribute to shrub encroachment in the future.
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Affiliation(s)
- Martin C Holdrege
- Department of Wildland Resources, Utah State University and the Ecology Center, Logan, Utah, 84322-5230, USA
| | - Karen H Beard
- Department of Wildland Resources, Utah State University and the Ecology Center, Logan, Utah, 84322-5230, USA
| | - Andrew Kulmatiski
- Department of Wildland Resources, Utah State University and the Ecology Center, Logan, Utah, 84322-5230, USA
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24
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Klemm T, Briske DD, Reeves MC. Potential natural vegetation and NPP responses to future climates in the U.S. Great Plains. Ecosphere 2020. [DOI: 10.1002/ecs2.3264] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Affiliation(s)
- Toni Klemm
- Department of Ecology and Conservation Biology Texas A&M University 2258 TAMU College Station Texas77843USA
| | - David D. Briske
- Department of Ecology and Conservation Biology Texas A&M University 2258 TAMU College Station Texas77843USA
| | - Matthew C. Reeves
- U.S. Department of Agriculture, Forest Service Rocky Mountain Research Station 800 East Beckwith Avenue Missoula Montana59801USA
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25
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Throop HL, Archer SR, McClaran MP. Soil organic carbon in drylands: shrub encroachment and vegetation management effects dwarf those of livestock grazing. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2020; 30:e02150. [PMID: 32343858 DOI: 10.1002/eap.2150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 03/17/2020] [Accepted: 03/30/2020] [Indexed: 06/11/2023]
Abstract
Dryland ecosystems occur worldwide and play a prominent, but potentially shifting, role in global biogeochemical cycling. Widespread woody plant proliferation, often associated with declines in palatable grasses, has jeopardized livestock production in drylands and prompted attempts to reduce woody cover by chemical or mechanical means. Woody encroachment also has the potential to significantly alter terrestrial carbon storage. However, little is known of the long-term biogeochemical consequences of woody encroachment in the broader context of its interaction with common dryland land uses, including "brush management" (woody plant clearing) and livestock grazing. Present assessments exhibit considerable variation in the consequences of these land use/land cover changes, with evidence that brush management may counteract sizeable impacts of shrub encroachment on soil biogeochemical pools. A challenge to assessing the net effects of brush management in shrub-encroached grasslands on soil organic carbon (SOC) and total nitrogen (N) pools is that land management practices are typically considered in isolation, when they are co-occurring phenomena. Furthermore, few studies have assessed spatial patterns in brush management and how these are affected in decades following treatment on sites with contrasting grazing histories. To address these uncertainties and interactions, we quantified the impacts of shrub encroachment and their subsequent mortality resulting from brush management (herbicide application) on SOC and N pools in a Sonoran Desert grassland where long-term grazing manipulations (>100 yr) co-occur with shrub encroachment and brush management. Pools of SOC and N associated with herbicided shrubs declined markedly over ~40 yr, offsetting 66% of the increases from shrub encroachment. However, spatial patterns in SOC induced by shrubs persisted over the decades following brush management. Century-long protection from grazing did little to change SOC and N pools. Accordingly, shrub encroachment and shrub mortality from brush management each far outweighed livestock grazing impacts. Consideration of the patterns of SOC and N through space (e.g., bole-to-dripline gradients), time (e.g., shrub age/size), land use (e.g., livestock grazing and brush management), and their interactions will position us to improve predictions of SOC and N responses to land use/land cover change, inform C-based management decisions, and objectively evaluate trade-offs with other ecosystem services.
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Affiliation(s)
- Heather L Throop
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287, USA
- School of Life Sciences, Arizona State University, Tempe, Arizona, 85287, USA
| | - Steven R Archer
- School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, 85721-0043, USA
| | - Mitchel P McClaran
- School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, 85721-0043, USA
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26
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Monaco TA, Gunnell KL. Understory Vegetation Change Following Woodland Reduction Varies by Plant Community Type and Seeding Status: A Region-Wide Assessment of Ecological Benefits and Risks. PLANTS (BASEL, SWITZERLAND) 2020; 9:E1113. [PMID: 32872167 PMCID: PMC7570382 DOI: 10.3390/plants9091113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 08/19/2020] [Accepted: 08/27/2020] [Indexed: 12/03/2022]
Abstract
Woodland encroachment is a global issue linked to diminished ecosystem services, prompting the need for restoration efforts. However, restoration outcomes can be highly variable, making it difficult to interpret the ecological benefits and risks associated with woodland-reduction treatments within semiarid ecosystems. We addressed this uncertainty by assessing the magnitude and direction of vegetation change over a 15-year period at 129 sagebrush (Artemisia spp.) sites following pinyon (Pinus spp.) and juniper (Juniperus spp.) (P-J) reduction. Pretreatment vegetation indicated strong negative relationships between P-J cover and the abundance of understory plants (i.e., perennial grass and sagebrush cover) in most situations and all three components differed significantly among planned treatment types. Thus, to avoid confounding pretreatment vegetation and treatment type, we quantified overall treatment effects and tested whether distinct response patterns would be present among three dominant plant community types that vary in edaphic properties and occur within distinct temperature/precipitation regimes using meta-analysis (effect size = lnRR = ln[posttreatment cover/pretreatment cover]). We also quantified how restoration seedings contributed to overall changes in key understory vegetation components. Meta-analyses indicated that while P-J reduction caused significant positive overall effects on all shrub and herbaceous components (including invasive cheatgrass [Bromus tectorum] and exotic annual forbs), responses were contingent on treatment- and plant community-type combinations. Restoration seedings also had strong positive effects on understory vegetation by augmenting changes in perennial grass and perennial forb components, which similarly varied by plant community type. Collectively, our results identified specific situations where broad-scale efforts to reverse woodland encroachment substantially met short-term management goals of restoring valuable ecosystem services and where P-J reduction disposed certain plant community types to ecological risks, such as increasing the probability of native species displacement and stimulating an annual grass-fire cycle. Resource managers should carefully weigh these benefits and risks and incorporate additional, appropriate treatments and/or conservation measures for the unique preconditions of a given plant community in order to minimize exotic species responses and/or enhance desirable outcomes.
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Affiliation(s)
- Thomas A. Monaco
- U.S. Department of Agriculture, Agricultural Research Service, Forage and Range Research Laboratory, Utah State University, Logan, UT 84322-6300, USA
| | - Kevin L. Gunnell
- Great Basin Research Center, Utah Division of Wildlife Resources, Ephraim, UT 84627, USA;
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Stand-Level Transpiration Increases after Eastern Redcedar (Juniperus virginiana L.) Encroachment into the Midstory of Oak Forests. FORESTS 2020. [DOI: 10.3390/f11090901] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Eastern redcedar (Juniperus virginiana L., redcedar) encroachment is transitioning the oak-dominated Cross-Timbers of the southern Great Plain of the USA into mixed-species forests. However, it remains unknown how the re-assemblage of tree species in a semiarid to sub-humid climate affects species-specific water use and competition, and ultimately the ecosystem-level water budget. We selected three sites representative of oak, redcedar, and oak and redcedar mixed stands with a similar total basal area (BA) in a Cross-Timbers forest near Stillwater, Oklahoma. Sap flow sensors were installed in a subset of trees in each stand representing the distribution of diameter at breast height (DBH). Sap flow of each selected tree was continuously monitored over a period of 20 months, encompassing two growing seasons between May 2017 and December 2018. Results showed that the mean sap flow density (Sd) of redcedar was usually higher than post oaks (Quercus stellata Wangenh.). A structural equation model showed a significant correlation between Sd and shallow soil moisture for redcedar but not for post oak. At the stand level, the annual water use of the mixed species stand was greater than the redcedar or oak stand of similar total BA. The transition of oak-dominated Cross-Timbers to redcedar and oak mixed forest will increase stand-level transpiration, potentially reducing the water available for runoff or recharge to groundwater.
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28
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Driscoll AW, Bitter NQ, Sandquist DR, Ehleringer JR. Multidecadal records of intrinsic water-use efficiency in the desert shrub Encelia farinosa reveal strong responses to climate change. Proc Natl Acad Sci U S A 2020; 117:18161-18168. [PMID: 32719142 PMCID: PMC7414048 DOI: 10.1073/pnas.2008345117] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
While tree rings have enabled interannual examination of the influence of climate on trees, this is not possible for most shrubs. Here, we leverage a multidecadal record of annual foliar carbon isotope ratio collections coupled with 39 y of survey data from two populations of the drought-deciduous desert shrub Encelia farinosa to provide insight into water-use dynamics and climate. This carbon isotope record provides a unique opportunity to examine the response of desert shrubs to increasing temperature and water stress in a region where climate is changing rapidly. Population mean carbon isotope ratios fluctuated predictably in response to interannual variations in temperature, vapor pressure deficit, and precipitation, and responses were similar among individuals. We leveraged the well-established relationships between leaf carbon isotope ratios and the ratio of intracellular to ambient CO2 concentrations to calculate intrinsic water-use efficiency (iWUE) of the plants and to quantify plant responses to long-term environmental change. The population mean iWUE value increased by 53 to 58% over the study period, much more than the 20 to 30% increase that has been measured in forests [J. Peñuelas, J. G. Canadell, R. Ogaya, Glob. Ecol. Biogeogr. 20, 597-608 (2011)]. Changes were associated with both increased CO2 concentration and increased water stress. Individuals whose lifetimes spanned the entire study period exhibited increases in iWUE that were very similar to the population mean, suggesting that there was significant plasticity within individuals rather than selection at the population scale.
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Affiliation(s)
- Avery W Driscoll
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112
| | - Nicholas Q Bitter
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112
| | - Darren R Sandquist
- Department of Biological Science, California State University, Fullerton, CA 92834
| | - James R Ehleringer
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112;
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Winkler DE, Belnap J, Duniway MC, Hoover D, Reed SC, Yokum H, Gill R. Seasonal and individual event-responsiveness are key determinants of carbon exchange across plant functional types. Oecologia 2020; 193:811-825. [PMID: 32728948 DOI: 10.1007/s00442-020-04718-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Accepted: 07/20/2020] [Indexed: 11/29/2022]
Abstract
Differentiation in physiological activity is a critical component of resource partitioning in resource-limited environments. For example, it is crucial to understand how plant physiological performance varies through time for different functional groups to forecast how terrestrial ecosystems will respond to change. Here, we tracked the seasonal progress of 13 plant species representing C3 shrub, perennial C3 and C4 grass, and annual forb functional groups of the Colorado Plateau, USA. We tested for differences in carbon assimilation strategies and how photosynthetic rates related to recent, seasonal, and annual precipitation and temperature variables. Despite seasonal shifts in species presence and activity, we found small differences in seasonally weighted annual photosynthetic rates among groups. However, differences in the timing of maximum assimilation (Anet) were strongly functional group-dependent. C3 shrubs employed a relatively consistent, low carbon capture strategy and maintained activity year-round but switched to a rapid growth strategy in response to recent climate conditions. In contrast, grasses maintained higher carbon capture during spring months when all perennials had maximum photosynthetic rates, but grasses were dormant during months when shrubs remained active. Perennial grass Anet rates were explained in part by precipitation accumulated during the preceding year and average maximum temperatures during the past 48 h, a result opposite to shrubs. These results lend insight into diverse physiological strategies and their connections to climate, and also point to the potential for shrubs to increase in abundance in response to increased climatic variability in drylands, given shrubs' ability to respond rapidly to changing conditions.
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Affiliation(s)
- Daniel E Winkler
- U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, 84532, USA.
| | - Jayne Belnap
- U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, 84532, USA
| | - Michael C Duniway
- U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, 84532, USA
| | - David Hoover
- Rangeland Resources and Systems Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Fort Collins, 80526, USA
| | - Sasha C Reed
- U.S. Geological Survey, Southwest Biological Science Center, Moab, UT, 84532, USA
| | - Hannah Yokum
- Department of Biology, Brigham Young University, Provo, UT, 84604, USA
| | - Richard Gill
- Department of Biology, Brigham Young University, Provo, UT, 84604, USA
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Climate Change, Rangelands, and Sustainability of Ranching in the Western United States. SUSTAINABILITY 2020. [DOI: 10.3390/su12124942] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Accelerated climate change is a global challenge that is increasingly putting pressure on the sustainability of livestock production systems that heavily depend on rangeland ecosystems. Rangeland management practices have low potential to sequester greenhouse gases. However, mismanagement of rangelands and their conversion into ex-urban, urban, and industrial landscapes can significantly exacerbate the climate change process. Under conditions of more droughts, heat waves, and other extreme weather events, management of risks (climate, biological, financial, political) will probably be more important to the sustainability of ranching than capability to expand output of livestock products in response to rising demand due to population growth. Replacing traditional domestic livestock with a combination of highly adapted livestock and game animals valued for both hunting and meat may be the best strategy on many arid rangelands. Eventually, traditional ranching could become financially unsound across large areas if climate change is not adequately addressed. Rangeland policy, management, and research will need to be heavily focused on the climate change problem.
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31
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Houghton RA. Terrestrial fluxes of carbon in GCP carbon budgets. GLOBAL CHANGE BIOLOGY 2020; 26:3006-3014. [PMID: 32100912 DOI: 10.1111/gcb.15050] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 02/12/2020] [Indexed: 06/10/2023]
Abstract
The Global Carbon Project (GCP) has published global carbon budgets annually since 2007 (Canadell et al. [2007], Proc Natl Acad Sci USA, 104, 18866-18870; Raupach et al. [2007], Proc Natl Acad Sci USA, 104, 10288-10293). There are many scientists involved, but the terrestrial fluxes that appear in the budgets are not well understood by ecologists and biogeochemists outside of that community. The purpose of this paper is to make the terrestrial fluxes of carbon in those budgets more accessible to a broader community. The GCP budget is composed of annual perturbations from pre-industrial conditions, driven by addition of carbon to the system from combustion of fossil fuels and by transfers of carbon from land to the atmosphere as a result of land use. The budget includes a term for each of the major fluxes of carbon (fossil fuels, oceans, land) as well as the rate of carbon accumulation in the atmosphere. Land is represented by two terms: one resulting from direct anthropogenic effects (Land Use, Land-Use Change, and Forestry or land management) and one resulting from indirect anthropogenic (e.g., CO2 , climate change) and natural effects. Each of these two net terrestrial fluxes of carbon, in turn, is composed of opposing gross emissions and removals (e.g., deforestation and forest regrowth). Although the GCP budgets have focused on the two net terrestrial fluxes, they have paid little attention to the gross components, which are important for a number of reasons, including understanding the potential for land management to remove CO2 from the atmosphere and understanding the processes responsible for the sink for carbon on land. In contrast to the net fluxes of carbon, which are constrained by the global carbon budget, the gross fluxes are largely unconstrained, suggesting that there is more uncertainty than commonly believed about how terrestrial carbon emissions will respond to future fossil fuel emissions and a changing climate.
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Peters DPC, Okin GS, Herrick JE, Savoy HM, Anderson JP, Scroggs SLP, Zhang J. Modifying connectivity to promote state change reversal: the importance of geomorphic context and plant-soil feedbacks. Ecology 2020; 101:e03069. [PMID: 32297657 PMCID: PMC7569510 DOI: 10.1002/ecy.3069] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 02/10/2020] [Accepted: 03/16/2020] [Indexed: 11/06/2022]
Abstract
Alternative states maintained by feedbacks are notoriously difficult, if not impossible, to reverse. Although positive interactions that modify soil conditions may have the greatest potential to alter self-reinforcing feedbacks, the conditions leading to these state change reversals have not been resolved. In a 9-yr study, we modified horizontal connectivity of resources by wind or water on different geomorphic surfaces in an attempt to alter plant-soil feedbacks and shift woody-plant-dominated states back toward perennial grass dominance. Modifying connectivity resulted in an increase in litter cover regardless of the vector of transport (wind, water) followed by an increase in perennial grass cover 2 yr later. Modifying connectivity was most effective on sandy soils where wind is the dominant vector, and least effective on gravelly soils on stable surfaces with low sediment movement by water. We found that grass cover was related to precipitation in the first 5 yr of our study, and plant-soil feedbacks developed following 6 yr of modified connectivity to overwhelm effects of precipitation on sandy, wind-blown soils. These feedbacks persisted through time under variable annual rainfall. On alluvial soils, either plant-soil feedbacks developed after 7 yr that were not persistent (active soils) or did not develop (stable soils). This novel approach has application to drylands globally where desertified lands have suffered losses in ecosystem services, and to other ecosystems where connectivity-mediated feedbacks modified at fine scales can be expected to impact plant recovery and state change reversals at larger scales, in particular for wind-impacted sites.
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Affiliation(s)
- Debra P C Peters
- U.S. Department of Agriculture, Agricultural Research Service, Jornada Experimental Range Unit, Las Cruces, New Mexico, 88003, USA.,Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA
| | - Gregory S Okin
- Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA.,Department of Geography, University of California, Los Angeles, California, 90095, USA
| | - Jeffrey E Herrick
- U.S. Department of Agriculture, Agricultural Research Service, Jornada Experimental Range Unit, Las Cruces, New Mexico, 88003, USA.,Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA
| | - Heather M Savoy
- U.S. Department of Agriculture, Agricultural Research Service, Jornada Experimental Range Unit, Las Cruces, New Mexico, 88003, USA.,Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA
| | - John P Anderson
- Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA.,Jornada Experimental Range Department, New Mexico State University, Las Cruces, New Mexico, 88003, USA
| | - Stacey L P Scroggs
- Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA.,Department of Biology, New Mexico State University, Las Cruces, New Mexico, 88003, USA
| | - Junzhe Zhang
- Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, 88003, USA.,Department of Geography, University of California, Los Angeles, California, 90095, USA
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Sühs RB, Giehl ELH, Peroni N. Preventing traditional management can cause grassland loss within 30 years in southern Brazil. Sci Rep 2020; 10:783. [PMID: 31964935 PMCID: PMC6972928 DOI: 10.1038/s41598-020-57564-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 12/31/2019] [Indexed: 11/12/2022] Open
Abstract
Woody encroachment threatens several ecosystems around the world. In general, management of grasslands includes regulation of fire and grazing regimes. Changes in these two types of disturbances are potential drivers of woody encroachment. Here we assessed how the traditional management carried out by local landholders affects a highland grassland ecosystem in southern Brazil. We hypothesized that grasslands converted to protected areas undergo fast woody encroachment. To reconstruct changes in vegetation, we interviewed former and current landholders and coupled their knowledge with an analysis of aerial and satellite images. During the first 11 years without fire and cattle, woody encroachment in grasslands increased exponentially. Woody encroachment occurred mostly by the replacement of grasslands by shrublands. Meanwhile, grasslands under traditional management remained almost unchanged for the last 40 years. The management of fire by local landholders has been part of their traditional practices for decades. Such management prevents large-scale wildfires and maintains natural highland grasslands. The quick pace of shrub encroachment in such grasslands threatens its exclusive diversity, human well-being and regional cultural heritage. Thus, conservation policies are needed to regulate and instruct about the use of fire as a management tool in highland grasslands of southern Brazil.
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Affiliation(s)
- Rafael Barbizan Sühs
- Department of Ecology and Zoology, Federal University of Santa Catarina (UFSC), Florianopolis, Santa Catarina, Brazil.
| | - Eduardo Luís Hettwer Giehl
- Department of Ecology and Zoology, Federal University of Santa Catarina (UFSC), Florianopolis, Santa Catarina, Brazil
| | - Nivaldo Peroni
- Department of Ecology and Zoology, Federal University of Santa Catarina (UFSC), Florianopolis, Santa Catarina, Brazil
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O'Connor RC, Taylor JH, Nippert JB. Browsing and fire decreases dominance of a resprouting shrub in woody encroached grassland. Ecology 2019; 101:e02935. [PMID: 31746458 DOI: 10.1002/ecy.2935] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2019] [Revised: 09/20/2019] [Accepted: 10/18/2019] [Indexed: 11/12/2022]
Abstract
North American grasslands have experienced increased relative abundance of shrubs and trees over the last 150 yr. Alterations in herbivore composition, abundance, and grazing pressure along with changes in fire frequency are drivers that can regulate the transition from grassland to shrubland or woodland (a process known as woody encroachment). Historically, North American grasslands had a suite of large herbivores that grazed and/or browsed (i.e., bison, elk, pronghorn, deer), as well as frequent and intense fires. In the tallgrass prairie, many large native ungulates were extirpated by the 1860s, corresponding with increased homesteading (which led to decreased fire frequencies and intensities). Changes in the frequency and intensity of these two drivers (browsing and fire) have coincided with woody encroachment in tallgrass prairie. Within tallgrass prairie, woody encroachment can be categorized in to two groups: non-resprouting species that can be killed with fire and resprouting species that cannot be killed with fire. Resprouting species require additional active management strategies to decrease abundance and eventually be removed from the ecosystem. In this study, we investigated plant cover, ramet density, and physiological effects of continuous simulated browsing and prescribed fire on Cornus drummondii C.A. Mey, a resprouting clonal native shrub species. Browsing reduced C. drummondii canopy cover and increased grass cover. We also observed decreased ramet density, which allowed for more infilling of grasses. Photosynthetic rates between browsed and unbrowsed control shrubs did not increase in 2015 or 2016. In 2017, photosynthetic rates for browsed shrubs were higher in the unburned site than the unbrowsed control shrubs at the end of the growing season. Additionally, after the prescribed fire, browsed shrubs had ~90% decreased cover, ~50% reduced ramet density, and grass cover increased by ~80%. In the roots of browsed shrubs after the prescribed fire, nonstructural carbohydrates (NSC) experienced a twofold reduction in glucose and a threefold reduction in both sucrose and starch. The combined effects of browsing and fire show strong potential as a successful management tool to decrease the abundance of clonal-resprouting woody plants in mesic grasslands and illustrate the potential significance of browsers as a key driver in this ecosystem.
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Affiliation(s)
- Rory C O'Connor
- Division of Biology, Kansas State University, Manhattan, Kansas, 66506, USA.,O'Connor Rangeland Science, 970 South Lusk Street, Boise, Idaho, 83706, USA
| | - Jeffrey H Taylor
- Division of Biology, Kansas State University, Manhattan, Kansas, 66506, USA
| | - Jesse B Nippert
- Division of Biology, Kansas State University, Manhattan, Kansas, 66506, USA
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35
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Xu K, He L, Hu H, Wang Z, Lin M, Liu S, Du Y, Li Y, Wang G. Indirect effects of water availability in driving and predicting productivity in the Gobi desert. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 697:133952. [PMID: 31487587 DOI: 10.1016/j.scitotenv.2019.133952] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 08/15/2019] [Accepted: 08/15/2019] [Indexed: 06/10/2023]
Abstract
Climate is the fundamental determinant of plant metabolism and net primary productivity (NPP). However, whether climate drives NPP directly or indirectly is not well understand. The Gobi desert across a precipitation gradient in the arid zone provides an ideal naturally-controlled platform for studying the precipitation-productivity relationships. We conducted 3-year experiments in four Gobi desert shrublands across an aridity gradient in Gansu Province of China to test the relationship between water availability and shrub productivity as well as the relative importance of the possible factors driving productivity (using piecewise structural equation modeling) and to explore the appropriate variables for predicting productivity (using three spatial models). The results showed that water availability indirectly affected the NPP via stand biomass, while stand biomass had a significant direct effect on NPP regardless of whether the leaf water content and stand height were considered. The model based on stand size (71.6%) and the model that contained both stand size and water availability (72.3%) explained more of the variation in the water-NPP relationships than the model based on water availability (37.3%). Our findings suggest that even in extremely water-limited areas, the effects of water availability on plant growth and the kinetics of plant metabolism could be indirect via plant size, demonstrating the importance of plant size as an indicator of shrub productivity. This study explains the mechanisms underlying the NPP driving pattern and proposes a practical NPP model for arid ecosystems.
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Affiliation(s)
- Kang Xu
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Lingchao He
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Hanjian Hu
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Zhiwei Wang
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Maozi Lin
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Measurement and Control System for Coastal Basin Environment, Fujian Province University (Fuqing Branch of Fujian Normal University), Fuqing 350300, China
| | - Shun Liu
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Yuanyuan Du
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China
| | - Yan Li
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China; State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University, Hangzhou 311300, China
| | - Genxuan Wang
- College of Life Sciences, Zhejiang University, Hangzhou 310058, China.
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36
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A Three-Dimensional Assessment of Soil δ13C in a Subtropical Savanna: Implications for Vegetation Change and Soil Carbon Dynamics. SOIL SYSTEMS 2019. [DOI: 10.3390/soilsystems3040073] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tree/shrub encroachment into drylands is a geographically widespread vegetation change that often modifies soil organic carbon (SOC) storage and dynamics, and represents an important yet uncertain aspect of the global carbon (C) cycle. We quantified spatial patterns of soil δ13C to 1.2 m depth in a subtropical savanna to evaluate the magnitude and timing of woody encroachment, and its impacts on SOC dynamics. Woody encroachment dramatically altered soil δ13C spatial patterns throughout the profile; values were lowest in the interiors of woody patches, increased towards the peripheries of those patches, and reached highest values in the surrounding grasslands. Soil δ13C and 14C revealed this landscape was once dominated by C4 grasses. However, a rapid vegetation change occurred during the past 100–200 years, characterized by (1) the formation and expansion of woody patches across this landscape, and (2) increased C3 forb abundance within remnant grasslands. Tree/shrub encroachment has substantially increased SOC and the proportion of new SOC derived from C3 plants in the SOC pool. These findings support the emerging perspective that vegetation in many dryland ecosystems is undergoing dramatic and rapid increases in SOC storage, with implications for the C cycle at regional and global scales.
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37
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Espunyes J, Lurgi M, Büntgen U, Bartolomé J, Antonio Calleja J, Gálvez-Cerón A, Peñuelas J, Claramunt-López B, Serrano E. Different effects of alpine woody plant expansion on domestic and wild ungulates. GLOBAL CHANGE BIOLOGY 2019; 25:1808-1819. [PMID: 30737872 PMCID: PMC6522367 DOI: 10.1111/gcb.14587] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Accepted: 02/04/2019] [Indexed: 06/09/2023]
Abstract
Changes in land-use and climate affect the distribution and diversity of plant and animal species at different spatiotemporal scales. The extent to which species-specific phenotypic plasticity and biotic interactions mediate organismal adaptation to changing environments, however, remains poorly understood. Woody plant expansion is threatening the extent of alpine grasslands worldwide, and evaluating and predicting its effects on herbivores is of crucial importance. Here, we explore the impact of shrubification on the feeding efficiency of Pyrenean chamois (Rupicapra p. pyrenaica), as well as on the three most abundant coexisting domestic ungulate species: cattle, sheep and horses. We use observational diet composition from May to October and model different scenarios of vegetation availability where shrubland and woodland proliferate at the expense of grassland. We then predicted if the four ungulate species could efficiently utilize their food landscapes with their current dietary specificities measuring their niche breath in each scenario. We observed that the wild counterpart, due to a higher trophic plasticity, is less disturbed by shrubification compared to livestock, which rely primarily on herbaceous plants and will be affected 3.6 times more. Our results suggest that mixed feeders, such as chamois, could benefit from fallow landscapes, and that mountain farmers are at a growing economic risk worldwide due to changing land-use practices and climate conditions.
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Affiliation(s)
- Johan Espunyes
- Wildlife Ecology & Health Group (WE&H) and Servei d’Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona, Barcelona, Spain
| | - Miguel Lurgi
- Centre for Biodiversity Theory and Modelling. Theoretical and Experimental Ecology Station, CNRS-Paul Sabatier University, Moulis, France
| | - Ulf Büntgen
- Department of Geography, University of Cambridge, Cambridge, UK
- Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
- Global Change Research Centre (CzechGlobe), Brno, Czech Republic
- Department of Geography, Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Jordi Bartolomé
- Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Facultat de Veterinària, Universitat Autònoma de Barcelon, Barcelona, Spain
| | - Juan Antonio Calleja
- Unitat de botánica, Departament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, Bellaterra, Spain
- Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), Cerdanyola del Vallès, Spain
| | - Arturo Gálvez-Cerón
- Wildlife Ecology & Health Group (WE&H) and Servei d’Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona, Barcelona, Spain
- Facultad de ciencias pecuarias, Universidad de Nariño, Pasto, Colombia
| | - Josep Peñuelas
- Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), Cerdanyola del Vallès, Spain
- CSIC, Global Ecology Unit, CREAF-CSIC-Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Bernat Claramunt-López
- CREAF, Centre de Recerca Ecològica i Aplicacions Forestals, Edifici Ciències, Bellaterra Catalunya, Spain
- Unitat d’Ecologia, Departament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, Edifici Ciències, Bellaterra Catalunya, Spain
| | - Emmanuel Serrano
- Wildlife Ecology & Health Group (WE&H) and Servei d’Ecopatologia de Fauna Salvatge (SEFaS), Departament de Medicina i Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona, Barcelona, Spain
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Halpern CB, Antos JA, Kothari S, Olson AM. Past tree influence and prescribed fire exert strong controls on reassembly of mountain grasslands after tree removal. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2019; 29:e01860. [PMID: 30703273 DOI: 10.1002/eap.1860] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 01/03/2019] [Indexed: 06/09/2023]
Abstract
Woody-plant encroachment represents a global threat to grasslands. Although the causes and consequences of this regime shift have received substantial attention, the processes that constrain reassembly of the grassland state remain poorly understood. We experimentally tested two potentially important controls on reassembly, the past influence of trees and the effects of fire, in conifer-invaded grasslands (mountain meadows) of western Oregon. Previously, we had reconstructed the history of tree invasion at fine spatial and temporal resolution. Using small subplots (10 × 10 m) nested within larger (1-ha) experimental plots, we characterized the fine-scale mosaic of encroachment states, ranging from remnant meadow openings (minimally altered by trees) to century-old forests (lacking meadow species). Subsequently, we removed trees from six plots, of which three were broadcast burned and three remained unburned (except for localized burn piles). Within each plot, subplots were sampled before and periodically after tree removal to quantify the individual and interactive effects of past tree influence and fire on grassland community reassembly. Adjacent, uninvaded meadows served as reference sites. "Past tree influence" was defined as the multivariate (structural or compositional) distance of subplots to reference meadows prior to tree removal. "Reassembly" was defined as the distance, or change in distance, to reference meadows at final sampling. Consistent with theory, we observed greater reassembly of plant community structure than of composition, as loss of meadow specialists was offset by establishment of disturbance-adapted meadow generalists of similar growth form. Nevertheless, eight years after tree removal, most subplots remained structurally and compositionally distinct from reference meadows. Furthermore, fire had both destabilizing and inhibitory effects: it reduced survival of meadow specialists across the range of encroachment states and, where past tree influence was greater, it stalled reassembly by promoting expansion of a highly competitive native meadow sedge. The slow pace of reassembly, despite abundant open space, suggests strong seed limitation: a condition exacerbated by burning. We present a novel test of the importance of past tree influence and fire for restoration of tree-invaded grasslands, offering insights into how constraints on community reassembly vary along a continuum of tree-altered states.
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Affiliation(s)
- Charles B Halpern
- School of Environmental and Forest Sciences, University of Washington, Box 352100, Seattle, Washington, 98195-2100, USA
| | - Joseph A Antos
- Department of Biology, University of Victoria, P.O. Box 3020, Victoria, British Columbia, V8W 3N5, Canada
| | - Shan Kothari
- Department of Plant and Microbial Biology, University of Minnesota, 1479 Gortner Avenue, St. Paul, Minnesota, 55108, USA
| | - Annette M Olson
- Department of Integrative Biology, Oregon State University, Corvallis, Oregon, 97331, USA
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Shrub Encroachment Shapes Soil Nutrient Concentration, Stoichiometry and Carbon Storage in an Abandoned Subalpine Grassland. SUSTAINABILITY 2019. [DOI: 10.3390/su11061732] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Soil nutrient stoichiometry plays a substantial role in terrestrial carbon and nutrient cycling. However, the changes in soil nutrient stoichiometry with shrub encroachment (SE) remain poorly understood, especially in subalpine areas. We examined the changes in soil nutrient concentration, nutrient stoichiometry, and organic carbon (OC) storage (at a depth of 0–5, 5–10 and 10–20 cm) in three successional shrub encroachment stages (early, mid and late) in an abandoned subalpine Eulalia pallens (Hackel) Kuntze grassland. An ANOVA showed that SE did not produce serious soil acidification, but significantly increased the soil OC and total phosphorous (TP) concentration, and improved the stoichiometry ratio of soil OC to total nitrogen (OC:TN) in all layers. OC storage tended to increase with SE. SE thus did not indicate degradation of the grassland. A redundancy analysis (RDA) and partial RDA revealed that the shrub relative cover and soil water content were the most important factors affecting the soil nutrient concentration, that the soil available phosphorous (AP), nitrogen, potassium, calcium (ACa), and magnesium concentration and shrub relative cover were the most important factors influencing soil nutrient stoichiometry ratios, and that soil OC:TN, TN:TP, OC:TN:TP, and AP:ACa ratios, bulk density, and pH were the most important factors influencing soil OC storage over SE. Our study provides insights into SE in grassland areas, and potentially provides a useful reference for ongoing grassland conservation and restoration in subalpine regions.
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Daryanto S, Fu B, Zhao W. Evaluating the use of fire to control shrub encroachment in global drylands: A synthesis based on ecosystem service perspective. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 648:285-292. [PMID: 30118941 DOI: 10.1016/j.scitotenv.2018.08.140] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Revised: 08/06/2018] [Accepted: 08/10/2018] [Indexed: 06/08/2023]
Abstract
With the proliferation of woody plant species in much of the world's grasslands, human has manipulated landscape fire to return their forage provisioning service. Yet other ecosystem services (e.g., carbon sequestration, biodiversity conservation, erosion control) in the post-managed areas compared to those previously available in the shrub-encroached area are largely unknown, including trade-offs between ecosystem services. Using data from previous publications, we quantitatively synthesized the sustainability of fire as shrub management practice, expressed as its efficacy to control shrubs and its capacity to maintain different ecosystem services. A simple indicator (δ), defined as the ratio of an observed ecological attribute between area experiencing shrub management and untreated control, was used to quantify the changes. Our results showed that fire could be an effective strategy to control shrubs and to increase forage provisioning service (δherbaceous biomass = 1.39). However, there are possible trade-offs with other ecosystem services (e.g., erosion control, nutrient cycling) when a 54% increase in bare soil cover (δbare soil = 1.54) and ~74% loss of biological soil crusts cover (δbiological crust = 0.26) were found. Because increasing forage provisioning at the cost of other ecosystem services might not be sustainable, management should focus on strategies to minimize such trade-offs, which may include but not limited to rotational grazing, adjustment in stocking rate, or supplementary external inputs (e.g., fertilizer). Unless those measures are employed, there is possible emergence of a novel crash (i.e., vegetation- and resource-poor scabland) resulting from a combination of soil erosion and high vulnerability of burnt landscape to exotic species invasion.
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Affiliation(s)
- Stefani Daryanto
- State Key Laboratory of Earth Surface Processes and Resources Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China; Institute of Land Surface System and Sustainable Development, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China
| | - Bojie Fu
- State Key Laboratory of Earth Surface Processes and Resources Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China; Institute of Land Surface System and Sustainable Development, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China.
| | - Wenwu Zhao
- State Key Laboratory of Earth Surface Processes and Resources Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China; Institute of Land Surface System and Sustainable Development, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China
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Lecomte X, Caldeira MC, Catry FX, Fernandes PM, Jackson RB, Bugalho MN. Ungulates mediate trade‐offs between carbon storage and wildfire hazard in Mediterranean oak woodlands. J Appl Ecol 2018. [DOI: 10.1111/1365-2664.13310] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xavier Lecomte
- Forest Research CentreSchool of AgricultureUniversity of Lisbon Lisbon Portugal
| | - Maria C. Caldeira
- Forest Research CentreSchool of AgricultureUniversity of Lisbon Lisbon Portugal
| | - Filipe X. Catry
- Centre for Applied Ecology “Prof. Baeta Neves” (CEABN‐InBIO)School of AgricultureUniversity of Lisbon Lisbon Portugal
| | - Paulo M. Fernandes
- Centre for the Research and Technology of Agro‐Environmental and Biological Sciences (CITAB)University of Trás‐os‐Montes and Alto Douro (UTAD) Vila Real Portugal
| | - Robert B. Jackson
- Department of Earth System ScienceWoods Institute for the Environment, and Precourt Institute for EnergyStanford University Stanford California
| | - Miguel N. Bugalho
- Centre for Applied Ecology “Prof. Baeta Neves” (CEABN‐InBIO)School of AgricultureUniversity of Lisbon Lisbon Portugal
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Differing Responses to Rainfall Suggest More Than One Functional Type of Grassland in South Africa. REMOTE SENSING 2018. [DOI: 10.3390/rs10122055] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Grasslands, which represent around 40% of the terrestrial area, are mostly located in arid and semi-arid zones. Semiarid ecosystems in Africa have been identified as being particularly vulnerable to the impacts of increased human pressure on land, as well as enhanced climate variability. Grasslands are indeed very responsive to variations in precipitation. This study evaluates the sensitivity of the grassland ecosystem to precipitation variability in space and time, by identifying the factors controlling this response, based on monthly precipitation data from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) data from the Multi-angle Imaging SpectroRadiometer-High Resolution (MISR-HR) datasets, used as proxy for productivity, at 60 grassland sites in South Africa. Our results show that MISR-HR products adequately capture the spatial and temporal variability in productivity at scales that are relevant to this study, and they are therefore a good tool to study climate change impacts on ecosystem at small spatial scales over large spatial and temporal domains. We show that combining several determinants and accounting for legacies improves our ability to understand patterns, identify areas of vulnerability, and predict the future of grassland productivity. Mean annual precipitation is a good predictor of mean grassland productivity. The grasslands with a mean annual rainfall above about 530 mm have a different functional response to those receiving less than that amount of rain, on average. On the more arid and less fertile soils, large inter-annual variability reduces productivity. Our study suggests that grasslands on the more marginal soils are the most vulnerable to climate change.
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Impact of Eastern Redcedar Proliferation on Water Resources in the Great Plains USA—Current State of Knowledge. WATER 2018. [DOI: 10.3390/w10121768] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the Great Plains of the central United States, water resources for human and aquatic life rely primarily on surface runoff and local recharge from rangelands that are under rapid transformation to woodland by the encroachment of Eastern redcedar (redcedar; Juniperus virginiana) trees. In this synthesis, the current understanding and impact of redcedar encroachment on the water budget and water resources available for non-ecosystem use are reviewed. Existing studies concluded that the conversion from herbaceous-dominated rangeland to redcedar woodland increases precipitation loss to canopy interception and vegetation transpiration. The decrease of soil moisture, particularly for the subsurface soil layer, is widely documented. The depletion of soil moisture is directly related to the observed decrease in surface runoff, and the potential of deep recharge for redcedar encroached watersheds. Model simulations suggest that complete conversion of the rangelands to redcedar woodland at the watershed and basin scale in the South-central Great Plains would lead to reduced streamflow throughout the year, with the reductions of streamflow between 20 to 40% depending on the aridity of the climate of the watershed. Recommended topics for future studies include: (i) The spatial dynamics of redcedar proliferation and its impact on water budget across a regional hydrologic network; (ii) the temporal dynamics of precipitation interception by the herbaceous canopy; (iii) the impact of redcedar infilling into deciduous forests such as the Cross Timbers and its impact on water budget and water availability for non-ecosystem use; (iv) land surface and climate interaction and cross-scale hydrological modeling and forecasting; (v) impact of redcedar encroachment on sediment production and water quality; and (vi) assessment and efficacy of different redcedar control measures in restoring hydrological functions of watershed.
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Wang J, Xiao X, Zhang Y, Qin Y, Doughty RB, Wu X, Bajgain R, Du L. Enhanced gross primary production and evapotranspiration in juniper-encroached grasslands. GLOBAL CHANGE BIOLOGY 2018; 24:5655-5667. [PMID: 30215879 DOI: 10.1111/gcb.14441] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 06/15/2018] [Accepted: 08/22/2018] [Indexed: 06/08/2023]
Abstract
Woody plant encroachment (WPE) into grasslands has been occurring globally and may be accelerated by climate change in the future. This land cover change is expected to alter the carbon and water cycles, but it remains uncertain how and to what extent the carbon and water cycles may change with WPE into grasslands under current climate. In this study, we examined the difference of vegetation indices (VIs), evapotranspiration (ET), gross primary production (GPP), and solar-induced chlorophyll fluorescence (SIF) during 2000-2010 between grasslands and juniper-encroached grasslands. We also quantitatively assessed the changes of GPP and ET for grasslands with different proportions of juniper encroachment (JWPE). Our results suggested that JWPE increased the GPP, ET, greenness-related VIs, and SIF of grasslands. Mean annual GPP and ET were, respectively, ~55% and ~45% higher when grasslands were completely converted into juniper forests under contemporary climate during 2000-2010. The enhancement of annual GPP and ET for grasslands with JWPE varied over years ranging from about +20% GPP (~+30% for ET) in the wettest year (2007) to about twice as much GPP (~+55% for ET) in the severe drought year (2006) relative to grasslands without encroachment. Additionally, the differences in GPP and ET showed significant seasonal dynamics. During the peak growing season (May-August), GPP and ET for grasslands with JWPE were ~30% and ~40% higher on average. This analysis provided insights into how and to what degree carbon and water cycles were impacted by JWPE, which is vital to understanding how JWPE and ecological succession will affect the regional and global carbon and water budgets in the future.
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Affiliation(s)
- Jie Wang
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
| | - Xiangming Xiao
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
- Ministry of Education Key Laboratory of Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai, China
| | - Yao Zhang
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
- Department of Earth and Environment Engineering, Columbia University, New York, New York
| | - Yuanwei Qin
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
| | - Russell B Doughty
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
| | - Xiaocui Wu
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
| | - Rajen Bajgain
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
| | - Ling Du
- Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, Oklahoma
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Mureva A, Ward D, Pillay T, Chivenge P, Cramer M. Soil Organic Carbon Increases in Semi-Arid Regions while it Decreases in Humid Regions Due to Woody-Plant Encroachment of Grasslands in South Africa. Sci Rep 2018; 8:15506. [PMID: 30341313 PMCID: PMC6195563 DOI: 10.1038/s41598-018-33701-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 10/04/2018] [Indexed: 11/21/2022] Open
Abstract
Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachment. This change in land cover is thought to alter soil carbon (C) and nitrogen (N) storage in these ecosystems. Some studies have reported a negative correlation between soil C and N and mean annual precipitation while others have indicated that there is no relationship with mean annual precipitation. We quantified the changes in C and N pools and δ13C and δ15N values to a depth of 1 m in pairs of encroached and adjacent open grassland sites along a precipitation gradient from 300 mm to 1500 mm per annum in South Africa. Our study showed a negative correlation between changes in soil organic C stocks in the 0–100 cm soil layer and mean annual precipitation (MAP). The most humid site (1500 mm MAP) had less C in shrub-encroached sites while the drier sites (300–350 mm MAP) had more C than their paired open grasslands. This study generally showed soil organic C gains in low precipitation areas, with a threshold value between 750 mm and 900 mm. Our threshold value was higher than that found in North America, suggesting that one cannot extrapolate across continents.
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Affiliation(s)
- Admore Mureva
- School of Life Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, 3209, South Africa. .,Bindura University of Science Education, P. Bag 1020, Bindura, Zimbabwe.
| | - David Ward
- School of Life Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, 3209, South Africa.,Biological Sciences Department, Kent State University, Kent, 44242, USA
| | - Tiffany Pillay
- School of Life Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, 3209, South Africa
| | - Pauline Chivenge
- School of Life Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, 3209, South Africa.,International Crops Research Institute for the Semi-Arid Tropics, P. O. Box 776, Bulawayo, Zimbabwe
| | - Michael Cramer
- Department of Biological Sciences, University of Cape Town, Cape Town, 7700, South Africa
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Abstract
Woody plant encroachment has profound impacts on the sustainable management of water resources in water-limited ecosystems. However, our understanding of the effects of this global phenomenon on groundwater recharge at local and regional scales is limited. Here, we reviewed studies related to (i) recharge estimation methods; (ii) mechanisms by which woody plants impact groundwater recharge; (iii) impacts of woody plant on recharge across different soil and geology; (iv) hydrological repercussions of woody plant removal; and (v) research gaps and needs for groundwater studies. We identified six different methods: water balance, water table, isotopes, chloride mass balance, electrical geophysical imaging, and modeling were used to study the impact of woody encroachment on groundwater. Woody plant encroachment could alter soil infiltration rates, soil water storage, transpiration, interception, and subsurface pathways to affect groundwater recharge. The impact is highly variable, with the extent and the magnitude varying across the soil, substrate, plant cover, and topographic locations. Our review revealed mixed effects of woody plant removal on groundwater recharge. Studies of litter interception, root water uptake, soil moisture dynamics, and deep percolation along with the progression of woody plant encroachment are still limited, warranting further experimental studies focusing on groundwater recharge. Overall, information about woody plant encroachment impacts on groundwater resources across a range of scales is essential for long-range planning of water resources.
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Forty-Eight Years of Forest Succession: Tree Species Change across Four Forest Types in Mid-Missouri. FORESTS 2018. [DOI: 10.3390/f9100633] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the central and eastern United States, many forest ecosystems have undergone recent shifts in composition and structure that may conflict with contemporary management objectives. Long-term forest inventory data were used to determine patterns of forest succession over a 48-year period for four forest types in mid-Missouri: bottomlands, dry ridge and slope, glade-like, and mesic slopes. All forest types increased in stand basal area and overstory quadratic mean diameter through time, with concomitant decreases in the number of midstory trees. Sugar maple (Acer saccharum Marshall) increased in importance value on dry ridge and slope and mesic slope forest types, largely due to the accumulation of trees in smaller diameter classes. White oak (Quercus alba L.) increased in overstory basal area in dry ridge and slope plots through the duration of the study, whereas black oak (Quercus velutina Lam.) and Shumard oak (Quercus shumardii Buckley) decreased in overstory density and basal area through time. Oak stems were nearly absent from the midstory across forest types in the recent sampling, suggesting future challenges for maintaining oak-dominated canopies following attrition of canopy trees through time on upland forest types. In glade-like plots, eastern redcedar (Juniperus virginiana L.) increased in both overstory density and basal area through time, and Shumard oak decreased in density. The importance value of chinkapin oak (Quercus muehlenbergii Engelm.) in the overstory decreased through time in glade-like plots, largely due to the increase in density of eastern redcedar rather than the loss of chinkapin oak from the overstory. The patterns of succession in this forest landscape of mid-Missouri suggest that forest management may be needed to address two common contemporary concerns: (1) the need for increasing oak advance reproduction and recruitment to maintain oak as a canopy species; and (2) reducing eastern redcedar encroachment for glade restoration and management.
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Huang CY, Archer SR, McClaran MP, Marsh SE. Shrub encroachment into grasslands: end of an era? PeerJ 2018; 6:e5474. [PMID: 30202645 PMCID: PMC6129137 DOI: 10.7717/peerj.5474] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 07/15/2018] [Indexed: 11/20/2022] Open
Abstract
Shifts in the abundance of grasses and woody plants in drylands have occurred several times during the Holocene. However, our understanding of the rates and dynamics of this state-change in recent decades is limited to scattered studies conducted at disparate spatial and temporal scales; the potential misperceptions of shrub cover change could be remedied using cross spatiotemporal scale analyses that link field observations, repeat ground-level photography and remote sensing perspectives. The study was conducted across a semi-arid landscape in southern Arizona. Local data from long-term transects revealed three distinct chronological phases of shrub cover change: expansion (1961-1991, 0.7% y-1), decline (1992-1997, -2.3% y-1) and stabilization (1998-2012, 22-25% with no net cover change). Twenty-eight years (1984-2011) of broad-scale Landsat Thematic Mapper assessments confirm that shrub cover has been relatively stable in recent decades regardless of grazing regimes and landforms with the exception of the proliferation of succulents at lower elevations (verified by repeat photography acquired in 1987 and 2015) where the physical environment is the harshest, reflecting elevated temperature and winter precipitation deficit. Warmer, drier future climates are predicted to reduce woody plant carrying capacity and promote a shift to xerophytic succulents.
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Affiliation(s)
- Cho-Ying Huang
- Department of Geography, National Taiwan University, Taipei, Taiwan.,Research Center for Future Earth, National Taiwan University, Taipei, Taiwan
| | - Steven R Archer
- School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, United States of America
| | - Mitchel P McClaran
- School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, United States of America
| | - Stuart E Marsh
- School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, United States of America
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Wilcox BP, Birt A, Archer SR, Fuhlendorf SD, Kreuter UP, Sorice MG, van Leeuwen WJD, Zou CB. Viewing Woody-Plant Encroachment through a Social–Ecological Lens. Bioscience 2018. [DOI: 10.1093/biosci/biy051] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Bradford P Wilcox
- Department of Ecosystem Science and Management at Texas A&M University, in College Station
| | - Andrew Birt
- Department of Ecosystem Science and Management at Texas A&M University, in College Station
| | - Steven R Archer
- School of Natural Resources and the Environment at the University of Arizona, in Tucson
| | - Samuel D Fuhlendorf
- Department of Natural Resource Management at Oklahoma State University, in Stillwater
| | - Urs P Kreuter
- Department of Ecosystem Science and Management at Texas A&M University, in College Station
| | - Michael G Sorice
- Department of Forest Resources and Environmental Conservation at Virginia Tech, in Blacksburg
| | | | - Chris B Zou
- Department of Natural Resource Management at Oklahoma State University, in Stillwater
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