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Chen L, Li M, Li C, Zheng W, Liu R. Different Physiological Responses to Continuous Drought between Seedlings and Younger Individuals of Haloxylon ammodendron. PLANTS (BASEL, SWITZERLAND) 2023; 12:3683. [PMID: 37960040 PMCID: PMC10647405 DOI: 10.3390/plants12213683] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 10/18/2023] [Accepted: 10/18/2023] [Indexed: 11/15/2023]
Abstract
Drought is an important environmental factor that influences physiological processes in plants; however, few studies have examined the physiological mechanisms underlying plants' responses to continuous drought. In this study, the seedlings and younger individuals of Haloxylon ammodendron were experimentally planted in the southern part of the Gurbantunggut Desert. We measured their photosynthetic traits, functional traits and non-structural carbohydrate contents (NSCs) in order to assess the effects of continuous drought (at 15-day and 30-day drought points) on the plants' physiological responses. The results showed that at the 15-day (15 d) drought point, the leaf light-saturated net photosynthetic rate (An) values of both the seedlings and the younger individuals were decreased (by -68.9% and -45.2%, respectively). The intrinsic water use efficiency (iWUE) of the seedlings was significantly lower than that of the control group (-52.2%), but there was no diffenrence of iWUE observed in younger individuals. At the 30-day (30 d) drought point, a decrease in the An (-129.8%) of the seedlings was induced via biochemical inhibition, with a lower potential maximum photochemical rate (Fv/Fm, 0.42) compared with the control group, while a decrease in the An (-52.3%) of the younger individuals was induced due to lower stomatal conductance (gs, -50.5%). Our results indicated that prolonged drought induced a greater risk of seedling mortality as the relatively limited ability of stomatal regulation may increase the possibility of massive embolism, resulting in hydraulic failure.
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Affiliation(s)
- Lidan Chen
- State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; (L.C.); (M.L.)
- University of Chinese Academy of Sciences, Beijing 100049, China
- Fukang National Station of Observation and Research for Desert Ecosystem, Fukang 831505, China
| | - Minqing Li
- State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; (L.C.); (M.L.)
- University of Chinese Academy of Sciences, Beijing 100049, China
- Fukang National Station of Observation and Research for Desert Ecosystem, Fukang 831505, China
| | - Congjuan Li
- National Engineering Technology Research Center for Desert-Oasis Ecological Construction, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;
| | - Weihua Zheng
- Institute of Agricultural Quality Standards and Testing Technology, Xinjiang Academy of Agricultural Sciecnes, Urumuqi 830091, China;
| | - Ran Liu
- State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; (L.C.); (M.L.)
- University of Chinese Academy of Sciences, Beijing 100049, China
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2
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Fang S, He Z, Zhao M. Fifty years of change in the lower tree line in an arid coniferous forest in the Qilian Mountains, northwestern China. PLoS One 2023; 18:e0292682. [PMID: 37824484 PMCID: PMC10569624 DOI: 10.1371/journal.pone.0292682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Accepted: 09/26/2023] [Indexed: 10/14/2023] Open
Abstract
Tree line areas exhibited significant changes in response to climate change, including upward migration. Lower tree line dynamics are rarely studied, but as unique features in arid and semi-arid areas, they may influence forest distribution. Here, eight lower tree line plots in a Picea crassifolia Kom. (Qinghai spruce) forest in the arid and semi-arid Qilian Mountains of northwestern China were used to determine changes in tree line location and relationships with meteorological factors during 1968-2018. The results showed that the lower tree line descended by an average of 9.82 m during 1968 to 2018, and exhibited almost no change after 2008. The change in the lower tree line was significantly correlated with the annual average temperature (°C) and annual precipitation (mm) and may be affected by human activities. In the past 50 years, the lower tree line in arid areas exhibited a downward trend. Our findings indicate that the movement of the lower tree line is also an important aspect of climatic changes in coniferous forest distribution in arid and semi-arid mountains.
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Affiliation(s)
- Shu Fang
- College of Urban, Rural Planning and Architectural Engineering, Shangluo University, Shangluo, Shanxi, China
| | - Zhibin He
- Linze Inland River Basin Research Station, Chinese Ecosystem Research Network, Key Laboratory of Eco-hydrology of Inland River Basin, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu, China
| | - Minmin Zhao
- Key Laboratory of Hydrogeology, Center for Hydrogeology and Environmental Geology Survey, China Geological Survey, Baoding, Hebei, China
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3
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Barton AM, Poulos HM, Koch GW, Kolb TE, Thode AE. Detecting patterns of post-fire pine regeneration in a Madrean Sky Island with field surveys and remote sensing. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 867:161517. [PMID: 36638974 DOI: 10.1016/j.scitotenv.2023.161517] [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: 09/14/2022] [Revised: 01/05/2023] [Accepted: 01/06/2023] [Indexed: 06/17/2023]
Abstract
The American Southwest is experiencing drastic increases in aridity and wildfire incidence, triggering conversion of some frequent surface forests to non-forest. Extensive research has focused on these dynamics in regional ponderosa pine forests, but we know much less about Madrean pine-oak forests, which are broadly distributed from the Sierra Madre in Mexico to the Sky Island mountain ranges in the U.S. Increased fire incidence and drought in these forests are limiting pine regeneration and driving conversion of biodiverse forests to oak shrublands. We investigated regeneration patterns in Pinus engelmannii and P. leiophylla during severe drought 10 years after the Horseshoe Two Megafire in the Chiricahua Mountains, Arizona-a follow-up to an assessment five years post-fire. In long-term plots, we examined changes in pine seedling and resprout recruitment. Past research demonstrated that topography and fire severity influenced pine recruitment across environmental gradients. We investigated here whether Landsat-8 normalized difference vegetation index (NDVI) and evapotranspiration estimated by the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) added explanatory value to our understanding of these patterns. Conversion of Madrean pine-oak forest to oak shrublands continued 6-10 years post-fire. A dense, low oak canopy continued to coalesce in sites subject to severe fire. The importance of resprouts in P. leiophylla regeneration accelerated because these plants outgrew competing oak resprouts. Topography and fire severity (dNBR) were important predictors of 2021 patterns of pine recruitment. NDVI added explanatory value to these models, suggesting its potential in tracking forest dynamics. Evapotranspiration did not add value, likely because ECOSTRESS' larger pixel sizes and moving pixel locations created excessive subpixel heterogeneity in this highly dissected landscape. These models suggest that P. engelmannii is more drought sensitive, was more negatively affected by drought and fire, and is more at risk to shifts in climate and wildfires than P. leiophylla.
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Affiliation(s)
- Andrew M Barton
- Department of Biology, University of Maine at Farmington, Farmington, ME 04938, USA.
| | - Helen M Poulos
- Wesleyan University, College of the Environment and Earth and Environmental Sciences, Middletown, CT 06459, USA.
| | - George W Koch
- Department of Biological Sciences and the Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ 86011, USA.
| | - Thomas E Kolb
- School of Forestry, Northern Arizona University, Flagstaff, AZ 86011, USA.
| | - Andrea E Thode
- School of Forestry, Northern Arizona University, Flagstaff, AZ 86011, USA.
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4
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Zlobin IE, Kartashov AV, Ivanov YV, Ivanova AI, Kuznetsov VV. Stem notching decreases stem hydraulic conductance but does not influence drought impacts and post-drought recovery in Scots pine and Norway spruce. PHYSIOLOGIA PLANTARUM 2022; 174:e13813. [PMID: 36326172 DOI: 10.1111/ppl.13813] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 10/24/2022] [Accepted: 10/26/2022] [Indexed: 06/16/2023]
Abstract
The tight connection between the deterioration of xylem function and plant mortality under drought is well recognized. However, a lack of mechanistic understanding of how substantial conductivity loss influences plant performance under drought and during post-drought recovery hinders our ability to model tree responses to drought stress. We artificially induced a loss of 50% of xylem conducting area in Scots pine and Norway spruce saplings by stem notching and investigated plant performance under drought and during post-drought recovery. Plant mortality, xylem hydraulic conductivity, leaf water status and stomatal conductance were measured. We observed no preferential mortality of top plant parts (above the notches) compared to basal plant parts (below the notches), and no consistent trend in hydraulic conductivity loss was observed between top and basal parts of dying plants. Stem hydraulic conductivity, water status of the needles and stomatal conductance changed similarly between the top and basal parts during drought and post-drought recovery, which indicated the substantial hydraulic overcapacity of the stems. The recovery of stomatal conductance demonstrated prominent hysteresis due to non-hydraulic stomatal limitations. The results obtained are highly important for modelling the influence of plant hydraulic impairment on plant performance under drought and during post-drought recovery.
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Affiliation(s)
- Ilya E Zlobin
- K.A. Timiryazev Institute of Plant Physiology RAS, Moscow, Russia
| | | | - Yury V Ivanov
- K.A. Timiryazev Institute of Plant Physiology RAS, Moscow, Russia
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5
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The aboveground and belowground growth characteristics of juvenile conifers in the southwestern United States. Ecosphere 2021. [DOI: 10.1002/ecs2.3839] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
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6
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Sapes G, Sala A. Relative water content consistently predicts drought mortality risk in seedling populations with different morphology, physiology and times to death. PLANT, CELL & ENVIRONMENT 2021; 44:3322-3335. [PMID: 34251033 DOI: 10.1111/pce.14149] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 07/08/2021] [Indexed: 05/14/2023]
Abstract
Predicted increases in forest drought mortality highlight the need for predictors of incipient drought-induced mortality (DIM) risk that enable proactive large-scale management. Such predictors should be consistent across plants with varying morphology and physiology. Because of their integrative nature, indicators of water status are promising candidates for real-time monitoring of DIM, particularly if they standardize morphological differences among plants. We assessed the extent to which differences in morphology and physiology between Pinus ponderosa populations influence time to mortality and the predictive power of key indicators of DIM risk. Time to incipient mortality differed between populations but occurred at the same relative water content (RWC) and water potential (WP). RWC and WP were accurate predictors of drought mortality risk. These results highlight that variables related to water status capture critical thresholds during DIM and the associated dehydration processes. Both WP and RWC are promising candidates for large-scale assessments of DIM risk. RWC is of special interest because it allows comparisons across different morphologies and can be remotely sensed. Our results offer promise for real-time landscape-level monitoring of DIM and its global impacts in the near term.
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Affiliation(s)
- Gerard Sapes
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
- Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, Minnesota, USA
| | - Anna Sala
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
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7
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McGregor IR, Helcoski R, Kunert N, Tepley AJ, Gonzalez-Akre EB, Herrmann V, Zailaa J, Stovall AEL, Bourg NA, McShea WJ, Pederson N, Sack L, Anderson-Teixeira KJ. Tree height and leaf drought tolerance traits shape growth responses across droughts in a temperate broadleaf forest. THE NEW PHYTOLOGIST 2021; 231:601-616. [PMID: 33049084 DOI: 10.1111/nph.16996] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 10/02/2020] [Indexed: 06/11/2023]
Abstract
As climate change drives increased drought in many forested regions, mechanistic understanding of the factors conferring drought tolerance in trees is increasingly important. The dendrochronological record provides a window through which we can understand how tree size and traits shape growth responses to droughts. We analyzed tree-ring records for 12 species in a broadleaf deciduous forest in Virginia (USA) to test hypotheses for how tree height, microenvironment characteristics, and species' traits shaped drought responses across the three strongest regional droughts over a 60-yr period. Drought tolerance (resistance, recovery, and resilience) decreased with tree height, which was strongly correlated with exposure to higher solar radiation and evaporative demand. The potentially greater rooting volume of larger trees did not confer a resistance advantage, but marginally increased recovery and resilience, in sites with low topographic wetness index. Drought tolerance was greater among species whose leaves lost turgor (wilted) at more negative water potentials and experienced less shrinkage upon desiccation. The tree-ring record reveals that tree height and leaf drought tolerance traits influenced growth responses during and after significant droughts in the meteorological record. As climate change-induced droughts intensify, tall trees with drought-sensitive leaves will be most vulnerable to immediate and longer-term growth reductions.
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Affiliation(s)
- Ian R McGregor
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Center for Geospatial Analytics, North Carolina State University, Raleigh, NC, 27607, USA
| | - Ryan Helcoski
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
| | - Norbert Kunert
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Center for Tropical Forest Science-Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Panama, Republic of Panama
| | - Alan J Tepley
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Canadian Forest Service, Northern Forestry Centre, Edmonton, AB, T6H 3S5, Canada
| | - Erika B Gonzalez-Akre
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
| | - Valentine Herrmann
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
| | - Joseph Zailaa
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Biological Sciences Department, California State University, Los Angeles, CA, 90032, USA
| | - Atticus E L Stovall
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Department of Environmental Sciences, University of Virginia, Charlottesville, VA, 22903, USA
- NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
| | - Norman A Bourg
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
| | - William J McShea
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
| | | | - Lawren Sack
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
- Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Kristina J Anderson-Teixeira
- Conservation Ecology Center, Smithsonian Conservation Biology Institute, National Zoological Park, Front Royal, VA, 22630, USA
- Center for Tropical Forest Science-Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Panama, Republic of Panama
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8
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Venturas MD, Todd HN, Trugman AT, Anderegg WRL. Understanding and predicting forest mortality in the western United States using long-term forest inventory data and modeled hydraulic damage. THE NEW PHYTOLOGIST 2021; 230:1896-1910. [PMID: 33112415 DOI: 10.1111/nph.17043] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 10/20/2020] [Indexed: 06/11/2023]
Abstract
Global warming is expected to exacerbate the duration and intensity of droughts in the western United States, which may lead to increased tree mortality. A prevailing proximal mechanism of drought-induced tree mortality is hydraulic damage, but predicting tree mortality from hydraulic theory and climate data still remains a major scientific challenge. We used forest inventory data and a plant hydraulic model (HM) to address three questions: can we capture regional patterns of drought-induced tree mortality with HM-predicted damage thresholds; do HM metrics improve predictions of mortality across broad spatial areas; and what are the dominant controls of forest mortality when considering stand characteristics, climate metrics, and simulated hydraulic stress? We found that the amount of variance explained by models predicting mortality was limited (R2 median = 0.10, R2 range: 0.00-0.52). HM outputs, including hydraulic damage and carbon assimilation diagnostics, moderately improve mortality prediction across the western US compared with models using stand and climate predictors alone. Among factors considered, metrics of stand density and tree size tended to be some of the most critical factors explaining mortality, probably highlighting the important roles of structural overshoot, stand development, and biotic agent host selection and outbreaks in mortality patterns.
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Affiliation(s)
- Martin D Venturas
- School of Biological Sciences, University of Utah, Salt Lake City, UT, 84112, USA
| | - Henry N Todd
- School of Biological Sciences, University of Utah, Salt Lake City, UT, 84112, USA
| | - Anna T Trugman
- Department of Geography, University of California Santa Barbara, Santa Barbara, CA, 93106, USA
| | - William R L Anderegg
- School of Biological Sciences, University of Utah, Salt Lake City, UT, 84112, USA
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9
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Sapes G, Demaree P, Lekberg Y, Sala A. Plant carbohydrate depletion impairs water relations and spreads via ectomycorrhizal networks. THE NEW PHYTOLOGIST 2021; 229:3172-3183. [PMID: 33280134 DOI: 10.1111/nph.17134] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 11/24/2020] [Indexed: 06/12/2023]
Abstract
Under prolonged drought and reduced photosynthesis, plants consume stored nonstructural carbohydrates (NSCs). Stored NSC depletion may impair the regulation of plant water balance, but the underlying mechanisms are poorly understood, and whether such mechanisms are independent of plant water deficit is not known. If so, carbon costs of fungal symbionts could indirectly influence plant drought tolerance through stored NSC depletion. We connected well-watered Pinus ponderosa seedling pairs via ectomycorrhizal (EM) networks where one seedling was shaded (D) and the other kept illuminated (LD) and compared responses to seedling pairs in full light (L). We measured plant NSCs, osmotic and water potential, and transfer of 13 CO2 through EM to explore mechanisms linking stored NSCs to plant water balance regulation and identify potential tradeoffs between plant water retention and EM fungi under carbon-limiting conditions. NSCs decreased from L to LD to D seedlings. Even without drought, NSC depletion impaired osmoregulation and turgor maintenance, both of which are critical for drought tolerance. Importantly, EM networks propagated NSC depletion and its negative effects on water retention from carbon stressed to nonstressed hosts. We demonstrate that NSC storage depletion influences turgor maintenance independently of plant water deficit and reveal carbon allocation tradeoffs between supporting fungal symbionts and retaining water.
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Affiliation(s)
- Gerard Sapes
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA
- Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Patrick Demaree
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA
| | - Ylva Lekberg
- MPG Ranch, Missoula, MT, 59801, USA
- W.A. Franke College of Forestry & Conservation, University of Montana, Missoula, MT, 59812, USA
| | - Anna Sala
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA
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10
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A climatic dipole drives short- and long-term patterns of postfire forest recovery in the western United States. Proc Natl Acad Sci U S A 2020; 117:29730-29737. [PMID: 33168732 DOI: 10.1073/pnas.2007434117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Researchers are increasingly examining patterns and drivers of postfire forest recovery amid growing concern that climate change and intensifying fires will trigger ecosystem transformations. Diminished seed availability and postfire drought have emerged as key constraints on conifer recruitment. However, the spatial and temporal extent to which recurring modes of climatic variability shape patterns of postfire recovery remain largely unexplored. Here, we identify a north-south dipole in annual climatic moisture deficit anomalies across the Interior West of the US and characterize its influence on forest recovery from fire. We use annually resolved establishment models from dendrochronological records to correlate this climatic dipole with short-term postfire juvenile recruitment. We also examine longer-term recovery trajectories using Forest Inventory and Analysis data from 989 burned plots. We show that annual postfire ponderosa pine recruitment probabilities in the northern Rocky Mountains (NR) and the southwestern US (SW) track the strength of the dipole, while declining overall due to increasing aridity. This indicates that divergent recovery trajectories may be triggered concurrently across large spatial scales: favorable conditions in the SW can correspond to drought in the NR that inhibits ponderosa pine establishment, and vice versa. The imprint of this climatic dipole is manifest for years postfire, as evidenced by dampened long-term likelihoods of juvenile ponderosa pine presence in areas that experienced postfire drought. These findings underscore the importance of climatic variability at multiple spatiotemporal scales in driving cross-regional patterns of forest recovery and have implications for understanding ecosystem transformations and species range dynamics under global change.
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11
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Topographic, soil, and climate drivers of drought sensitivity in forests and shrublands of the Pacific Northwest, USA. Sci Rep 2020; 10:18486. [PMID: 33116196 PMCID: PMC7595234 DOI: 10.1038/s41598-020-75273-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 10/13/2020] [Indexed: 11/30/2022] Open
Abstract
Climate change is anticipated to increase the frequency and intensity of droughts, with major impacts to ecosystems globally. Broad-scale assessments of vegetation responses to drought are needed to anticipate, manage, and potentially mitigate climate-change effects on ecosystems. We quantified the drought sensitivity of vegetation in the Pacific Northwest, USA, as the percent reduction in vegetation greenness under droughts relative to baseline moisture conditions. At a regional scale, shrub-steppe ecosystems—with drier climates and lower biomass—showed greater drought sensitivity than conifer forests. However, variability in drought sensitivity was considerable within biomes and within ecosystems and was mediated by landscape topography, climate, and soil characteristics. Drought sensitivity was generally greater in areas with higher elevation, drier climate, and greater soil bulk density. Ecosystems with high drought sensitivity included dry forests along ecotones to shrublands, Rocky Mountain subalpine forests, and cold upland sagebrush communities. In forests, valley bottoms and areas with low soil bulk density and high soil available water capacity showed reduced drought sensitivity, suggesting their potential as drought refugia. These regional-scale drought-sensitivity patterns discerned from remote sensing can complement plot-scale studies of plant physiological responses to drought to help inform climate-adaptation planning as drought conditions intensify.
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12
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Urza AK, Weisberg PJ, Dilts T. Evidence of widespread topoclimatic limitation for lower treelines of the Intermountain West, United States. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2020; 30:e02158. [PMID: 32365241 DOI: 10.1002/eap.2158] [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: 12/04/2019] [Revised: 03/24/2020] [Accepted: 04/03/2020] [Indexed: 06/11/2023]
Abstract
Many forests in dry mountain regions are characterized by a lower elevational treeline. Understanding the controls on the position of lower treeline is important for predicting future forest distributional shifts in response to global environmental change. Lower treelines currently at their climate limit are expected to be more sensitive to changing climate, whereas lower treelines constrained by non-climatic factors are less likely to respond directly to climate change but may be sensitive to other global change agents. In this study, we used existing vegetation classifications to map lower treelines for our 1.7 million km2 study region in the U. S. Intermountain West. We modeled topoclimatic drivers of lower treeline position for each of three dominant forest types to identify topoclimatically limited treelines. We then used spatial data of edaphic properties, recent fire, and land use to identify lower treelines potentially constrained above their ecophysiological limits by non-climatic processes. We found that the lower treeline ecotone of pinyon-juniper woodlands is largely limited by topoclimate and is likely to be sensitive to increasing temperatures and associated droughts, though these effects may be heterogeneously distributed across the landscape. In contrast, dry mixed-conifer lower treelines in the northern portion of the study area rarely reached their modeled topoclimatic limit, suggesting that non-climatic processes, including fire and land use, constrain the lower treeline above its ecophysiological limits in this forest type. Our results suggest that much of the lower treeline in the Intermountain West is currently climate limited and will thus be sensitive to ongoing climate changes. Lower treelines in other arid or semi-arid mountainous regions around the globe may also be strongly sensitive to climate, though treeline response to climate change will be mediated at the local scale by soil properties, biotic interactions, and natural or anthropogenic disturbances. Our regional study of lower treeline provides a framework for identifying the drivers of lower treeline formation and allows for more robust projections of future treeline dynamics, which are needed to anticipate shifting global distributions of the forest biome.
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Affiliation(s)
- Alexandra K Urza
- USDA Forest Service, Rocky Mountain Research Station, 920 Valley Road, Reno, Nevada, 89512, USA
- Program in Ecology, Evolution and Conservation Biology, University of Nevada-Reno, 1664 North Virginia Street, Reno, Nevada, 89557, USA
| | - Peter J Weisberg
- Program in Ecology, Evolution and Conservation Biology, University of Nevada-Reno, 1664 North Virginia Street, Reno, Nevada, 89557, USA
- Department of Natural Resources and Environmental Science, University of Nevada-Reno, 1664 North Virginia Street, Reno, Nevada, 89557, USA
| | - Thomas Dilts
- Department of Natural Resources and Environmental Science, University of Nevada-Reno, 1664 North Virginia Street, Reno, Nevada, 89557, USA
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13
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Harris LB, Taylor AH. Rain‐shadow forest margins resilient to low‐severity fire and climate change but not high‐severity fire. Ecosphere 2020. [DOI: 10.1002/ecs2.3258] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- Lucas B. Harris
- Department of Geography The Pennsylvania State University 302 Walker Building University Park Pennsylvania16802USA
| | - Alan H. Taylor
- Department of Geography Earth and Environmental Systems Institute The Pennsylvania State University 302 Walker Building University Park Pennsylvania16802USA
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14
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Miller ML, Roddy AB, Brodersen CR, McElrone AJ, Johnson DM. Anatomical and hydraulic responses to desiccation in emergent conifer seedlings. AMERICAN JOURNAL OF BOTANY 2020; 107:1177-1188. [PMID: 32754914 DOI: 10.1002/ajb2.1517] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Accepted: 04/23/2020] [Indexed: 06/11/2023]
Abstract
PREMISE The young seedling life stage is critical for reforestation after disturbance and for species migration under climate change, yet little is known regarding their basic hydraulic function or vulnerability to drought. Here, we sought to characterize responses to desiccation including hydraulic vulnerability, xylem anatomical traits, and impacts on other stem tissues that contribute to hydraulic functioning. METHODS Larix occidentalis, Pseudotsuga menziesii, and Pinus ponderosa (all ≤6 weeks old) were imaged using x-ray computed microtomography during desiccation to assess seedling biomechanical responses with concurrently measured hydraulic conductivity (ks ) and water potential (Ψ) to assess vulnerability to xylem embolism formation and other tissue damage. RESULTS In non-stressed samples for all species, pith and cortical cells appeared circular and well hydrated, but they started to empty and deform with decreasing Ψ which resulted in cell tearing and eventual collapse. Despite the severity of this structural damage, the vascular cambium remained well hydrated even under the most severe drought. There were significant differences among species in vulnerability to xylem embolism formation, with 78% xylem embolism in L. occidentalis by Ψ of -2.1 MPa, but only 47.7% and 62.1% in P. ponderosa and P. menziesii at -4.27 and -6.73 MPa, respectively. CONCLUSIONS Larix occidentalis seedlings appeared to be more susceptible to secondary xylem embolism compared to the other two species, but all three maintained hydration of the vascular cambium under severe stress, which could facilitate hydraulic recovery by regrowth of xylem when stress is relieved.
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Affiliation(s)
- Megan L Miller
- Department of Forest, Rangeland, and Fire Sciences, University of Idaho, 875 Perimeter Drive MS 1133, Moscow, ID, 83844, USA
| | - Adam B Roddy
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- School of Forestry & Environmental Studies, Yale University, New Haven, CT, 06511, USA
| | - Craig R Brodersen
- School of Forestry & Environmental Studies, Yale University, New Haven, CT, 06511, USA
| | - Andrew J McElrone
- Department of Viticulture and Enology, University of California, Davis, CA, 95616, USA
- USDA-ARS, Davis, CA, 95616, USA
| | - Daniel M Johnson
- Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, 30602, USA
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Coop JD, Parks SA, Stevens-Rumann CS, Crausbay SD, Higuera PE, Hurteau MD, Tepley A, Whitman E, Assal T, Collins BM, Davis KT, Dobrowski S, Falk DA, Fornwalt PJ, Fulé PZ, Harvey BJ, Kane VR, Littlefield CE, Margolis EQ, North M, Parisien MA, Prichard S, Rodman KC. Wildfire-Driven Forest Conversion in Western North American Landscapes. Bioscience 2020; 70:659-673. [PMID: 32821066 PMCID: PMC7429175 DOI: 10.1093/biosci/biaa061] [Citation(s) in RCA: 104] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest type or nonforest vegetation. Conversion implies major, extensive, and enduring changes in dominant species, life forms, or functions, with impacts on ecosystem services. In the present article, we synthesize a growing body of evidence of fire-driven conversion and our understanding of its causes across western North America. We assess our capacity to predict conversion and highlight important uncertainties. Increasing forest vulnerability to changing fire activity and climate compels shifts in management approaches, and we propose key themes for applied research coproduced by scientists and managers to support decision-making in an era when the prefire forest may not return.
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Affiliation(s)
- Jonathan D Coop
- School of Environment and Sustainability, Western Colorado University, Gunnison
| | - Sean A Parks
- Research ecologist with the Aldo Leopold Wilderness Research Institute, Rocky Mountain Research Station, US Forest Service, Missoula, Montana
| | | | - Shelley D Crausbay
- Senior scientist with Conservation Science Partners, Fort Collins, Colorado
| | - Philip E Higuera
- Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, Montana
| | | | - Alan Tepley
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Ellen Whitman
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Timothy Assal
- Department of Geography, Kent State University, Kent, Ohio
| | - Brandon M Collins
- Fire Research and Outreach, University of California, Berkeley, Berkeley, California, and with the Pacific Southwest Research Station, US Forest Service, in Davis, California
| | - Kimberley T Davis
- Department of Ecosystem and Conservation Sciences, University of Montana, Missoula
| | | | - Donald A Falk
- Natural Resources and the Environment, University of Arizona, Tucson
| | - Paula J Fornwalt
- Rocky Mountain Research Station, US Forest Service, Fort Collins, Colorado
| | - Peter Z Fulé
- School of Forestry, Northern Arizona University, Flagstaff
| | - Brian J Harvey
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Van R Kane
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Caitlin E Littlefield
- Caitlin Littlefield is a postdoctoral research associate, Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington
| | - Ellis Q Margolis
- US Geological Survey, New Mexico Landscapes Field Station, Santa Fe
| | - Malcolm North
- US Forest Service, Pacific Southwest Research Station, Mammoth Lakes, California
| | - Marc-André Parisien
- Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Canada
| | - Susan Prichard
- School of Environmental and Forest Sciences, University of Washington, Seattle
| | - Kyle C Rodman
- Department of Forest and Wildlife Ecology, University of Wisconsin, Madison
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16
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Ulrich DEM, Sevanto S, Peterson S, Ryan M, Dunbar J. Effects of Soil Microbes on Functional Traits of Loblolly Pine ( Pinus taeda) Seedling Families From Contrasting Climates. FRONTIERS IN PLANT SCIENCE 2020; 10:1643. [PMID: 31998333 PMCID: PMC6962191 DOI: 10.3389/fpls.2019.01643] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 11/21/2019] [Indexed: 05/31/2023]
Abstract
Examining factors that influence seedling establishment is essential for predicting the impacts of climate change on tree species' distributions. Seedlings originating from contrasting climates differentially express functional traits related to water and nutrient uptake and drought resistance that reflect their climate of origin and influence their responses to drought. Soil microbes may improve seedling establishment because they can enhance water and nutrient uptake and drought resistance. However, the relative influence of soil microbes on the expression of these functional traits between seedling families or populations from contrasting climates is unknown. To determine if soil microbes may differentially alter functional traits to enhance water and nutrient uptake and drought resistance between dry and wet families, seeds of loblolly pine families from the driest and wettest ends of its geographic range (dry, wet) were planted in sterilized sand (controls) or in sterilized sand inoculated with a soil microbial community (inoculated). Functional traits related to seedling establishment (germination), water and nutrient uptake and C allocation (root:shoot biomass ratio, root exudate concentration, leaf C:N, leaf N isotope composition (δ15N)), and drought resistance (turgor loss point, leaf carbon isotope composition (δ13C)) were measured. Then, plants were exposed to a drought treatment and possible shifts in photosynthetic performance were monitored using chlorophyll fluorescence. Inoculated plants exhibited significantly greater germination than controls regardless of family. The inoculation treatment significantly increased root:shoot biomass ratio in the wet family but not in the dry family, suggesting soil microbes alter functional traits that improve water and nutrient uptake more so in a family originating from a wetter climate than in a family originating from a drier climate. Microbial effects on photosynthetic performance during drought also differed between families, as photosynthetic performance of the dry inoculated group declined fastest. Regardless of treatment, the dry family exhibited a greater root:shoot biomass ratio, root exudate concentration, and leaf δ15N than the wet family. This indicates that the dry family allocated more resources belowground than the wet and the two family may have used different sources of plant available N, which may be related to their contrasting climates of origin and influence their drought resistance. Examination of variation in impacts of soil microbes on seedling physiology improves efforts to enhance seedling establishment and beneficial plant-microbe interactions under climate change.
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Affiliation(s)
| | - Sanna Sevanto
- Earth and Environmental Sciences (EES-14), Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Samantha Peterson
- Earth and Environmental Sciences Department, New Mexico Institute of Mining and Technology, Socorro, NM, United States
| | - Max Ryan
- Earth and Environmental Sciences (EES-14), Los Alamos National Laboratory, Los Alamos, NM, United States
| | - John Dunbar
- Bioscience (B-11), Los Alamos National Laboratory, Los Alamos, NM, United States
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17
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Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration. Proc Natl Acad Sci U S A 2019; 116:6193-6198. [PMID: 30858310 DOI: 10.1073/pnas.1815107116] [Citation(s) in RCA: 105] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in the western United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States.
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