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Abstract
The terrestrial biosphere is a key component of the global carbon cycle and its carbon balance is strongly influenced by climate. Continuing environmental changes are thought to increase global terrestrial carbon uptake. But evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected increase in terrestrial carbon uptake. Here we explore the mechanisms and impacts of climate extremes on the terrestrial carbon cycle, and propose a pathway to improve our understanding of present and future impacts of climate extremes on the terrestrial carbon budget.
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Liu H, Park Williams A, Allen CD, Guo D, Wu X, Anenkhonov OA, Liang E, Sandanov DV, Yin Y, Qi Z, Badmaeva NK. Rapid warming accelerates tree growth decline in semi-arid forests of Inner Asia. GLOBAL CHANGE BIOLOGY 2013; 19:2500-10. [PMID: 23564688 DOI: 10.1111/gcb.12217] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 03/26/2013] [Indexed: 05/04/2023]
Abstract
Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests.
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Affiliation(s)
- Hongyan Liu
- MOE Laboratory for Earth Surface Processes, Peking University, Beijing, China
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53
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Das AJ, Stephenson NL, Flint A, Das T, van Mantgem PJ. Climatic correlates of tree mortality in water- and energy-limited forests. PLoS One 2013; 8:e69917. [PMID: 23936118 PMCID: PMC3723662 DOI: 10.1371/journal.pone.0069917] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 06/16/2013] [Indexed: 12/04/2022] Open
Abstract
Recent increases in tree mortality rates across the western USA are correlated with increasing temperatures, but mechanisms remain unresolved. Specifically, increasing mortality could predominantly be a consequence of temperature-induced increases in either (1) drought stress, or (2) the effectiveness of tree-killing insects and pathogens. Using long-term data from California’s Sierra Nevada mountain range, we found that in water-limited (low-elevation) forests mortality was unambiguously best modeled by climatic water deficit, consistent with the first mechanism. In energy-limited (high-elevation) forests deficit models were only equivocally better than temperature models, suggesting that the second mechanism is increasingly important in these forests. We could not distinguish between models predicting mortality using absolute versus relative changes in water deficit, and these two model types led to different forecasts of mortality vulnerability under future climate scenarios. Our results provide evidence for differing climatic controls of tree mortality in water- and energy-limited forests, while highlighting the need for an improved understanding of tree mortality processes.
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Affiliation(s)
- Adrian J Das
- Western Ecological Research Center, United States Geological Survey, Three Rivers, California, United States of America.
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54
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Michelotti EA, Whicker JJ, Eisele WF, Breshears DD, Kirchner TB. Modeling aeolian transport of soil-bound plutonium: considering infrequent but normal environmental disturbances is critical in estimating future dose. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2013; 120:73-80. [PMID: 23455230 DOI: 10.1016/j.jenvrad.2013.01.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 01/08/2013] [Accepted: 01/08/2013] [Indexed: 06/01/2023]
Abstract
Dose assessments typically consider environmental systems as static through time, but environmental disturbances such as drought and fire are normal, albeit infrequent, events that can impact dose-influential attributes of many environmental systems. These phenomena occur over time frames of decades or longer, and are likely to be exacerbated under projected warmer, drier climate. As with other types of dose assessment, the impacts of environmental disturbances are often overlooked when evaluating dose from aeolian transport of radionuclides and other contaminants. Especially lacking are predictions that account for potential changing vegetation cover effects on radionuclide transport over the long time frames required by regulations. A recently developed dynamic wind-transport model that included vegetation succession and environmental disturbance provides more realistic long-term predictability. This study utilized the model to estimate emission rates for aeolian transport, and compare atmospheric dispersion and deposition rates of airborne plutonium-contaminated soil into neighboring areas with and without environmental disturbances. Specifically, the objective of this study was to utilize the model results as input for a widely used dose assessment model (CAP-88). Our case study focused on low levels of residual plutonium found in soils from past operations at Los Alamos National Laboratory (LANL), in Los Alamos, NM, located in the semiarid southwestern USA. Calculations were conducted for different disturbance scenarios based on conditions associated with current climate, and a potential future drier and warmer climate. Known soil and sediment concentrations of plutonium were used to model dispersal and deposition of windblown residual plutonium, as a function of distance and direction. Environmental disturbances that affected vegetation cover included ground fire, crown fire, and drought, with reoccurrence rates for current climate based on site historical patterns. Using site-specific meteorology, accumulation rates of plutonium in soil were modeled in a variety of directions and distances from LANL sources. Model results suggest that without disturbances, areas downwind to the contaminated watershed would accumulate LANL-derived plutonium at a relatively slow rate (<0.01 Bq m(-2) yr(-1)). However, model results under more realistic assumptions that include environmental disturbances show accumulation rates more than an order-of-magnitude faster. More generally, this assessment highlights the broader need in radioecology and environmental health physics to consider infrequent but normal environmental disturbances in longer-term dose assessments.
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Affiliation(s)
- Erika A Michelotti
- Los Alamos National Laboratory, Environmental Stewardship Group, Mail Stop J978, Los Alamos, NM 87544, USA
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55
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Moore DJP, Trahan NA, Wilkes P, Quaife T, Stephens BB, Elder K, Desai AR, Negron J, Monson RK. Persistent reduced ecosystem respiration after insect disturbance in high elevation forests. Ecol Lett 2013; 16:731-7. [PMID: 23496289 PMCID: PMC3674530 DOI: 10.1111/ele.12097] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 11/11/2012] [Accepted: 02/01/2013] [Indexed: 11/29/2022]
Abstract
Amid a worldwide increase in tree mortality, mountain pine beetles (Dendroctonus ponderosae Hopkins) have led to the death of billions of trees from Mexico to Alaska since 2000. This is predicted to have important carbon, water and energy balance feedbacks on the Earth system. Counter to current projections, we show that on a decadal scale, tree mortality causes no increase in ecosystem respiration from scales of several square metres up to an 84 km2 valley. Rather, we found comparable declines in both gross primary productivity and respiration suggesting little change in net flux, with a transitory recovery of respiration 6–7 years after mortality associated with increased incorporation of leaf litter C into soil organic matter, followed by further decline in years 8–10. The mechanism of the impact of tree mortality caused by these biotic disturbances is consistent with reduced input rather than increased output of carbon.
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Affiliation(s)
- David J P Moore
- School of Natural Resources and the Environment, University of Arizona, Biological Sciences East, Tucson, AZ 85721, USA.
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56
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Adams HD, Williams AP, Xu C, Rauscher SA, Jiang X, McDowell NG. Empirical and process-based approaches to climate-induced forest mortality models. FRONTIERS IN PLANT SCIENCE 2013; 4:438. [PMID: 24312103 PMCID: PMC3826075 DOI: 10.3389/fpls.2013.00438] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Accepted: 10/14/2013] [Indexed: 05/07/2023]
Affiliation(s)
- Henry D. Adams
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
- *Correspondence:
| | - A. Park Williams
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Chonggang Xu
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Sara A. Rauscher
- Theoretical Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Xiaoyan Jiang
- Atmospheric Chemistry Division, National Center for Atmospheric ResearchBoulder, CO, USA
| | - Nate G. McDowell
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
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57
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Breshears DD, Adams HD, Eamus D, McDowell NG, Law DJ, Will RE, Williams AP, Zou CB. The critical amplifying role of increasing atmospheric moisture demand on tree mortality and associated regional die-off. FRONTIERS IN PLANT SCIENCE 2013; 4:266. [PMID: 23935600 PMCID: PMC3731633 DOI: 10.3389/fpls.2013.00266] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 07/02/2013] [Indexed: 05/03/2023]
Affiliation(s)
- David D. Breshears
- The School of Natural Resources and the Environment, The University of ArizonaTucson, AZ, USA
- Department of Ecology and Evolutionary Biology, The University of ArizonaTucson, AZ, USA
| | - Henry D. Adams
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Derek Eamus
- School of the Environment, University of Technology SydneySydney, NSW, Australia
| | - Nate G. McDowell
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Darin J. Law
- The School of Natural Resources and the Environment, The University of ArizonaTucson, AZ, USA
- *Correspondence:
| | - Rodney E. Will
- Department of Natural Resource Ecology and Management, Oklahoma State UniversityStillwater, OK, USA
| | - A. Park Williams
- Earth and Environmental Sciences Division, Los Alamos National LaboratoryLos Alamos, NM, USA
| | - Chris B. Zou
- Department of Natural Resource Ecology and Management, Oklahoma State UniversityStillwater, OK, USA
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58
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Zeppel MJB, Anderegg WRL, Adams HD. Forest mortality due to drought: latest insights, evidence and unresolved questions on physiological pathways and consequences of tree death. THE NEW PHYTOLOGIST 2013; 197:372-374. [PMID: 23253331 DOI: 10.1111/nph.12090] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Affiliation(s)
- Melanie J B Zeppel
- Department of Biological Sciences, Centre for Climate Futures, Macquarie University, North Ryde, NSW, 2109, Australia
| | | | - Henry D Adams
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, USA
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59
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Kumagai T, Porporato A. Drought-induced mortality of a Bornean tropical rain forest amplified by climate change. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jg001835] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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60
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Long-Term Tree Cover Dynamics in a Pinyon-Juniper Woodland: Climate-Change-Type Drought Resets Successional Clock. Ecosystems 2011. [DOI: 10.1007/s10021-011-9458-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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61
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Breshears DD, López-Hoffman L, Graumlich LJ. When ecosystem services crash: preparing for big, fast, patchy climate change. AMBIO 2011; 40:256-63. [PMID: 21644454 PMCID: PMC3357807 DOI: 10.1007/s13280-010-0106-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Assessments of adaptation options generally focus on incremental, homogeneous ecosystem responses to climate even though climate change impacts can be big, fast, and patchy across a region. Regional drought-induced tree die-off in semiarid woodlands highlights how an ecosystem crash fundamentally alters most ecosystem services and poses management challenges. Building on previous research showing how choice of location is linked to adaptive capacity and vulnerability, we developed a framework showing how the options for retaining desired ecosystem services in the face of sudden crashes depend on how portable the service is and whether the stakeholder is flexible with regard to the location where they receive their services. Stakeholders using portable services, or stakeholders who can move to other locations to obtain services, may be more resilient to ecosystem crashes. Our framework suggests that entering into cooperative networks with regionally distributed stakeholders is key to building resilience to big, fast, patchy crashes.
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Affiliation(s)
- David D. Breshears
- School of Natural Resources and the Environment, The University of Arizona, 1311 E. Fourth Street, Biosciences East 325, Tucson, AZ 85721-0043 USA
- Department of Ecology and Evolutionary Biology, The University of Arizona, 1311 E. Fourth Street, Biosciences East 325, Tucson, AZ 85721-0043 USA
| | - Laura López-Hoffman
- School of Natural Resources and the Environment, The University of Arizona, 1311 E. Fourth Street, Biosciences East 325, Tucson, AZ 85721-0043 USA
- Udall Center for Studies in Public Policy, The University of Arizona, 1311 E. Fourth Street, Biosciences East 325, Tucson, AZ 85721-0043 USA
| | - Lisa J. Graumlich
- College of the Environment, The University of Washington, Seattle, WA 98195-5679 USA
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Widespread crown condition decline, food web disruption, and amplified tree mortality with increased climate change-type drought. Proc Natl Acad Sci U S A 2011; 108:1474-8. [PMID: 21220333 DOI: 10.1073/pnas.1010070108] [Citation(s) in RCA: 287] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree die-off events and contributing to the global reduction of the carbon sink efficiency of forests. There is a critical lack of integrated community-wide assessments of drought-induced responses in forests at the macroecological scale, including defoliation, mortality, and food web responses. Here we report a generalized increase in crown defoliation in southern European forests occurring during 1987-2007. Forest tree species have consistently and significantly altered their crown leaf structures, with increased percentages of defoliation in the drier parts of their distributions in response to increased water deficit. We assessed the demographic responses of trees associated with increased defoliation in southern European forests, specifically in the Iberian Peninsula region. We found that defoliation trends are paralleled by significant increases in tree mortality rates in drier areas that are related to tree density and temperature effects. Furthermore, we show that severe drought impacts are associated with sudden changes in insect and fungal defoliation dynamics, creating long-term disruptive effects of drought on food webs. Our results reveal a complex geographical mosaic of species-specific responses to climate change-driven drought pressures on the Iberian Peninsula, with an overwhelmingly predominant trend toward increased drought damage.
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63
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Forest responses to increasing aridity and warmth in the southwestern United States. Proc Natl Acad Sci U S A 2010; 107:21289-94. [PMID: 21149715 DOI: 10.1073/pnas.0914211107] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In recent decades, intense droughts, insect outbreaks, and wildfires have led to decreasing tree growth and increasing mortality in many temperate forests. We compared annual tree-ring width data from 1,097 populations in the coterminous United States to climate data and evaluated site-specific tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation by using climate records to predict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience substantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period. Using satellite imagery and aerial survey data, we conservatively calculate that ≈ 2.7% of southwestern forest and woodland area experienced substantial mortality due to wildfires from 1984 to 2006, and ≈ 7.6% experienced mortality associated with bark beetles from 1997 to 2008. We estimate that up to ≈ 18% of southwestern forest area (excluding woodlands) experienced mortality due to bark beetles or wildfire during this period. Expected climatic changes will alter future forest productivity, disturbance regimes, and species ranges throughout the Southwest. Emerging knowledge of these impending transitions informs efforts to adaptively manage southwestern forests.
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