288 results on '"McGuire, A. David"'
Search Results
252. ESTIMATES OF LARGE-SCALE FLUXES IN HIGH LATITUDES FROM TERRESTRIAL BIOSPHERE MODELS AND AN INVERSION OF ATMOSPHERIC CO[sub 2] MEASUREMENTS.
- Author
-
Dargaville, Roger, McGuire, A. David, and Rayner, Peter
- Subjects
CARBON ,TAIGAS ,CLIMATE change - Abstract
Focuses on the importance of improving the estimates of large-scale carbon fluxes over the boreal forest. Magnitude of climate change; Derivation of atmospheric transport model from a set of observations on atmospheric carbon dioxide concentrations; Need for terrestrial biosphere models to be developed.
- Published
- 2002
- Full Text
- View/download PDF
253. Temporal uncertainties of integrated ecological/economic assessments at the global and regional scales.
- Author
-
Perez-Garcia, John, Joyce, Linda A., and McGuire, A. David
- Subjects
FOREST microclimatology ,CLIMATE change ,DECISION making - Abstract
Over the past several years, research using the Center for International Trade in Forest Products (CINTRAFOR) Global Trade Model (CGTM) and the Terrestrial Ecosystem Model (TEM) has estimated the potential effects of climate change on the global forest sector. The process of linking these two models—many model runs with alternative economic, ecological and climate scenarios—provides useful information on (i) the behavior of the economic model under alternative assumptions, (ii) integrated economic/ecological results and (iii) their implication for decision makers. Previous works indicate that assumptions on economic behavior and ecology interactions are important when estimating the economic effects of climate change on the forest sector. This paper estimates the economic effects associated with alternative transient paths of change in climate and CO
2 on the forest sector. The results indicate economic welfare measures change significantly under two alternative assumptions of the path that changes in climate and CO2 may take. An assumption of a pseudo-transient constant rate of change to reach an equilibrium endpoint produces larger global welfare changes over the time period than a “true” transient change in climate by an average US$ 2 billion over the period 1994–2040. In addition, regional and market segment impacts are not uniformly distributed and should also be considered when programmatic needs are identified. [Copyright &y& Elsevier]- Published
- 2002
- Full Text
- View/download PDF
254. A first-order analysis of the potential rôle of CO2 fertilization to affect the global carbon budget: a comparison of four terrestrial biosphere models.
- Author
-
KICKLIGHTER, DAVID W., BRUNO, MICHELE, DÖNGES, SILKE, ESSER, GERD, HEIMANN, MARTIN, HELFRICH, JOHN, IFT, FRANK, JOOS, FORTUNAT, KADUK, JÖRG, KOHLMAIER, GUNDOLF H., McGUIRE, A. DAVID, MELILLO, JERRY M., MEYER, ROBERT, III, BERRIEN MOORE, NADLER, ANDREAS, PRENTICE, I. COLIN, SAUF, WALTER, SCHLOSS, ANNETTE L., SITCH, STEPHEN, and WITTENBERG, UWE
- Published
- 1999
- Full Text
- View/download PDF
255. The importance of climate and soils for estimates of net primary production: a sensitivity analysis with the terrestrial ecosystem model.
- Author
-
Melillo, Jerry M., McGuire, A. David, Pan, Yude, and Kicklighter, David W.
- Subjects
- *
BIOTIC communities , *SOILS , *SOLAR radiation - Published
- 1996
256. On the influence of biomass burning on the seasonal CO2 Signal as observed at monitoring stations.
- Author
-
Wittenberg, Uwe, Heimann, Martin, Esser, Gerd, McGuire, A. David, and Sauf, Walter
- Published
- 1998
- Full Text
- View/download PDF
257. Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP).
- Author
-
Pan, Yude, Melillo, Jerry M., McGuire, A. David, Kicklighter, David W., Pitelka, Louis F., Hibbard, Kathy, Pierce, Lars L., Running, Steven W., Ojima, Dennis S., Parton, William J., and Schimel, David S.
- Abstract
Although there is a great deal of information concerning responses to increases in atmospheric CO
2 at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO2 is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO2 . In this study, we analyze the responses of net primary production (NPP) to doubled CO2 from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO2 causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO2 and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO2 for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO2 for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO2 is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO2 is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO2 is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO2 . [ABSTRACT FROM AUTHOR]- Published
- 1998
- Full Text
- View/download PDF
258. A first-order analysis of the potential rôle of CO2fertilization to affect the global carbon budget: a comparison of four terrestrial biosphere models
- Author
-
Kicklighter, David W., Bruno, Michele, DZönges, Silke, Esser, Gerd, Heimann, Martin, Helfrich, John, Ift, Frank, Joos, Fortunat, Kaduk, Jörg, Kohlmaier, Gundolf H., McGuire, A. David, Melillo, Jerry M., Meyer, Robert, III, Berrien Moore, Nadler, Andreas, Prentice, I. Colin, Sauf, Walter, Schloss, Annette L., Sitch, Stephen, Wittenberg, Uwe, and Würth, Gudrun
- Abstract
We compared the simulated responses of net primary production, heterotrophic respiration, net ecosystem production and carbon storage in natural terrestrial ecosystems to historical (1765 to 1990) and projected (1990–2300) changes of atmospheric CO2concentration of four terrestrial biosphere models: the Bern model, the Frankfurt Biosphere Model (FBM), the High-Resolution Biosphere Model (HRBM) and the Terrestrial EcosystemModel (TEM). The results of the model intercomparison suggest that CO2fertilization of natural terrestrial vegetation has the potential to account for a large fraction of the so-called “missing carbon sink” of 2.0 Pg C in 1990. Estimates of this potential are reduced when the models incorporate the concept that CO2fertilization can be limited by nutrient availability. Although the model estimates differ on the potential size (126 to 461 Pg C) of the future terrestrial sink caused by CO2fertilization, the results of the four models suggest that natural terrestrial ecosystems will have a limited capacity to act as a sink of atmospheric CO2in the future as a result of physiological constraints and nutrient constraints on NPP. All the spatially explicit models estimate a carbon sink in both tropical and northern temperate regions, but the strength of these sinks varies over time. Differences in the simulated response of terrestrial ecosystems to CO2fertilization among the models in this intercomparison study reflect the fact that the models have highlighted different aspects of the effect of CO2fertilization on carbon dynamics of natural terrestrial ecosystems including feedback mechanisms. As interactions with nitrogen fertilization, climate change and forest regrowth may play an important role in simulating the response of terrestrial ecosystems to CO2fertilization, these factors should be included in future analyses. Improvements in spatially explicit data sets, whole-ecosystem experiments and the availability of net carbon exchange measurements across the globe will also help to improve future evaluations of the role of CO2fertilization on terrestrial carbon storage.
- Published
- 1999
- Full Text
- View/download PDF
259. STUDIES ON EXPERIMENTAL SHIGELLOSIS
- Author
-
McGuire, C. David and Floyd, Thomas M.
- Abstract
Host resistance to Shigella infections can be decreased by non-specific physical stress. Fasting lowers the number of Shigella required for a parenteral LD50 dose. While the LD50 by the oral route is larger in fasted than in nonfasted animals, the fasted host's susceptibility to oral infection is increased as evidenced by the increased fecal Shigella carrier state, duration of intestinal infection, and increased incidence of Shigella bacteriemia. Fatigue also increases the animal's susceptibility to shigellosis, but to a lesser extent than does fasting.
- Published
- 1958
- Full Text
- View/download PDF
260. Identification of Group A Streptococci: Bacitracin Disc and Fluorescent Antibody Techniques Compared with the Lancefield Precipitin Method
- Author
-
STREAMER, CHARLES W., WILLIAMS, PAUL M., LOU WANG, WEN LAN, JOHNSON, R. SAMUEL, McGUIRE, C. DAVID, ABELOW, IRENE J., and GLASER, ROBERT J.
- Abstract
During the course of a project which had as its primary objective the evaluation of a streptococcal disease control program,1 an opportunity was presented to compare the efficacy of (a) the bacitracin disc method and (b) the fluorescent antibody method of identifying Group A streptococci with the Lancefield precipitin technique. The results which were obtained and are here presented are confirmatory of previous work2,3 and show that both the bacitracin disc and the fluorescent antibody techniques are highly reliable. Each, therefore, represents a useful method for the identification of Group A streptococci in clinical laboratories. METHODS A total of 776 strains of streptococci was subjected to study; 669 (90%) were isolated from patients who were seen on the clinical services of the Denver General Hospital, while 69 strains (10%) were obtained from household contacts of patients included in the study. Of the streptococcal isolations, 76% were made from
- Published
- 1962
- Full Text
- View/download PDF
261. Author Correction: Large loss of CO2in winter observed across the northern permafrost region
- Author
-
Natali, Susan M., Watts, Jennifer D., Rogers, Brendan M., Potter, Stefano, Ludwig, Sarah M., Selbmann, Anne-Katrin, Sullivan, Patrick F., Abbott, Benjamin W., Arndt, Kyle A., Birch, Leah, Björkman, Mats P., Bloom, A. Anthony, Celis, Gerardo, Christensen, Torben R., Christiansen, Casper T., Commane, Roisin, Cooper, Elisabeth J., Crill, Patrick, Czimczik, Claudia, Davydov, Sergey, Du, Jinyang, Egan, Jocelyn E., Elberling, Bo, Euskirchen, Eugenie S., Friborg, Thomas, Genet, Hélène, Göckede, Mathias, Goodrich, Jordan P., Grogan, Paul, Helbig, Manuel, Jafarov, Elchin E., Jastrow, Julie D., Kalhori, Aram A. M., Kim, Yongwon, Kimball, John S., Kutzbach, Lars, Lara, Mark J., Larsen, Klaus S., Lee, Bang-Yong, Liu, Zhihua, Loranty, Michael M., Lund, Magnus, Lupascu, Massimo, Madani, Nima, Malhotra, Avni, Matamala, Roser, McFarland, Jack, McGuire, A. David, Michelsen, Anders, Minions, Christina, Oechel, Walter C., Olefeldt, David, Parmentier, Frans-Jan W., Pirk, Norbert, Poulter, Ben, Quinton, William, Rezanezhad, Fereidoun, Risk, David, Sachs, Torsten, Schaefer, Kevin, Schmidt, Niels M., Schuur, Edward A. G., Semenchuk, Philipp R., Shaver, Gaius, Sonnentag, Oliver, Starr, Gregory, Treat, Claire C., Waldrop, Mark P., Wang, Yihui, Welker, Jeffrey, Wille, Christian, Xu, Xiaofeng, Zhang, Zhen, Zhuang, Qianlai, and Zona, Donatella
- Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2019
- Full Text
- View/download PDF
262. Reduced arctic tundra productivity linked with landform and climate change interactions
- Author
-
Lara, Mark J., Nitze, Ingmar, Grosse, Guido, Martin, Philip, and McGuire, A. David
- Subjects
13. Climate action ,15. Life on land - Abstract
Arctic tundra ecosystems have experienced unprecedented change associated with climate warming over recent decades. Across the Pan-Arctic, vegetation productivity and surface greenness have trended positively over the period of satellite observation. However, since 2011 these trends have slowed considerably, showing signs of browning in many regions. It is unclear what factors are driving this change and which regions/landforms will be most sensitive to future browning. Here we provide evidence linking decadal patterns in arctic greening and browning with regional climate change and local permafrost-driven landscape heterogeneity. We analyzed the spatial variability of decadal-scale trends in surface greenness across the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) using the Landsat archive (1999-2014), in combination with novel 30 m classifications of polygonal tundra and regional watersheds, finding landscape heterogeneity and regional climate change to be the most important factors controlling historical greenness trends. Browning was linked to increased temperature and precipitation, with the exception of young landforms (developed following lake drainage), which will likely continue to green. Spatiotemporal model forecasting suggests carbon uptake potential to be reduced in response to warmer and/or wetter climatic conditions, potentially increasing the net loss of carbon to the atmosphere, at a greater degree than previously expected., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 550
263. Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment
- Author
-
Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., Pokrovsky, Oleg S., Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., and Pokrovsky, Oleg S.
- Abstract
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
264. Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment
- Author
-
Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., Pokrovsky, Oleg S., Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., and Pokrovsky, Oleg S.
- Abstract
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
265. Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment
- Author
-
Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., Pokrovsky, Oleg S., Abbott, Benjamin W., Jones, Jeremy B., Schuur, Edward A. G., Chapin, F. Stuart, III, Bowden, William B., Bret-Harte, M. Syndonia, Epstein, Howard E., Flannigan, Michael D., Harms, Tamara K., Hollingsworth, Teresa N., McGuire, A. David, Natali, Susan M., Rocha, Adrian V., and Pokrovsky, Oleg S.
- Abstract
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
266. Serological and Bacteriological Investigations of an Outbreak of Plague in an Urban Tree Squirrel Population
- Author
-
Hudson, Bruce W., primary, Goldenberg, Martin I., additional, McCluskie, J. Douglas, additional, Larson, Harvard E., additional, Barnes, Allan M., additional, McGuire, C. David, additional, and Poland, Jack D., additional
- Published
- 1971
- Full Text
- View/download PDF
267. IN VIVO CHANGE OF SEROLOGICAL SPECIFICITY IN SHIGELLA FLEXNERI
- Author
-
McGuire, C. David, primary and Floyd, Thomas M., additional
- Published
- 1958
- Full Text
- View/download PDF
268. Comparison of pigeon guillemot, Cepphus columba, blood parameters from oiled and unoiled areas of Alaska eight years after the Exxon Valdez oil spill
- Author
-
Litzow, M. A., Golet, G. H., Duffy, L. K., Roby, D. D., McGuire, A. David, and Seiser, P. E.
- Subjects
BIRDS ,HEMATOLOGY ,MARINE pollution ,OIL spills - Abstract
In 1997, we compared the haematological and plasma biochemical profiles among populations of pigeon guillemots, Cepphus columba, in areasoiled and not oiled by the 1989 Exxon Valdez oil spill (EVOS) that occurred in Prince William Sound (PWS), Alaska. Pigeon guillemot populations in PWS were injured by EVOS and have not returned to pre-spilllevels. If oil contamination is limiting recovery of pigeon guillemots in PWS, then we expected that blood parameters of pigeon guillemots would differ between oiled and unoiled areas and that these differences would be consistent with either toxic responses or lower fitness. We collected blood samples from chicks at approximately 20 and 30 days after hatching. Physiological changes associated with chick growth were noted in several blood parameters. We found that only calcium and mean cell volume were significantly different between the chicks in oiled and unoiled areas. Despite these differences, blood biomarkers provided little evidence of continuing oil injury to pigeon guillemot chicks, eight years after the EVOS. Preliminary data from adults indicated elevated aspartate aminotransferase activity in the adults from the oiled area, which is consistent with hepatocellular injury. Because adults have greater opportunities for exposure to residual oil than nestlings, we recommend studies that fully evaluate the healthof adults residing in oiled areas. [ABSTRACT FROM AUTHOR]
- Published
- 2000
269. Equilibrium responses of soil carbon to climage change: empirical and process-based estimates
- Author
-
Melillo, Jerry M., McGuire, A. David, Kicklighter, David, and Joyce, Linda M.
- Subjects
BIOTIC communities ,SOILS - Published
- 1995
270. Response of plant community structure and primary productivity to experimental drought and flooding in an Alaskan fen1.
- Author
-
Churchill, Amber C., Turetsky, Merritt R., McGuire, A. David, and Hollingsworth, Teresa N.
- Subjects
- *
FENS , *PLANT communities , *PLANT anatomy , *PLANT productivity , *EFFECT of drought on plants , *EFFECT of floods on plants , *ATMOSPHERIC carbon dioxide , *CARBON cycle - Abstract
Northern peatlands represent a long-term net sink for atmospheric CO2, but these ecosystems can shift from net carbon (C) sinks to sources based on changing climate and environmental conditions. In particular, changes in water availability associated with climate control peatland vegetation and carbon uptake processes. We examined the influence of changing hydrology on plant species abundance and ecosystem primary production in an Alaskan fen by manipulating the water table in field treatments to mimic either sustained flooding (raised water table) or drought (lowered water table) conditions for 6 years. We found that water table treatments altered plant species abundance by increasing sedge and grass cover in the raised water table treatment and reducing moss cover while increasing vascular green area in the lowered water table treatment. Gross primary productivity was lower in the lowered treatment than in the other plots, although there were no differences in total biomass or vascular net primary productivity among the treatments. Overall, our results indicate that vegetation abundance was more sensitive to variation in water table than total biomass and vascular biomass accrual. Finally, in our experimental peatland, drought had stronger consequences for change in vegetation abundance and ecosystem function than sustained flooding. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
271. Soil carbon distribution in Alaska in relation to soil-forming factors
- Author
-
Johnson, Kristofer D., Harden, Jennifer, McGuire, A. David, Bliss, Norman B., Bockheim, James G., Clark, Mark, Nettleton-Hollingsworth, Teresa, Jorgenson, M. Torre, Kane, Evan S., Mack, Michelle, O'Donnell, Jonathan, Ping, Chien-Lu, Schuur, Edward A.G., Turetsky, Merritt R., and Valentine, David W.
- Subjects
- *
SOIL formation , *CARBON in soils , *CLIMATE change , *LANDSCAPES , *BIOTIC communities , *CHEMICAL decomposition , *PERMAFROST - Abstract
Abstract: The direction and magnitude of soil organic carbon (SOC) changes in response to climate change remain unclear and depend on the spatial distribution of SOC across landscapes. Uncertainties regarding the fate of SOC are greater in high-latitude systems where data are sparse and the soils are affected by sub-zero temperatures. To address these issues in Alaska, a first-order assessment of data gaps and spatial distributions of SOC was conducted from a recently compiled soil carbon database. Temperature and landform type were the dominant controls on SOC distribution for selected ecoregions. Mean SOC pools (to a depth of 1-m) varied by three, seven and ten-fold across ecoregion, landform, and ecosystem types, respectively. Climate interactions with landform type and SOC were greatest in the uplands. For upland SOC there was a six-fold non-linear increase in SOC with latitude (i.e., temperature) where SOC was lowest in the Intermontane Boreal compared to the Arctic Tundra and Coastal Rainforest. Additionally, in upland systems mineral SOC pools decreased as climate became more continental, suggesting that the lower productivity, higher decomposition rates and fire activity, common in continental climates, interacted to reduce mineral SOC. For lowland systems, in contrast, these interactions and their impacts on SOC were muted or absent making SOC in these environments more comparable across latitudes. Thus, the magnitudes of SOC change across temperature gradients were non-uniform and depended on landform type. Additional factors that appeared to be related to SOC distribution within ecoregions included stand age, aspect, and permafrost presence or absence in black spruce stands. Overall, these results indicate the influence of major interactions between temperature-controlled decomposition and topography on SOC in high-latitude systems. However, there remains a need for more SOC data from wetlands and boreal-region permafrost soils, especially at depths>1m in order to fully understand the effects of climate on soil carbon in Alaska. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
272. Mycobiont contribution to tundra plant acquisition of permafrost‐derived nitrogen.
- Author
-
Hewitt, Rebecca E., DeVan, M. Rae, Lagutina, Irina V., Genet, Helene, McGuire, A. David, Taylor, D. Lee, and Mack, Michelle C.
- Subjects
- *
TUNDRAS , *MYCORRHIZAL fungi , *PLANT productivity , *SOIL heating , *SOIL erosion , *HOST plants - Abstract
Summary: As Arctic soils warm, thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon losses from tundra ecosystems. Although mycorrhizal fungi could facilitate plant access to permafrost‐derived N, their exploration capacity beyond host plant root systems into deep, cold active layer soils adjacent to the permafrost table is unknown.We characterized root‐associated fungi (RAF) that colonized ericoid (ERM) and ectomycorrhizal (ECM) shrub roots and occurred below the maximum rooting depth in permafrost thaw‐front soil in tussock and shrub tundra communities. We explored the relationships between root and thaw front fungal composition and plant uptake of a 15N tracer applied at the permafrost boundary.We show that ERM and ECM shrubs associate with RAF at the thaw front providing evidence for potential mycelial connectivity between roots and the permafrost boundary. Among shrubs and tundra communities, RAF connectivity to the thaw boundary was ubiquitous. The occurrence of particular RAF in both roots and thaw front soil was positively correlated with 15N recovered in shrub biomassTaxon‐specific RAF associations could be a mechanism for the vertical redistribution of deep, permafrost‐derived nutrients, which may alleviate N limitation and stimulate productivity in warming tundra. See also the Commentary on this article by Robinson et al., (2020), 226: 8–10. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
273. Soil moisture and hydrology projections of the permafrost region – a model intercomparison.
- Author
-
Andresen, Christian G., Lawrence, David M., Wilson, Cathy J., McGuire, A. David, Koven, Charles, Schaefer, Kevin, Jafarov, Elchin, Peng, Shushi, Chen, Xiaodong, Gouttevin, Isabelle, Burke, Eleanor, Chadburn, Sarah, Ji, Duoying, Chen, Guangsheng, Hayes, Daniel, and Zhang, Wenxin
- Subjects
- *
HYDROLOGY , *PERMAFROST , *RUNOFF models , *TUNDRAS , *SOIL moisture , *WATERSHEDS - Abstract
This study investigates and compares soil moisture and hydrology projections of broadly used land models with permafrost processes and highlights the causes and impacts of permafrost zone soil moisture projections. Climate models project warmer temperatures and increases in precipitation (P) which will intensify evapotranspiration (ET) and runoff in land models. However, this study shows that most models project a long-term drying of the surface soil (0–20 cm) for the permafrost region despite increases in the net air–surface water flux (P -ET). Drying is generally explained by infiltration of moisture to deeper soil layers as the active layer deepens or permafrost thaws completely. Although most models agree on drying, the projections vary strongly in magnitude and spatial pattern. Land models tend to agree with decadal runoff trends but underestimate runoff volume when compared to gauge data across the major Arctic river basins, potentially indicating model structural limitations. Coordinated efforts to address the ongoing challenges presented in this study will help reduce uncertainty in our capability to predict the future Arctic hydrological state and associated land–atmosphere biogeochemical processes across spatial and temporal scales. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
274. Positive biodiversity-productivity relationship predominant in global forests.
- Author
-
Jingjing Liang, Crowther, Thomas W., Picard, Nicolas, Wiser, Susan, Mo Zhou, Alberti, Giorgio, Schulze, Ernst-Detlef, McGuire, A. David, Bozzato, Fabio, Pretzsch, Hans, de-Miguel, Sergio, Paquette, Alain, Hérault, Bruno, Scherer-Lorenzen, Michael, Barrett, Christopher B., Glick, Henry B., Hengeveld, Geerten M., Nabuurs, Gert-Jan, Pfautsch, Sebastian, and Viana, Helder
- Subjects
- *
ECOSYSTEMS , *BIODIVERSITY conservation , *FOREST productivity & climate , *FOREST management , *BIOMES - Abstract
The biodiversity-productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, showing that continued biodiversity loss would result in an accelerating decline in forest productivity worldwide.The value of biodiversity in maintaining commercial forest productivity alone—US$166 billion to 490 billion per year according to our estimation—is more than twice what it would cost to implement effective global conservation.This highlights the need for a worldwide reassessment of biodiversity values, forest management strategies, and conservation priorities. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
275. Resilience and sensitivity of ecosystem carbon stocks to fire-regime change in Alaskan tundra.
- Author
-
Chen, Yaping, Kelly, Ryan, Genet, Hélène, Lara, Mark Jason, Chipman, Melissa Lynn, McGuire, A. David, and Hu, Feng Sheng
- Published
- 2022
- Full Text
- View/download PDF
276. A Large and Persistent Carbon Sink in the World's Forests.
- Author
-
Pan, Yude, Birdsey, Richard A., Jingyun Fang, Houghton, Richard, Kauppi, Pekka E., Kurz, Werner A., Phillips, Oliver L., Shvidenko, Anatoly, Lewis, Simon L., Canadell, Josep G., Ciais, Philippe, Jackson, Robert B., Pacala, Stephen W., McGuire, A. David, Piao, Shilong, Rautiainen, Aapo, Sitch, Stephen, and Hayes, Daniel
- Subjects
- *
FOREST ecology , *CARBON dioxide sinks , *CARBON cycle , *FORESTS & forestry & the environment , *FOREST biomass , *CARBON content of plant biomass , *FOREST soils , *CARBON in soils - Abstract
The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year-1) globally for 1990 to 2007 We also estimate a source of 1.3 ± 0.7 Pg C year-1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C-1 year partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year-1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year-1 with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
277. Regional carbon dynamics in monsoon Asia and its implications for the global carbon cycle
- Author
-
Tian, Hanqin, Melillo, Jerry M., Kicklighter, David W., Pan, Shufen, Liu, Jiyuan, McGuire, A. David, and Moore III, Berrien
- Subjects
- *
CARBON , *BIOTIC communities - Abstract
Data on three major determinants of the carbon storage in terrestrial ecosystems are used with the process-based Terrestrial Ecosystem Model (TEM) to simulate the combined effect of climate variability, increasing atmospheric CO2 concentration, and cropland establishment and abandonment on the exchange of CO2 between the atmosphere and monsoon Asian ecosystems. During 1860–1990, modeled results suggest that monsoon Asia as a whole released 29.0 Pg C, which represents 50% of the global carbon release for this period. Carbon release varied across three subregions: East Asia (4.3 Pg C), South Asia (6.6 Pg C), and Southeast Asia (18.1 Pg C). For the entire region, the simulations indicate that land-use change alone has led to a loss of 42.6 Pg C. However, increasing CO2 and climate variability have added carbon to terrestrial ecosystems to compensate for 23% and 8% of the losses due to land-use change, respectively. During 1980–1989, monsoon Asia as a whole acted as a source of carbon to the atmosphere, releasing an average of 0.158 Pg C per year. Two of the subregions acted as net carbon source and one acted as a net carbon sink. Southeast Asia and South Asia were sources of 0.288 and 0.02 Pg C per year, respectively, while East Asia was a sink of 0.149 Pg C per year. Substantial interannual and decadal variations occur in the annual net carbon storage estimated by TEM due to comparable variations in summer precipitation and its effect on net primary production (NPP). At longer time scales, land-use change appears to be the important control on carbon dynamics in this region. [Copyright &y& Elsevier]
- Published
- 2003
- Full Text
- View/download PDF
278. Contribution of Increasing CO[sub 2] and Climate to Carbon Storage by Ecosystems in the United States.
- Author
-
Schime, David, Melillo, Jerry, Tian, Hanqin, McGuire, A. David, Kicklighter, David, Kittel, Timothy, Rosenbloom, Nan, Running, Steven, Thornton, Peter, Ojima, Dennis, Patton, William, Kelly, Robin, Sykes, Martin, Neilson, Ron, and Rizzo, Brian
- Subjects
- *
CARBON dioxide , *BIOTIC communities , *CLIMATOLOGY - Abstract
Presents information on a study which examined the effects of climate and increasing carbon dioxide on net carbon storage in terrestrial ecosystems in the United States from 1895-1993. Description of ecosystem models; Implications of high variability of net carbon storage.
- Published
- 2000
279. Large loss of CO 2 in winter observed across the northern permafrost region.
- Author
-
Natali SM, Watts JD, Rogers BM, Potter S, Ludwig SM, Selbmann AK, Sullivan PF, Abbott BW, Arndt KA, Birch L, Björkman MP, Bloom AA, Celis G, Christensen TR, Christiansen CT, Commane R, Cooper EJ, Crill P, Czimczik C, Davydov S, Du J, Egan JE, Elberling B, Euskirchen ES, Friborg T, Genet H, Göckede M, Goodrich JP, Grogan P, Helbig M, Jafarov EE, Jastrow JD, Kalhori AAM, Kim Y, Kimball J, Kutzbach L, Lara MJ, Larsen KS, Lee BY, Liu Z, Loranty MM, Lund M, Lupascu M, Madani N, Malhotra A, Matamala R, McFarland J, McGuire AD, Michelsen A, Minions C, Oechel WC, Olefeldt D, Parmentier FW, Pirk N, Poulter B, Quinton W, Rezanezhad F, Risk D, Sachs T, Schaefer K, Schmidt NM, Schuur EAG, Semenchuk PR, Shaver G, Sonnentag O, Starr G, Treat CC, Waldrop MP, Wang Y, Welker J, Wille C, Xu X, Zhang Z, Zhuang Q, and Zona D
- Abstract
Recent warming in the Arctic, which has been amplified during the winter
1-3 , greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2 )4 . However, the amount of CO2 released in winter is highly uncertain and has not been well represented by ecosystem models or by empirically-based estimates5,6 . Here we synthesize regional in situ observations of CO2 flux from arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1662 Tg C yr-1 from the permafrost region during the winter season (October through April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (-1032 Tg C yr-1 ). Extending model predictions to warmer conditions in 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario-Representative Concentration Pathway (RCP) 4.5-and 41% under business-as-usual emissions scenario-RCP 8.5. Our results provide a new baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions.- Published
- 2019
- Full Text
- View/download PDF
280. The role of environmental driving factors in historical and projected carbon dynamics of wetland ecosystems in Alaska.
- Author
-
Lyu Z, Genet H, He Y, Zhuang Q, McGuire AD, Bennett A, Breen A, Clein J, Euskirchen ES, Johnson K, Kurkowski T, Pastick NJ, Rupp TS, Wylie BK, and Zhu Z
- Subjects
- Alaska, Carbon Dioxide, Forecasting, Methane, Wildfires, Carbon Cycle, Global Warming, Models, Theoretical, Wetlands
- Abstract
Wetlands are critical terrestrial ecosystems in Alaska, covering ~177,000 km
2 , an area greater than all the wetlands in the remainder of the United States. To assess the relative influence of changing climate, atmospheric carbon dioxide (CO2 ) concentration, and fire regime on carbon balance in wetland ecosystems of Alaska, a modeling framework that incorporates a fire disturbance model and two biogeochemical models was used. Spatially explicit simulations were conducted at 1-km resolution for the historical period (1950-2009) and future projection period (2010-2099). Simulations estimated that wetland ecosystems of Alaska lost 175 Tg carbon (C) in the historical period. Ecosystem C storage in 2009 was 5,556 Tg, with 89% of the C stored in soils. The estimated loss of C as CO2 and biogenic methane (CH4 ) emissions resulted in wetlands of Alaska increasing the greenhouse gas forcing of climate warming. Simulations for the projection period were conducted for six climate change scenarios constructed from two climate models forced under three CO2 emission scenarios. Ecosystem C storage averaged among climate scenarios increased 3.94 Tg C/yr by 2099, with variability among the simulations ranging from 2.02 to 4.42 Tg C/yr. These increases were driven primarily by increases in net primary production (NPP) that were greater than losses from increased decomposition and fire. The NPP increase was driven by CO2 fertilization (~5% per 100 parts per million by volume increase) and by increases in air temperature (~1% per °C increase). Increases in air temperature were estimated to be the primary cause for a projected 47.7% mean increase in biogenic CH4 emissions among the simulations (~15% per °C increase). Ecosystem CO2 sequestration offset the increase in CH4 emissions during the 21st century to decrease the greenhouse gas forcing of climate warming. However, beyond 2100, we expect that this forcing will ultimately increase as wetland ecosystems transition from being a sink to a source of atmospheric CO2 because of (1) decreasing sensitivity of NPP to increasing atmospheric CO2 , (2) increasing availability of soil C for decomposition as permafrost thaws, and (3) continued positive sensitivity of biogenic CH4 emissions to increases in soil temperature., (© 2018 by the Ecological Society of America.)- Published
- 2018
- Full Text
- View/download PDF
281. Assessing historical and projected carbon balance of Alaska: A synthesis of results and policy/management implications.
- Author
-
McGuire AD, Genet H, Lyu Z, Pastick N, Stackpoole S, Birdsey R, D'Amore D, He Y, Rupp TS, Striegl R, Wylie BK, Zhou X, Zhuang Q, and Zhu Z
- Subjects
- Alaska, Environmental Policy, Forecasting, Carbon Cycle, Climate Change, Ecosystem
- Abstract
We summarize the results of a recent interagency assessment of land carbon dynamics in Alaska, in which carbon dynamics were estimated for all major terrestrial and aquatic ecosystems for the historical period (1950-2009) and a projection period (2010-2099). Between 1950 and 2009, upland and wetland (i.e., terrestrial) ecosystems of the state gained 0.4 Tg C/yr (0.1% of net primary production, NPP), resulting in a cumulative greenhouse gas radiative forcing of 1.68 × 10
-3 W/m2 . The change in carbon storage is spatially variable with the region of the Northwest Boreal Landscape Conservation Cooperative (LCC) losing carbon because of fire disturbance. The combined carbon transport via various pathways through inland aquatic ecosystems of Alaska was estimated to be 41.3 Tg C/yr (17% of terrestrial NPP). During the projection period (2010-2099), carbon storage of terrestrial ecosystems of Alaska was projected to increase (22.5-70.0 Tg C/yr), primarily because of NPP increases of 10-30% associated with responses to rising atmospheric CO2 , increased nitrogen cycling, and longer growing seasons. Although carbon emissions to the atmosphere from wildfire and wetland CH4 were projected to increase for all of the climate projections, the increases in NPP more than compensated for those losses at the statewide level. Carbon dynamics of terrestrial ecosystems continue to warm the climate for four of the six future projections and cool the climate for only one of the projections. The attribution analyses we conducted indicated that the response of NPP in terrestrial ecosystems to rising atmospheric CO2 (~5% per 100 ppmv CO2 ) saturates as CO2 increases (between approximately +150 and +450 ppmv among projections). This response, along with the expectation that permafrost thaw would be much greater and release large quantities of permafrost carbon after 2100, suggests that projected carbon gains in terrestrial ecosystems of Alaska may not be sustained. From a national perspective, inclusion of all of Alaska in greenhouse gas inventory reports would ensure better accounting of the overall greenhouse gas balance of the nation and provide a foundation for considering mitigation activities in areas that are accessible enough to support substantive deployment., (© 2018 by the Ecological Society of America.)- Published
- 2018
- Full Text
- View/download PDF
282. Dependence of the evolution of carbon dynamics in the northern permafrost region on the trajectory of climate change.
- Author
-
McGuire AD, Lawrence DM, Koven C, Clein JS, Burke E, Chen G, Jafarov E, MacDougall AH, Marchenko S, Nicolsky D, Peng S, Rinke A, Ciais P, Gouttevin I, Hayes DJ, Ji D, Krinner G, Moore JC, Romanovsky V, Schädel C, Schaefer K, Schuur EAG, and Zhuang Q
- Abstract
We conducted a model-based assessment of changes in permafrost area and carbon storage for simulations driven by RCP4.5 and RCP8.5 projections between 2010 and 2299 for the northern permafrost region. All models simulating carbon represented soil with depth, a critical structural feature needed to represent the permafrost carbon-climate feedback, but that is not a universal feature of all climate models. Between 2010 and 2299, simulations indicated losses of permafrost between 3 and 5 million km
2 for the RCP4.5 climate and between 6 and 16 million km2 for the RCP8.5 climate. For the RCP4.5 projection, cumulative change in soil carbon varied between 66-Pg C (1015 -g carbon) loss to 70-Pg C gain. For the RCP8.5 projection, losses in soil carbon varied between 74 and 652 Pg C (mean loss, 341 Pg C). For the RCP4.5 projection, gains in vegetation carbon were largely responsible for the overall projected net gains in ecosystem carbon by 2299 (8- to 244-Pg C gains). In contrast, for the RCP8.5 projection, gains in vegetation carbon were not great enough to compensate for the losses of carbon projected by four of the five models; changes in ecosystem carbon ranged from a 641-Pg C loss to a 167-Pg C gain (mean, 208-Pg C loss). The models indicate that substantial net losses of ecosystem carbon would not occur until after 2100. This assessment suggests that effective mitigation efforts during the remainder of this century could attenuate the negative consequences of the permafrost carbon-climate feedback., Competing Interests: The authors declare no conflict of interest., (Copyright © 2018 the Author(s). Published by PNAS.)- Published
- 2018
- Full Text
- View/download PDF
283. Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest.
- Author
-
Melvin AM, Celis G, Johnstone JF, McGuire AD, Genet H, Schuur EAG, Rupp TS, and Mack MC
- Subjects
- Alaska, Carbon Cycle, Nitrogen Cycle, Forestry methods, Forests, Magnoliopsida, Picea, Soil chemistry
- Abstract
Increasing wildfire activity in Alaska's boreal forests has led to greater fuel-reduction management. Management has been implemented to reduce wildfire spread, but the ecological impacts of these practices are poorly known. We quantified the effects of hand-thinning and shearblading on above- and belowground stand characteristics, plant species composition, carbon (C) and nitrogen (N) pools, and soil thaw across 19 sites dominated by black spruce (Picea mariana) in interior Alaska treated 2-12 years prior to sampling. The density of deciduous tree seedlings was significantly higher in shearbladed areas compared to unmanaged forest (6.4 vs. 0.1 stems/m
2 ), and unmanaged stands exhibited the highest mean density of conifer seedlings and layers (1.4 stems/m2 ). Understory plant community composition was most similar between unmanaged and thinned stands. Shearblading resulted in a near complete loss of aboveground tree biomass C pools while thinning approximately halved the C pool size (1.2 kg C/m2 compared to 3.1 kg C/m2 in unmanaged forest). Significantly smaller soil organic layer (SOL) C and N pools were observed in shearbladed stands (3.2 kg C/m2 and 116.8 g N/m2 ) relative to thinned (6.0 kg C/m2 and 192.2 g N/m2 ) and unmanaged (5.9 kg C/m2 and 178.7 g N/m2 ) stands. No difference in C and N pool sizes in the uppermost 10 cm of mineral soil was observed among stand types. Total C stocks for measured pools was 2.6 kg C/m2 smaller in thinned stands and 5.8 kg C/m2 smaller in shearbladed stands when compared to unmanaged forest. Soil thaw depth averaged 13 cm deeper in thinned areas and 46 cm deeper in shearbladed areas relative to adjacent unmanaged stands, although variability was high across sites. Deeper soil thaw was linked to shallower SOL depth for unmanaged stands and both management types, however for any given SOL depth, thaw tended to be deeper in shearbladed areas compared to unmanaged forest. These findings indicate that fuel-reduction management alters plant community composition, C and N pools, and soil thaw depth, with consequences for ecosystem structure and function beyond those intended for fire management., (© 2017 by the Ecological Society of America.)- Published
- 2018
- Full Text
- View/download PDF
284. The role of driving factors in historical and projected carbon dynamics of upland ecosystems in Alaska.
- Author
-
Genet H, He Y, Lyu Z, McGuire AD, Zhuang Q, Clein J, D'Amore D, Bennett A, Breen A, Biles F, Euskirchen ES, Johnson K, Kurkowski T, Kushch Schroder S, Pastick N, Rupp TS, Wylie B, Zhang Y, Zhou X, and Zhu Z
- Subjects
- Alaska, Fires, Models, Biological, Seasons, Carbon Cycle, Climate Change, Ecosystem
- Abstract
It is important to understand how upland ecosystems of Alaska, which are estimated to occupy 84% of the state (i.e., 1,237,774 km
2 ), are influencing and will influence state-wide carbon (C) dynamics in the face of ongoing climate change. We coupled fire disturbance and biogeochemical models to assess the relative effects of changing atmospheric carbon dioxide (CO2 ), climate, logging and fire regimes on the historical and future C balance of upland ecosystems for the four main Landscape Conservation Cooperatives (LCCs) of Alaska. At the end of the historical period (1950-2009) of our analysis, we estimate that upland ecosystems of Alaska store ~50 Pg C (with ~90% of the C in soils), and gained 3.26 Tg C/yr. Three of the LCCs had gains in total ecosystem C storage, while the Northwest Boreal LCC lost C (-6.01 Tg C/yr) because of increases in fire activity. Carbon exports from logging affected only the North Pacific LCC and represented less than 1% of the state's net primary production (NPP). The analysis for the future time period (2010-2099) consisted of six simulations driven by climate outputs from two climate models for three emission scenarios. Across the climate scenarios, total ecosystem C storage increased between 19.5 and 66.3 Tg C/yr, which represents 3.4% to 11.7% increase in Alaska upland's storage. We conducted additional simulations to attribute these responses to environmental changes. This analysis showed that atmospheric CO2 fertilization was the main driver of ecosystem C balance. By comparing future simulations with constant and with increasing atmospheric CO2 , we estimated that the sensitivity of NPP was 4.8% per 100 ppmv, but NPP becomes less sensitive to CO2 increase throughout the 21st century. Overall, our analyses suggest that the decreasing CO2 sensitivity of NPP and the increasing sensitivity of heterotrophic respiration to air temperature, in addition to the increase in C loss from wildfires weakens the C sink from upland ecosystems of Alaska and will ultimately lead to a source of CO2 to the atmosphere beyond 2100. Therefore, we conclude that the increasing regional C sink we estimate for the 21st century will most likely be transitional., (© 2017 by the Ecological Society of America.)- Published
- 2018
- Full Text
- View/download PDF
285. Historical and projected trends in landscape drivers affecting carbon dynamics in Alaska.
- Author
-
Pastick NJ, Duffy P, Genet H, Rupp TS, Wylie BK, Johnson KD, Jorgenson MT, Bliss N, McGuire AD, Jafarov EE, and Knight JF
- Subjects
- Alaska, Carbon Sequestration, Permafrost, Carbon Cycle, Climate Change, Taiga, Temperature, Tundra
- Abstract
Modern climate change in Alaska has resulted in widespread thawing of permafrost, increased fire activity, and extensive changes in vegetation characteristics that have significant consequences for socioecological systems. Despite observations of the heightened sensitivity of these systems to change, there has not been a comprehensive assessment of factors that drive ecosystem changes throughout Alaska. Here we present research that improves our understanding of the main drivers of the spatiotemporal patterns of carbon dynamics using in situ observations, remote sensing data, and an array of modeling techniques. In the last 60 yr, Alaska has seen a large increase in mean annual air temperature (1.7°C), with the greatest warming occurring over winter and spring. Warming trends are projected to continue throughout the 21st century and will likely result in landscape-level changes to ecosystem structure and function. Wetlands, mainly bogs and fens, which are currently estimated to cover 12.5% of the landscape, strongly influence exchange of methane between Alaska's ecosystems and the atmosphere and are expected to be affected by thawing permafrost and shifts in hydrology. Simulations suggest the current proportion of near-surface (within 1 m) and deep (within 5 m) permafrost extent will be reduced by 9-74% and 33-55% by the end of the 21st century, respectively. Since 2000, an average of 678 595 ha/yr was burned, more than twice the annual average during 1950-1999. The largest increase in fire activity is projected for the boreal forest, which could result in a reduction in late-successional spruce forest (8-44%) and an increase in early-successional deciduous forest (25-113%) that would mediate future fire activity and weaken permafrost stability in the region. Climate warming will also affect vegetation communities across arctic regions, where the coverage of deciduous forest could increase (223-620%), shrub tundra may increase (4-21%), and graminoid tundra might decrease (10-24%). This study sheds light on the sensitivity of Alaska's ecosystems to change that has the potential to significantly affect local and regional carbon balance, but more research is needed to improve estimates of land-surface and subsurface properties, and to better account for ecosystem dynamics affected by a myriad of biophysical factors and interactions., (© 2017 by the Ecological Society of America.)
- Published
- 2017
- Full Text
- View/download PDF
286. Positive biodiversity-productivity relationship predominant in global forests.
- Author
-
Liang J, Crowther TW, Picard N, Wiser S, Zhou M, Alberti G, Schulze ED, McGuire AD, Bozzato F, Pretzsch H, de-Miguel S, Paquette A, Hérault B, Scherer-Lorenzen M, Barrett CB, Glick HB, Hengeveld GM, Nabuurs GJ, Pfautsch S, Viana H, Vibrans AC, Ammer C, Schall P, Verbyla D, Tchebakova N, Fischer M, Watson JV, Chen HY, Lei X, Schelhaas MJ, Lu H, Gianelle D, Parfenova EI, Salas C, Lee E, Lee B, Kim HS, Bruelheide H, Coomes DA, Piotto D, Sunderland T, Schmid B, Gourlet-Fleury S, Sonké B, Tavani R, Zhu J, Brandl S, Vayreda J, Kitahara F, Searle EB, Neldner VJ, Ngugi MR, Baraloto C, Frizzera L, Bałazy R, Oleksyn J, Zawiła-Niedźwiecki T, Bouriaud O, Bussotti F, Finér L, Jaroszewicz B, Jucker T, Valladares F, Jagodzinski AM, Peri PL, Gonmadje C, Marthy W, O'Brien T, Martin EH, Marshall AR, Rovero F, Bitariho R, Niklaus PA, Alvarez-Loayza P, Chamuya N, Valencia R, Mortier F, Wortel V, Engone-Obiang NL, Ferreira LV, Odeke DE, Vasquez RM, Lewis SL, and Reich PB
- Subjects
- Climate Change, Extinction, Biological, Biodiversity, Conservation of Natural Resources, Forests, Trees physiology
- Abstract
The biodiversity-productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, showing that continued biodiversity loss would result in an accelerating decline in forest productivity worldwide. The value of biodiversity in maintaining commercial forest productivity alone-US$166 billion to 490 billion per year according to our estimation-is more than twice what it would cost to implement effective global conservation. This highlights the need for a worldwide reassessment of biodiversity values, forest management strategies, and conservation priorities., (Copyright © 2016, American Association for the Advancement of Science.)
- Published
- 2016
- Full Text
- View/download PDF
287. Biodiversity influences plant productivity through niche-efficiency.
- Author
-
Liang J, Zhou M, Tobin PC, McGuire AD, and Reich PB
- Subjects
- Alaska, Biomass, Climate Change, Conservation of Natural Resources, Forests, Models, Theoretical, Plant Development, Poverty, Species Specificity, Trees, Biodiversity, Plant Physiological Phenomena, Plants classification
- Abstract
The loss of biodiversity is threatening ecosystem productivity and services worldwide, spurring efforts to quantify its effects on the functioning of natural ecosystems. Previous research has focused on the positive role of biodiversity on resource acquisition (i.e., niche complementarity), but a lack of study on resource utilization efficiency, a link between resource and productivity, has rendered it difficult to quantify the biodiversity-ecosystem functioning relationship. Here we demonstrate that biodiversity loss reduces plant productivity, other things held constant, through theory, empirical evidence, and simulations under gradually relaxed assumptions. We developed a theoretical model named niche-efficiency to integrate niche complementarity and a heretofore-ignored mechanism of diminishing marginal productivity in quantifying the effects of biodiversity loss on plant productivity. Based on niche-efficiency, we created a relative productivity metric and a productivity impact index (PII) to assist in biological conservation and resource management. Relative productivity provides a standardized measure of the influence of biodiversity on individual productivity, and PII is a functionally based taxonomic index to assess individual species' inherent value in maintaining current ecosystem productivity. Empirical evidence from the Alaska boreal forest suggests that every 1% reduction in overall plant diversity could render an average of 0.23% decline in individual tree productivity. Out of the 283 plant species of the region, we found that large woody plants generally have greater PII values than other species. This theoretical model would facilitate the integration of biological conservation in the international campaign against several pressing global issues involving energy use, climate change, and poverty.
- Published
- 2015
- Full Text
- View/download PDF
288. Polygonal tundra geomorphological change in response to warming alters future CO2 and CH4 flux on the Barrow Peninsula.
- Author
-
Lara MJ, McGuire AD, Euskirchen ES, Tweedie CE, Hinkel KM, Skurikhin AN, Romanovsky VE, Grosse G, Bolton WR, and Genet H
- Subjects
- Alaska, Arctic Regions, Geological Phenomena, Seasons, Carbon Cycle, Carbon Dioxide analysis, Climate Change, Methane analysis, Soil chemistry, Tundra
- Abstract
The landscape of the Barrow Peninsula in northern Alaska is thought to have formed over centuries to millennia, and is now dominated by ice-wedge polygonal tundra that spans drained thaw-lake basins and interstitial tundra. In nearby tundra regions, studies have identified a rapid increase in thermokarst formation (i.e., pits) over recent decades in response to climate warming, facilitating changes in polygonal tundra geomorphology. We assessed the future impact of 100 years of tundra geomorphic change on peak growing season carbon exchange in response to: (i) landscape succession associated with the thaw-lake cycle; and (ii) low, moderate, and extreme scenarios of thermokarst pit formation (10%, 30%, and 50%) reported for Alaskan arctic tundra sites. We developed a 30 × 30 m resolution tundra geomorphology map (overall accuracy:75%; Kappa:0.69) for our ~1800 km² study area composed of ten classes; drained slope, high center polygon, flat-center polygon, low center polygon, coalescent low center polygon, polygon trough, meadow, ponds, rivers, and lakes, to determine their spatial distribution across the Barrow Peninsula. Land-atmosphere CO2 and CH4 flux data were collected for the summers of 2006-2010 at eighty-two sites near Barrow, across the mapped classes. The developed geomorphic map was used for the regional assessment of carbon flux. Results indicate (i) at present during peak growing season on the Barrow Peninsula, CO2 uptake occurs at -902.3 10(6) gC-CO2 day(-1) (uncertainty using 95% CI is between -438.3 and -1366 10(6) gC-CO2 day(-1)) and CH4 flux at 28.9 10(6) gC-CH4 day(-1) (uncertainty using 95% CI is between 12.9 and 44.9 10(6) gC-CH4 day(-1)), (ii) one century of future landscape change associated with the thaw-lake cycle only slightly alter CO2 and CH4 exchange, while (iii) moderate increases in thermokarst pits would strengthen both CO2 uptake (-166.9 10(6) gC-CO2 day(-1)) and CH4 flux (2.8 10(6) gC-CH4 day(-1)) with geomorphic change from low to high center polygons, cumulatively resulting in an estimated negative feedback to warming during peak growing season., (© 2014 John Wiley & Sons Ltd.)
- Published
- 2015
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.