Simulated response of conterminous United States ecosystems to climate change at different levels of fire suppression, CO2 emission rate, and growth response to CO2

article i nfo Article history: Accepted 13 January 2008 Available online 16 August 2008 A modeling experiment was designed to investigate the impact of fire management, CO2 emission rate, and the growth response to CO2 on the response of ecosystems in the conterminous United States to climate scenarios produced by three different General Circulation Models (GCMs) as simulated by the MC1 Dynamic General Vegetation Model (DGVM). Distinct regional trends in response to projected climatic change were evident across all combinations of the experimental factors. In the eastern half of the U.S., the average response to relatively large increases in temperature and decreases in precipitation was an 11% loss of total ecosystem carbon. In the West, the response to increases in precipitation and relatively small increases in temperature was a 5% increase in total carbon stocks. Simulated fire suppression reduced average carbon losses in the East to about 6%, and preserved forests which were largely converted to woodland and savanna in the absence of fire suppression. Across the west, unsuppressed fire maintained near constant carbon stocks despite increases in vegetation productivity. With fire suppression, western carbon stocks increased by 10% and most shrublands were converted to woodland or even forest. With a relatively high level of growth in response to CO2, total ecosystem carbon pools at the end of the century were on average about 9-10% larger in both regions of the U.S. compared to a low CO2 response. The western U.S. gained enough carbon to counter losses from unsuppressed fire only with the high CO2 response, especially in conjunction with the higher CO2 emission rate. In the eastern U.S., fire suppression was sufficient to produce a simulated carbon sink only with both the high CO2 response and emission rate. Considerable uncertainty exists with respect to the impacts of global warming on the ecosystems of the conterminous U.S., some of which resides in the future trajectory of greenhouse gas emissions, in the direct response of vegetation to increasing CO2, and in future tradeoffs among different fire management options, as illustrated in this study.

[1]  C. Daly,et al.  Interactions between fire, grazing and climate change at Wind Cave National Park, SD , 2000 .

[2]  S. Schneider,et al.  Emissions pathways, climate change, and impacts on California. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[3]  Benjamin Smith,et al.  Simulating past and future dynamics of natural ecosystems in the United States , 2003 .

[4]  W. Bond.  Large parts of the world are brown or black: A different view on the ‘Green World’ hypothesis , 2005 .

[5]  J. Overpeck,et al.  Climate-induced changes in forest disturbance and vegetation , 1990, Nature.

[6]  R. Siegwolf,et al.  Carbon Flux and Growth in Mature Deciduous Forest Trees Exposed to Elevated CO2 , 2005, Science.

[7]  C. E. Van Wagner,et al.  Prediction of crown fire behavior in two stands of jack pine , 1993 .

[8]  Kevin C. Ryan,et al.  Modeling postfire conifer mortality for long-range planning , 1986 .

[9]  David Joseph Moore,et al.  Contrasting responses of forest ecosystems to rising atmospheric CO2: Implications for the global C cycle , 2005 .

[10]  S. Running,et al.  Impacts of climate change on natural forest productivity – evidence since the middle of the 20th century , 2006 .

[11]  R. Neilson,et al.  Simulating the response of natural ecosystems and their fire regimes to climatic variability in Alaska , 2005 .

[12]  Jack D. Cohen,et al.  The national fire-danger rating system: basic equations , 1985 .

[13]  S. Archer,et al.  Woody plant encroachment into southwestern grasslands and savannas: rates, patterns and proximate causes. , 1994 .

[14]  I. C. Prentice,et al.  Evaluation of ecosystem dynamics, plant geography and terrestrial carbon cycling in the LPJ dynamic global vegetation model , 2003 .

[15]  D. Bachelet,et al.  THE RESPONSE OF VEGETATION DISTRIBUTION, ECOSYSTEM PRODUCTIVITY, AND FIRE IN CALIFORNIA TO FUTURE CLIMATE SCENARIOS , 2005 .

[16]  D. G. Green,et al.  Fire and stability in the postglacial forests of southwest Nova Scotia , 1982 .

[17]  C. Allen,et al.  ECOLOGICAL RESTORATION OF SOUTHWESTERN PONDEROSA PINE ECOSYSTEMS: A BROAD PERSPECTIVE , 2002 .

[18]  D. Ellsworth,et al.  Functional responses of plants to elevated atmospheric CO2– do photosynthetic and productivity data from FACE experiments support early predictions? , 2004 .

[19]  W. Parton,et al.  A general model for soil organic matter dynamics: sensitivity to litter chemistry, texture and management. , 1994 .

[20]  F. Woodward,et al.  The global distribution of ecosystems in a world without fire. , 2004, The New phytologist.

[21]  Robert E. Keane,et al.  Cascading effects of fire exclusion in Rocky Mountain ecosystems: a literature review , 2002 .

[22]  A. W. Küchler.  Potential Natural Vegetation of the Conterminous United States , 1965 .

[23]  R. Ceulemans,et al.  Forest response to elevated CO2 is conserved across a broad range of productivity. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[24]  T. Swetnam,et al.  Mesoscale Disturbance and Ecological Response to Decadal Climatic Variability in the American Southwest , 1998 .

[25]  R. Neilson,et al.  Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States , 2001, Ecosystems.

[26]  T. Swetnam,et al.  Interannual to decadal drought and wildfire in the western United States , 2003 .

[27]  James S. Clark,et al.  FIRE AND CLIMATE CHANGE DURING THE LAST 750 YR IN NORTHWESTERN MINNESOTA , 1990 .

[28]  W. Parton,et al.  MC1: a dynamic vegetation model for estimating the distribution of vegetation and associated carbon, nutrients, and water—technical documentation. Version 1.0. , 2001 .

[29]  Dominique Bachelet,et al.  DYNAMIC SIMULATION OF TREE–GRASS INTERACTIONS FOR GLOBAL CHANGE STUDIES , 2000 .

[30]  C. Körner,et al.  Growth and phenology of mature temperate forest trees in elevated CO2 , 2006 .

[31]  S. Shafer,et al.  The role of climate and vegetation change in shaping past and future fire regimes in the northwestern US and the implications for ecosystem management , 2003 .

[32]  T. Swetnam,et al.  Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity , 2006, Science.

[33]  Bill Leenhouts,et al.  Assessment of Biomass Burning in the Conterminous United States , 1998 .

[34]  P. Friedlingstein,et al.  On the contribution of CO2 fertilization to the missing biospheric sink , 1995 .

[35]  Margaret M. Moore,et al.  Southwestern Ponderosa Forest Structure: Changes Since Euro-American Settlement , 1994, Journal of Forestry.

[36]  R. Neilson,et al.  Regional Differences in the Carbon Source-Sink Potential of Natural Vegetation in the U.S.A. , 2004 .

[37]  Jon E. Keeley,et al.  Fire and the Miocene expansion of C4 grasslands , 2005 .

[38]  R. Neilson,et al.  Climate change effects on vegetation distribution, carbon, and fire in California , 2003 .

[39]  W. Romme,et al.  The Interaction of Fire, Fuels, and Climate across Rocky Mountain Forests , 2004 .