Historical and projected trends in landscape drivers affecting carbon dynamics in Alaska

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.

Assessing historical and projected carbon balance of Alaska: A synthesis of results and policy/management implications

“…The distribution of wetland and upland ecosystems in Alaska was defined by upscaling a random subset of the National Wetlands Inventory (see Pastick et al. ). The distribution of inland aquatic ecosystems in Alaska was defined from the National Hydrography Database (see Stackpoole et al.…”

“…The historical and future climate and fire disturbance data sets, as well as data syntheses for permafrost distribution, are described in Pastick et al. (); analyses of biogeochemical cycling are described for uplands in Genet et al. () and for wetlands in Lyu et al.…”

“…ALFRESCO was calibrated on the basis of historical data about fire occurrence for Alaska from 1950 through 2009 (see Pastick et al. for more details). The contemporary spatial distribution of permafrost was estimated by two different empirical approaches.…”

“…This paper of the invited feature synthesizes the overall results from a recent collaborative and integrated Alaska carbon assessment (reported in Zhu and McGuire ) and the various components of the assessment including analysis of driving factors of carbon dynamics (Pastick et al. ), and syntheses of carbon dynamics across upland ecosystems (Genet et al. ), wetland ecosystems (Lyu et al.…”

Differences in Human versus Lightning Fires between Urban and Rural Areas of the Boreal Forest in Interior Alaska

“…Models predict continued increases in area burned and carbon emissions in boreal North America in the future [11][12][13][14] in response to a strengthening of arctic amplification of global climate change [15]. However, there are indications of an ecosystem shift from highly flammable mature spruce to less flammable early successional deciduous vegetation [16][17][18][19].…”