LD1-3: The strength of the carbon sink in Alaska’s boreal forest is vulnerable to vegetation- and permafrost-induced changes in fire frequency and severity.

McGuire and Rupp have assembled gridded data sets of current vegetation, historical climate (1900-2001), and the fire regime (1950-2001) in interior Alaska as part of the Western Arctic Linkage Experiment (WALE) project. They are using these data to drive a fire-climate-vegetation model (ALFRESCO) coupled to a biogeochemical model (TEM, the Terrestrial Ecosystem Model) to reconstruct a historical record of carbon storage and energy feedbacks to climate for interior Alaska. In this study we will develop data sets of projected changes in climate and other factors and extend the simulations of TEM-ALFRESCO to 2100 over interior Alaska to evaluate the vulnerability of carbon storage to vegetation- and permafrost-induced changes in fire frequency and severity.

Our projections of climate will be based on the scenarios organized by ACIA. We will choose two scenarios that represent a range in temperature and precipitation changes over the region. Because these climate change scenarios are not well matched to contemporary climate at the regional scale, we will reprocess the scenarios so they represent smooth changes from a baseline current climate; we will use a methodology similar to that used in earlier studies by McGuire. The procedure will allow us to drive TEM-ALFRESCO with a climate data set that smoothly crosses from the historical into the projected period and avoids artificial transient jumps of land cover change and carbon storage at that boundary.

One way in which we will evaluate how improved understanding of vegetation- and permafrost-induced changes in fire frequency and severity affect carbon storage in interior Alaska will be to compare carbon dynamics from a “control” version of TEM-ALFRESCO with a version that has been modified to consider improved understanding that is relevant to TEM and ALFRESCO. Specifically, the new version of TEM-ALFRESCO will incorporate understanding gained from several research activities: fire probability changes in ALFRESCO (LD1-1); fire severity effects on carbon storage in TEM (LD1-2) and post-fire succession in ALFRESCO (FD1-3 and LD1-2); and post-fire successional changes in TEM (BG2-1). We will modify TEM and ALFRESCO based on one issue at a time and then compare the control and newly modified version of TEM-ALFRESCO so that we can evaluate how to which issues carbon storage of interior Alaska is vulnerable.

To evaluate the importance of the degree to which permafrost dynamics affects carbon storage in response to a warming climate, we will conduct two simulations in which (1) permafrost and other processes respond to the warming climate and (2) permafrost responds to a detrended climate while other processes respond to a warming climate. These projections of permafrost dynamics will build on research of Romanovsky in LDF2-2. A result in which the dynamics of carbon storage varies substantially between these simulations would indicate that carbon storage is vulnerable to permafrost dynamics.