Patterns in Alaskan boreal forest productivity and composition - precursors of a biome shift?

Pieter S. A. Beck, Woods Hole Research Center, pbeck@whrc.org (Presenter)
Scott J. Goetz, Woods Hole Research Center, sgoetz@whrc.org
Heather Dawn Alexander, Univ. of Florida, hdalexander@ufl.edu
Michelle Cailin Mack, University of Florida, mcmack@ufl.edu
James T. Randerson, UC Irvine, Dept. of Earth System Science, jranders@uci.edu
Glenn Juday, University of Alaska, ffgpj@uaf.edu
Yufang Jin, University of California, yufang@uci.edu
Michael Loranty, WHRC, mloranty@whrc.org

Northern high latitude forest ecosystems are particularly sensitive to a biome shift during the 21st century according to global vegetation models. Profound changes in these ecosystems, which contain at least 30% of global terrestrial carbon, could substantially modify future climate. Satellite data describing gross productivity and an extensive tree-ring data set that quantifies growth in white and black spruce stands both reveal near-ubiquitous drought-induced productivity declines in interior Alaska's undisturbed boreal forests. Carbon isotope analysis of the wood supports the hypothesis of increased drought stress in recent decades in white as well as black spruce trees. If the observed trends continue, tree dispersal rates, habitat availability, and the rate of future climate change and how it changes the disturbance regime, are expected to determine where the boreal biome will undergo a gradual geographic range shift, and where a more rapid decline.

Climate change in recent decades has intensified the fire regime in interior Alaska, with extreme fire years characterized by large burns of high severity becoming more frequent. We created a chronosequence of 6 decades of vegetation regrowth following fire using a database of remotely sensed burn scars, and maps of albedo and the deciduous fraction of vegetation (i.e. the proportion of aboveground biomass in deciduous rather than evergreen vegetation) that we generated from MODIS data. Our results indicate that since the 1950s, more severely burned areas in interior Alaska have produced a vegetation cohort that is characterized by greater deciduous biomass. These findings are conform earlier plot-scale observations that increased burn severity favors the recruitment of deciduous trees in the initial years following fire. We assess the biophysical implications of a decades-long shift in successional trajectories with increased burn severity: our in situ measurements show, for example, that 50 years after burning, purely deciduous stands in interior Alaska can contain 5-fold greater aboveground biomass and 4 times higher annual net primary productivity than black spruce stands.

Presentation Type:  Poster

Session:  Global Change Impact & Vulnerability   (Tue 11:30 AM)

Associated Project(s): 

• Goetz, Scott: Quantifying Changes in Northern High Latitude Ecosystems and Associated Feedbacks to the Climate System ...details

Poster Location ID: 111