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Above- and belowground carbon allocation in postfire lodgepole pine forests: effects of density and age.
Litton, Creighton*,1, Ryan, Michael2, Knight, Dennis1, 1 University of Wyoming, Laramie, WY2 US Department of Agriculture-Forest Service, Fort Collins, CO
ABSTRACT- We examined how carbon (C) storage and allocation varied with tree density and age in lodgepole pine stands using 16 permanent plots in Yellowstone National Park (four replicates of four forest types: low (< 103/ha), moderate (104 to 5 x 104/ha), and high densities (> 5 x 104/ha) in 13-yr stands, and 110-yr mature stands). We developed allometric equations for predicting belowground biomass by destructive harvesting, used existing site-specific allometric equations for aboveground biomass, and directly measured C stocks in litter, fine roots, and soils. Aboveground net primary productivity (ANPP) was estimated as the change in aboveground biomass plus annual litterfall, and total belowground carbon allocation (TBCA) using a C balance approach (TBCA = soil CO2 efflux minus C inputs from aboveground litterfall plus changes in C stored in litter, soil and coarse roots). The proportion of biomass found belowground increased with increasing stand density in young stands, but this increase was mostly related to differences in allocation patterns associated with tree size, and not increased competition for belowground resources. ANPP and TBCA increased with stand density in the 13-yr stands (ANPP was 64, 130, and 165 g C m-2 yr-1 and TBCA 86, 249, and 304 g C m-2 yr-1 for low, moderate and high density stands, respectively), and young stands had significantly lower values than the mature stands (ANPP was 275 and TBCA 389 g C m-2 yr-1 for 110-yr stands). The ratio of TBCA : TBCA + ANPP did not differ with density for the 13-yr stands or with age, remaining relatively constant at 0.57-0.65. Validating the different components of the carbon budget is important for defining allocation rules that allow accurate predictions of C storage and fluxes in forested ecosystems.
KEY WORDS: aboveground net primary productivity (ANPP), carbon allocation, lodgepole pine, total belowground carbon allocation (TBCA)