Differences in Ecosystem Carbon Distribution and Nutrient Cycling Linked to Forest Tree Species Composition in a Mid-Successional Boreal Forest
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In the boreal forest of Alaska, increased fire severity associated with climate change is expanding deciduous forest cover in areas previously dominated by black spruce (Picea mariana). Needle-leaf conifer and broad-leaf deciduous species are commonly associated with differences in tree growth, carbon (C) and nutrient cycling, and C accumulation in soils. Although this suggests that changes in tree species composition in Alaska could impact C and nutrient pools and fluxes, few studies have measured these linkages. We quantified C, nitrogen, phosphorus, and base cation pools and fluxes in three stands of black spruce and Alaska paper birch (Betula neoalaskana) that established following a single fire event in 1958. Paper birch consistently displayed characteristics of more rapid C and nutrient cycling, including greater aboveground net primary productivity, higher live foliage and litter nutrient concentrations, and larger ammonium and nitrate pools in the soil organic layer (SOL). Ecosystem C stocks (aboveground + SOL + 0–10 cm mineral soil) were similar for the two species; however, in black spruce, 78% of measured C was found in soil pools, primarily in the SOL, whereas aboveground biomass dominated ecosystem C pools in birch forest. Radiocarbon analysis indicated that approximately one-quarter of the black spruce SOL C accumulated prior to the 1958 fire, whereas no pre-fire C was observed in birch soils. Our findings suggest that tree species exert a strong influence over C and nutrient cycling in boreal forest and forest compositional shifts may have long-term implications for ecosystem C and nutrient dynamics.
KeywordsBoreal forest wildfire soils aboveground net primary productivity Picea mariana Betula neoalaskana carbon nitrogen phosphorus base cations
We thank Camilo Mojica, Samantha Miller, Demetra Panos, Bethany Avera, Simon McClung, Alicia Sendrowski, Peter Ganzlin, Melanie Jean, and many additional undergraduate assistants at the University of Florida for help in the field and laboratory. Grace Crummer and Julia Reiskind provided analytical assistance, Heather Alexander generously shared unpublished tree C and N concentration data, and Rosvel Bracho provided guidance in setting up the incubation experiment and processing acquired data. We also thank Jamie Hollingsworth for logistical help. Funding for this research was provided by the Department of Defense’s Strategic Environmental Research and Development Program (SERDP) under project RC-2109. This study was also supported by the Bonanza Creek Long Term Ecological Research Program, which is jointly funded by the National Science Foundation and the U.S. Department of Agriculture Forest Service. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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