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CARBON STORAGE AND FLUXES IN PONDEROSA PINE AT DIFFERENT SUCCESSIONAL STAGES
Citation:
Law, B. E., J. Irvine, S. VanTuyl, P. M. Anthoni, P. Thornton, AND C P. Andersen. CARBON STORAGE AND FLUXES IN PONDEROSA PINE AT DIFFERENT SUCCESSIONAL STAGES. Presented at Ecological Society of America, Snowbird, UT, August 6-10, 2000.
Description:
We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, and eddy flux estimates of net ecosystem exchange. The young site (Y site) was previously an old-growth ponderosa pine forest that had been clearcut 15 years ago, and natural regeneration took place. The old-growth forest (O site) consists of two primary age classes (45 and 250 years), and in contrast, it has never been logged. Because of the logging activities at the Y site, the amount of fine- and coarse woody debris was 3 times that of the O site (2535 and 737 g C m-2 y-1). Annual soil surface CO2 flux, estimated from periodic chamber measurements, was similar at the Y and O sites (714 and 702 g C m-2 y-1). Annual ecosystem respiration (soil, foliage, live woody tissue, woody debris) was 911 and 908 g C m-2 y-1 at the Y and O sites, and soil fluxes accounted for 78 and 77% of Re. Aboveground net primary productivity (trees, shrubs, litterfall production) was lower at the Y site (177 versus 390 g C m-2 y-1 at the O site), and shrubs accounted for about 40% of the total. During the typical summer drought, eddy covariance measurements show that the old site was a stronger sink for CO2 than the young site. Leaf water potential and sapflow data suggest that water availability may have been more limiting to the shallow-rooted young trees. The lower ANPP and NEE at the young regenerating forest is likely the result of lower gross and net C uptake in the early successional stage (shallow root development limiting water use and C uptake, lack of canopy closure), and greater losses from decomposition relative to photosynthetic uptake. BIOME-BGC simulations of net ecosystem productivity will be used to evaluate controls on NEP at both sites.