Contrasting Patterns of Carbon Flux and Storage in Pine Forest Ecosystems of the Atlantic Coastal Plain: Implications for Ecosystem Restoration and Climate Change Mitigation.

Abstract:

Forest ecosystems in the Southeastern US have high rates of productivity but are underutilized as a medium for the mitigation of atmospheric CO₂. In the lower Atlantic coastal plain, three pine species (longleaf [Pinus palustris], loblolly [P. taeda] and pond [P. serotina]) are the dominant overstory trees in a variety of wetland and upland ecosystems. These forest types can exist in close proximity throughout coastal plain landscapes, but exhibit contrasting patterns of productivity, pyrogenic C emissions, and mortality, thereby creating contrasting patterns of C assimilation and long-term C storage. Here, we combine field-based estimates of forest C storage and pyrogenic C emissions with LiDAR-based estimates of forest canopy heights in three contrasting forest ecosystems to 1) model their respective patterns of forest growth, mortality, and decomposition, 2) estimate the contribution of pyrogenic C fluxes to the ecosystem C budget, 3) estimate their potential upper bounds of forest C storage, and 4) model the impacts of current forest management practices and disturbance regimes on long-term forest C storage. Our results suggest that even though longleaf pine forests store comparatively little C in soil or belowground biomass, these forests nevertheless have the highest capacity for long-term C storage, in part due to their longevity. By contrast, while pond pine ecosystems have the highest capacity for long-term belowground C storage, they also have the lowest capacity for long-term aboveground C storage, one that is rarely achieved due to infrequent, high-severity disturbance regimes. Loblolly pine forests, while capable of higher growth rates than either longleaf or pond pine when in early stages of succesion, lack the long-term C storage capabilities of longleaf pine due to earlier senescence. Pyrogenic C emissions in these ecosystems are dominated by the combustion of ground and duff materials and occur over timescales ranging from rapid combustion in fire-maintained longleaf pine forests to smoldering events that can last for weeks in pond pine Pocosins. However, timber harvesting remains the dominant driver of C storage throughout the landscape, with very few forests realizing their full potential for long-term C storage.