Clark, Kenneth (USDA-FS, PO. Box 232, New Lisbon, NJ, 08064; Phone: 609-894-0325; Email: firstname.lastname@example.org)
K.L. Clark *, J. Hom, N. Skowronski, T. Wyckoff, Y. Pan, M. Patterson, J. Dighton, D. Gray
As part of a collaborative effort between the Northern Global Change Program of the USDA Forest Service, National Fire Plan-funded research, and the LANDFIRE project, we studied how fire and fuels management affects carbon dioxide (CO2) sequestration by oak- and pine-dominated forests in the Pinelands of New Jersey. We used a network of fire weather and eddy covariance towers, extensive biometric measurements, and fuel load measurements pre- and post prescribed fire to quantify forest carbon dynamics. Despite the low nutrient status of sandy, coarse-grained soils in upland forests of the Pinelands, forest productivity was similar to other closed-canopy forests on the Atlantic coastal plain. Mean maximum net CO2> exchange during the daytime reached -20 to -25 umol CO2> m-2 s-1 during the growing season, and nighttime net CO2 exchange was a function of air and soil temperature, averaging 4 to 5 umol CO2 m-2 s-1 during the same period. Both day- and nighttime fluxes were constrained by drought, thus integrated CO2 exchange was nearly unaffected by soil moisture availability until drought stress became severe. Net CO2 exchange during the winter averaged 1.5 umol CO2 m-2 s-1during the day and less than 1 umol CO2> m-2s-1at night, corresponding with minimum LAI and low temperatures. Aboveground production estimated from biometric measurements indicated that ANPP was ca. 500 g m-2at all sites, and was dominated by fine litterfall production (ca. 75% of ANPP). The proportion of fine litterfall contributed by the understory increased from 7% to 43% from oak- to pine-dominated stands. Our flux tower and field-based estimates of forest productivity are consistent with FIA based estimates of NPP, but both satellite products (MODIS) and simulation models (PnET CN) overestimated forest productivity on this landscape, likely because of the difficulty in modeling soil moisture status accurately. When put in the context of annual net CO2 exchange, prescribed fire treatments released up to twice the amount of CO2 sequestered annually by these forests, equivalent to 1-3 years of fine litter production. Fire and fuels management may have longer term effects on carbon dynamics, because LAI does not recover to pre-fire levels immediately, and fires may have a “memory effect” on productivity of the understory. Our study contributes to an understanding of the environmental factors controlling forest productivity and fuel accumulation, and illustrates how fire and fuels management potentially affects carbon sequestration by forests in the Eastern US.