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Invasive insects can impact ecosystem functioning by altering carbon, nutrient, and hydrologic cycles. In this study, we used eddy covariance to measure net CO 2 exchange with the atmosphere (NEE), and biometric measurements to characterize net ecosystem productivity (NEP) in oak-and pine-dominated forests that were defoliated by Gypsy moth (Lymantria dispar L.) in the New Jersey Pine Barrens. Three years of data were used to compare C dynamics; 2005 with minimal defoliation, 2006 with partial defoliation of the canopy and understory in a mixed stand, and 2007 with complete defoliation of an oak-dominated stand, and partial defoliation of the mixed and pine-dominated stands. Previous to defoliation in 2005, annual net CO 2 exchange (NEE yr ) was estimated at À187, À137 and À204 g C m À2 yr À1 at the oak-, mixed-, and pine-dominated stands, respectively. at the oak-, mixed-, and pine-dominated stands, respectively. At the landscape scale, Gypsy moths defoliated 20.2% of upland forests in 2007. We calculated that defoliation in these upland forests reduced NEE yr by 41%, with a 55% reduction in the heavily impacted oakdominated stands. 'Transient' disturbances such as insect defoliation, nonstand replacing wildfires, and prescribed burns are major factors controlling NEE across this landscape, and when integrated over time, may explain much of the patterning of aboveground biomass and forest floor mass in these upland forests.

We developed a volume-to-biomass method based on age groups representative of forest development stages to estimate live tree biomass, C, and biomass and C accumulation rates of China's forests between 1973 and 1993. The data were from plot-level forest inventory, national-level inventory statistics, and ecological site studies specified to estimate biomass in different tree components. Our results indicate that carbon storage in China's forests was 4.34 Pg C in the early 1990s, an increase of 13% since the early 1970s. The annual forest C sequestration rate from the late 1980s to early 1990s was 0.068 Pg C/yr and approximately four-to five-times higher than in the 1970s and 1980s. The large C sink in China's forests in the early 1990s was likely related to age structure changes that had developed to more productive stages, a consequence of reforestation and afforestation programs from the 1960s. The results were compared with other C store estimates, which were based on the same inventory data. Various methods can produce estimates that differ in the direction of C flux as well as its magnitude. Separating age groups with the volume-biomass method could cause a 27% difference in estimated carbon pools but an 89% difference in C sequestration rates whereas the biomass density method would provide an estimate that differs by 65% in the C pools.

This paper reports results of a study designed to examine the control that soil temperature exerts on soil processes associated with nutrient flux, and in turn, on tree nutrition in interior Alaska black spruce ecosystems. Approximately 50 m2 of forest floor in a 140-year-old black spruce ecosystem, which had developed on permafrost, was heated to 8–10 °C above ambient temperature. This perturbation amounted to approximately a 1589 degree-day seasonal heat sum (above 0 °C), 1026 degree-days above the control total of 563 degree-days. The forest floor, surface 5 cm of mineral soil, and soil solution were compared with those of an adjacent control plot to evaluate the change in nutrient content and decomposition rate of the forest floor. The nutritional response to soil heating of current black spruce foliage also was evaluated. Soil heating significantly increased decomposition of the forest floor, principally because of an increase in biomass loss of the O21 layer. The increased decomposition resulted in greater extractable N and P concentrations in the forest floor, higher N concentrations in the soil solution, and elevated spruce needle N, P, and K concentrations for the experimental period. These results are discussed in light of the importance of soil temperature and other state factors that mediate ecosystem function.

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