/ Understanding the vertical distributions of soil organic carbon (SOC) is key to predicting and simulating the influences of climate, global change, and human activities on the terrestrial carbon cycle. SOC was measured at soil depths of 0 -10, 0 -20, 0 -30, 0 -50, and 0 -100 cm in 2473 soil profiles during China's second national soil survey that was conducted from 1979 to 1992. SOC was spatially extrapolated for China. Mean SOC densities in the top 1 m ranged from 4.65 kg/m 2 for bare ground to 17.32 kg/m 2 in grassland land cover. SOC in the top 1 m of soil was estimated at 82.5 Ϯ 19.5 Pg C. The total SOC pool held in the top 10, 20, 30, 50, and 100 cm are 22%, 41%, 54%, 74%, and 100%, respectively. One of the objectives of the study is to examine the association of SOC content with climate and to estimate SOC storage in land-cover types at different soil depths. A partial correlation analysis shows that the mean annual precipitation was positively correlated with SOC content and the mean annual temperature was negatively correlated with SOC content, across all depths. The vertical distribution of SOC had a slightly stronger association with temperature than with precipitation in China.

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The 90,674 wildland fires that burned 2.9 million ha at an estimated suppression cost of $1.6 billion in the United States during the 2000 fire season demonstrated that forest fuel loading has become a hazard to life, property, and ecosystem health as a result of past fire exclusion policies and practices. The fire regime at any given location in these regions is a result of complex interactions between forest biomass, topography, ignitions, and weather. Forest structure and biomass are important aspects in determining current and future fire regimes. Efforts to quantify live and dead forest biomass at the local to regional scale has been hindered by the uncertainty surrounding the measurement and modeling of forest ecosystem processes and fluxes. The interaction of elevated CO 2 with climate, soil nutrients, and other forest management factors that affect forest growth and fuel loading will play a major role in determining future forest stand growth and the distribution of species across the southern United States. The use of satellite image analysis has been tested for timely and accurate measurement of spatially explicit land use change and is well suited for use in inventory and monitoring of forest carbon. The incorporation of Landsat Thematic Mapper data coupled with a physiologically based productivity model (PnET), soil water holding capacity, and historic and projected climatic data provides an opportunity to enhance field plot based forest inventory and monitoring methodologies. We use periodic forest inventory data from the USDA Forest Service's Forest Inventory and Analysis (FIA) project to obtain estimates of forest area and type to generate estimates of carbon storage for evergreen, deciduous, and mixed forest classes for use in an assessment of remotely sensed forest cover at the regional scale for the southern United States. The displays of net primary productivity (NPP) generated from the PnET model show areas of high and low forest carbon storage potential and their spatial relationship to other landscape features for the southern United States. At the regional scale, predicted annual NPP in 1992 ranged from 836 to 2181 g/m 2 /year for evergreen forests and 769-2634 g/m 2 /year for deciduous forests with a regional mean for all forest land of 1448 g/m 2 /year. Prediction of annual NPP in 2050 ranged from 913 to 2076 g/m 2 /year for evergreen forest types to 1214-2376 g/m 2 /year for deciduous forest types with a regional mean for all forest land of 1659 g/m 2 /year. The changes in forest productivity from 1992 to 2050 are shown to display potential areas of increased or decreased forest biomass. This methodology addresses the need for spatially quantifying forest carbon in the terrestrial biosphere to assess forest productivity and wildland fire fuels. #

Relative ozone sensitivity was evaluated among populations of Populustremuloides Michx. from each of five national parks differing in air quality. Eleven to 15 clones from each population were greenhouse grown and fumigated twice during 2 years of screening, each time with 180 ppb ozone for 6 h. The average injury for clones was significantly less for the most polluted park than for the least polluted park and there was a high negative association between average injury and ambient ozone levels. Differences in ozone sensitivity among clones within populations were highly significant and larger than differences among populations. These results suggest natural selection for tolerance in P. tremuloides may have occurred in some areas of eastern United States.