Lance W. Kress

An Investigation of the Impacts of Elevated Carbon Dioxide, Irrigation, and Fertilization on the Physiology and Growth of Loblolly Pine

Southern pine forests that are dominated by loblolly pine (Pinus taeda L.) are the most intensively managed forests in the United States. They provide more than 50% of the total softwood being harvested annually in the United States and represent the first or second most economically important agricultural crops in nine of the twelve southeastern states (U.S. Department Agriculture Forest Service, 1988). Thus, any changes in environmental conditions that will alter productivity of these forests will have important ecological, economical, and sociological consequences. Over the past several decades, the environment of southeastern forests has been changing. Increases in acidic deposition (SO4 and NOx), nitrogen inputs (Husar, 1986), atmospheric CO2 concentration (Conway et al., 1988; Keeling et al., 1989), and tropospheric ozone have all been documented to parallel the increase in population since the beginning of the industrial revolution. Climate change has also been predicted for the southeastern United States for the future. Each of these atmospheric and climatic elements that are being altered by human activities has the potential to affect productivity of southern pine forests. Nutrient availability, water availability, atmospheric CO2 concentration, and temperature are presently the principal factors that are limiting the productivity of southern pine forests. Thus, it is extremely important that we understand how changes in these factors will interact to affect physiological processes of forest stands.

Biomass-D2H relationships for young loblolly pine as affected by ozone

Abstract The influence of below and above ambient levels of ozone on the relationships between biomass components (foliage, branch, and stem) and DZH was examined using data from 1284 young loblolly pine ( Pinus taeda L. ) harvested from two ozone field studies. A In-in model form provided a very good fit of the biomass data. Residual plots showed no bias and R 2 ranged from 0.94 to 0.99. Ozone treatment significantly affected the shape of biomass— D 2 H relationships for all components except stem. For a given D 2 H , increasing ozone dose resulted in less foliage and more branch biomass. After adjusting for age and tree size, increasing ozone dose significantly increased number of branches after one year of ozone treatment. After the second year, ozone dose did not significantly change the number of branches when adjusting for tree size; however, the trends were the same as the first year. Because of the strong negative ozone effect on foliage biomass, total biomass for a given D 2 H was less for increasing ozone dose. Ozone effects need to be considered when developing biomass equations for young loblolly pine trees.