Tree-ring model interprets growth decline in natural stands of loblolly pine in the southeastern United States

Abstract

Annual ring widths and ring areas from 131 even-aged, natural, well-stocked stands of loblolly pine (Pinustaeda L.) in the Piedmont region were analyzed to reveal possible causes of a previously reported decline in radial growth. A linear aggregate model was used to separate independent factors that are known to contribute to radial growth variation in this species. Stand, site, and climatic conditions were reconstructed for each stand for the 36-year period 1949–1984 from previous inventories and from weather records at appropriately located stations. Within each of six 5-year age-classes, the model identified declines in both ring width and ring area associated with stand density, climate changes, and the passage of time. Regional climate first ameliorated this decline as pine stands passed from droughty conditions early in the 36-year period to a favorable climate during the middle of the period, and the decline accelerated later with the return of dry conditions toward the end of the period. The tree-ring model simulates a decline in radial increment in trees in natural pine stands between the ages of 20 and 45 years in the Piedmont which has averaged 1% per year since 1950. Part of the downward trend was attributed to increased competition, part to regional drought, and a considerable part to unidentified factors, possibly regional atmospheric deposition.

Radial growth trends of loblolly pine in the Virginia Coastal Plain

“…Reductions in radial growth during the 1970s and early 1980s for the Virginia 20/20 study are coincident in time with FIA estimates of radial growth reductions for the Virginia Coastal Plain (Fig. l), and with other loblolly pine growth declines reported in various parts of the southeast (Sheffield et al 1985;Zahner et al 1989;Ruark et al 1991;Bechtold et al 199 1;Van Deusen 1992~). Increased radial growth during the 1980s for loblolly pines (Figs.…”

“…Zahner (1963Zahner ( , 1968 found that earlywood growth is intrinsically uniform, while latewood growth is strongly regulated by the immediate, current moisture conditions. More recently, numerous studies have further quantified the effect of summer drought on decreased radial growth of loblolly pine (Cregg et al 1988;Friend and Hafley 1989;Zahner et al 1989;Jordan andLockaby 1990: Houle andDelwaide 1991) throughout most of its range.…”

“…Because these studies (Sheffield et al 1985;Zahner et al 1989;Ruark et al 1991;Bechtold et al I99 I ; Van Deusen I992a) are based on data collected in the early 1980s updating trends in radial growth are of interest from both a scientific and economic basis. Many foresters involved with forest health and productivity issues are curious as to whether growth rates have improved in the interim or continued to decline.…”

“…Updated trends in loblolly pine radial growth are particularly important given the data associated with identification of growth declines is in many cases over IO years old (Sheffield et al 1985;Zahner et al 1989;Ruark et al 199 I ; Bechtold et al 1991;Van Deusen 1992a). The USDA Forest Service first noted growth reductions in 1982 during analyses of forest inventory data from Georgia.…”

Predictions and Projections of Pine Productivity and Hydrology in Response to Climate Change Across the Southern United States

“…At present, it is uncertain if the southern forests will be able to maintain (or increase) present-day levels of productivity. For example, Zahner et al, (1988) recorded a decrease hi radial growth of loblolly pine (Finns taedd) during the years from 1949 to 1984 in Piedmont stands.…”