Document: STE-3-32-26

Leaf dynamics of longleaf pine (Pinus palustris) stands across an environmental gradient.

MCCONVILLE, D.J.*, M.P.SHEFFIELD, S.B.JACK and R.J.MITCHELL

Joseph W. Jones Ecological Research Center, Newton GA, USA ¹

Abstract:
It is wellestablished that weather affects leaf biomass dynamics by altering the timing and mass of both leaf accretion and senescence. The manner in which variation in weather influences these patterns across a landscape, however, is not well understood. This study was initiated to determine if foliage biomass dynamics are differentially affected across a soil water gradient (ranging from poorly to excessively drained) by annual and seasonal weather patterns in a mature longleaf pine forest. Between 1995 and 1999 monthly measurements of longleaf pine needlefall, soil volumetric water (TDR), precipitation, and air temperature were collected at extreme ends of the soil moisture gradient to estimate annual needle production, timing of seasonal senescence, and potential evapotranspiration (PET). To determine the timing of needle production, biweekly measurements of longleaf pine needle accretion were made from canopy access towers at two locations during the final year of sampling. Annual foliage production was significantly higher on the poorly drained sites: 197336 versus 61105 g/m² at the poorly and excessively drained sites, respectively. When analyzed proportionally, there were no significant differences in annual needle production between sites for the five year period. Moreover, neither the timing nor the rate of needle accretion was different between sites in 1999. Each site showed a bimodal pattern of needlefall with peaks in early summer and late fall. The proportion of early needlefall (May through August) was highly correlated with PET and significantly greater during relatively dry years for all sites. The early peak in needlefall was significantly higher at the excessively drained sites for all years suggesting that they are more affected by higher PET. As expected, the results suggest weather limits annual foliage production and influences timing of needlefall by causing early "drought induced" senescence during the summer when PET values are highest. However, observed differences in annual weather did not differentially affect foliage production between the extreme sitesboth the excessively and poorly drained sites were equally affected by weather in terms of annual leaf production.

Keywords: longleaf pine, weather, needle accretion, needlefall, potential evapotranspiration

This abstract is being presented at: 3:30 PM in session:
WATER RELATIONS