Annual wood increment of slash pine (Pinus elliottii Engelm.) in relation to soil water deficits in East Texas

Abstract

The relationship of annual height, radial and volume increment to phenologically selected water deficits were tested and examined for consistency across a climatic gradient in East Texas. Increments were determined by stem analysis at five plantations and water deficits were computed using a modification of Thornthwaite's potential evapotranspiration method and daily weather variables. Scatter diagrams and correlation analyses showed that height increment was most strongly related to prior year water deficits while radial and volume increments were best related to current year water deficits. However, age was the dominant variable affecting annual increment for each growth parameter. Age alone accounted for 64 to 79 percent of the total variation in increment of individual parameters. The consistency of the increment water deficit relationship across a climatic gradient was tested using group regression analysis. Response of height, radial dbh and ring 2 increments to phenologically selected water deficits were significant and uniform, indicating consistency of relationship over the climatic gradient. The volume increment - water d e fic it relationship v/as significant but varied significantly among plots and with age among plots. Using the regression model developed for height it was shown that water deficits provided estimates of regional differences in productivity for otherwise homogenous sites.