A Procedure for Calculating Daily Moisture Stress and Its Utility in Regressions of Tree Growth on Weather

Abstract

A method is described for computing daily values of moisture stress on forest vegetation, or water deficits, based on the differences between Thornthwaite's potential evapo—transpiration and computed soil—moisture depletion. More realistic functions are used for soil—moisture depletion on specific soil types than have been customary. These functions related daily rates of depletion to characteristics of soil—moisture tension. Separate functions account for surface soil wetting and drying processes following rain and during dry periods. Two methods of summarizing the day—to—day distribution of moisture stress are illustrated. One utilizes directly accumulated stress values during such logical growth intervals as periods of leaf flushing or bud setting. In an example of a regression of red pine shoot growth on water deficits, 72% of the variation in annual growth was accounted for by moisture stress during certain periods of both previous and current growing seasons. The second method computes moisture stress and weather variables as functions of time over two growing seasons and utilizes the coefficients of orthogonal polynomials as independent variables in regressions of growth. In an example of western white pine basal area growth utilizing this latter method, moisture stress accounted for a 28% reduction in the variance of growth remaining after the effects of temperature and precipitation per se had been removed. The complete model accounted for 78% of the total variation.

Climate and annual ring growth of black spruce in some Alberta peatlands

“…In upland forests, the previous year's rainfall was also as important to tree-ring growth as current year rainfall (Tryon and True 1958;Zahner and Stage 1966). The needles of black spruce, for example, are formed in the bud the previous year and remain on the trees for several years.…”

Differing growth responses to climatic variations and soil water deficits of Fagus sylvatica, Quercus petraea and Pinus sylvestris in a temperate forest

“…They highlight the growth sensitivity of each species to monthly temperatures and precipitation. Additional physiological 0378 indices, such as related to soil water deficits (Zahner and Stage, 1966), are used rather than climatic data to allow biological interpretations of the growth response to climate. These indices could be better correlated with radial growth than monthly climatic variables (Foster and Leblanc, 1993) because soil water availability is a major limiting factor for tree growth.…”

Climate-tree-growth relationships of European beech (Fagus sylvatica L.) in the French Permanent Plot Network (RENECOFOR)

“…Different studies have used daily climatic parameters to define "physiological" indices such as potential evapotranspiration, soil-moisture stress. (Zahner and Stage 1966;Zahner and Donnelly 1967;Giles et al 1985;Wickramasinghe 1988;Roberston et al 1990). In their physiological approach to dendroclimatic modeling of oak radial growth, Foster and LeBlanc (1993) clearly showed that individual physiological response indices were better correlated with radial growth than were monthly climatic variables, and were more amenable to biological interpretation than models using monthly climate variables.…”