Effects of environmental factors on estimated daily radial growth ofPinus resinosa andBetula papyrifera

Abstract

Relations between estimated daily radial growth of red pine (Pinus resinosa) and white birch (Betula papyrifera) trees and various environmental factors were studied in northern Wisconsin. Daily variations in stem radius, which reflected an irreversible cambial growth component as well as superimposed shrinkage and swelling of stems, were recorded with dendrographs and daily radial growth was estimated with trend lines connecting midpoints between daily maximum and minimum stem radii. Orthogonalized regression analysis was used to isolate individual effects despite intercorrelations between the variables. Regression models were developed on 9 independent variables: rainfall (log P, n), minimum temperature (Tmin, n; Tmin 2, n), average daily relative humidity (Ra, n), maximum saturation deficit with a one-day lag (Vmax, n−1), minimum temperature with a two-day lag (Tmin, n−2), percent soil moisture (log M150), time trend (Day2) and autocorrelation (y, n−1). These factors explained 81% of the variation in estimated daily radial growth of birch. They also explained 78% of the variation in growth of pine at the wettest site (lower slope) and 64% at the driest site (upper slope). As soil and plant water stress intensified up the slope, radial growth of pine was inhibited and the direct relation between growth and environmental factors was progressively weakened while the autocorrelation factor became dominant. Rainfall (log P, n) was the most important factor influencing radial growth, reflecting the paramount importance of cell turgor in the cambial zone.