Diurnal Variations in Stem Diameters of Small Trees

Abstract

Diurnal changes in diameters of small trees were determined in the greenhouse with an adaptation of the Fritts dendrograph. Separate experiments determined diurnal and seasonal variations in diameters when soil moisture was readily available, effects of recurrent droughts on diameter changes, and effects of transplanting on subsequent diameter changes. Extreme variability of diurnal expansion and contraction was found among trees. Seedlings that showed greatly different amounts of shrinking and swelling often were of the same general size and appearance. Reasons for variations in shrinkage among trees are discussed. As soil moisture was depleted during drying cycles, diurnal stem contraction predominated, with no expansion occurring at night. When shrinkage occurred, it was not localized and was detected throughout the main stem and branches. Transplanted trees shrank markedly even when soil moisture was maintained close to field capacity. In general, the ratio of cambial growth to stem shrinkage and expansion caused by hydration changes was too low to permit estimates of cambial growth of seedlings with the modification of the Fritts dendrograph.