Distribution of Diurnal Fluctuations in Stem Circumference of Douglas-fir

Diurnal circumferential fluctuations were measured during late summer at different locations on the stems of several Douglas-fir trees.In one study, devices were installed to record periodically circumferential changes at five levels on the stems of study trees. The results indicated that the amplitude of diurnal fluctuation is considerably greater in a zone adjacent to midcrown than at levels above or below. Within this zone, shrinkage and subsequent dimensional recovery begin sooner and proceed at the greatest rates. The more dynamic fluctuation within this zone may relate to transpirational patterns in the crown and to factors determining "stem elasticity".In a related study, a tree was girdled. Results indicated that circumferential fluctuations are primarily seated in peripheral tissues removed in the process of girdling. Possible explanations and implications of the reported patterns are discussed.