Unusual drought symptoms in Douglas fir

Abstract

Defoliation of the mid crown of Douglas-fir trees on Vancouver Island followed the hot, dry summer of 1967. Reddening of foliage in a similar mid crown position occurred on other trees in the spring of 1968. The position of these effects could not be attributed to localized fungus infections, insects, or microclimatic influences. A differential response to moisture stress by affected tissues is thought to have caused the unusual patterns. Other effects are also described.