Cone Production of Douglas-fir and Grand Fir and its Climatic Requirements

Abstract

Thirty-six-year records of Douglas-fir and grand fir cone counts were analyzed with eight climatic variables to find which combinations of climatic factors were related to the induction of reproductive buds and the successful development of the strobili. Cool, cloudy weather during June, July, and August, 26–24 months before cone maturation, was the first prerequisite for abundant reproductive bud initiation. The second was cold, sunny weather during December, January, and February, 20–18 months before cone maturation. A wet April, 16 months before cone maturation, resulted in a higher proportion of megasporangiate strobili being differentiated, while a warm, dry, sunny June, 14 months before cone maturation, favored successful bud development. Since the prerequisites for a good cone crop include an alternation of cool, moist summers (2 years prior) and warm, dry summers (1 year prior), good cone crops in two consecutive years can not be expected. And since additional environmental prerequisites must be fulfilled, a lapse of several years between good cone crops is probable.