The relative importance of initiation and early development on cone production in Douglas fir

Abstract

Lateral bud initiation as determined by increased succinic dehydrogenase activity in the axils of certain leaves occurs by April 1 in the Victoria area. The number of lateral buds initiated did not vary significantly in 1967 and 1968 while the number of buds which developed did. Not all primordia which are initiated develop. Some abort very early and disappear completely while others develop bud scales then cease development and become latent. The rest of the primordia fully develop as vegetative, male, or female buds. In 1967 when abundant cones developed, 56% of the primordia fully developed and most of these became reproductive buds. In 1968 when no cones developed, only 31% of the primordia fully developed and all of these became vegetative. The number of cones produced was, therefore, not determined directly by the number of primordia initiated but by the proportion of primordia which developed as reproductive buds. The presence of abundant maturing cones on shoots formed the previous year greatly reduces the number of primordia which develop and, also, reduces the possibility of these becoming reproductive buds. Previous vegetative growth and cone crops affect the cone productivity in subsequent years and help explain the cyclic pattern of reproduction in Douglas fir.