Wood production and structure in relation to bud activity in some softwood and hardwood species

The duration of cambial activity, and change in wood structure from early to latewood, are considered in relation to the initiation of scale and foliage leaves, and shoot extension, in Picea abies, Pseudotsuga menziesii, Quercus robur, Fraxinus excelsior, and Fagus sylvatica. The initiation of cambial activity appears to be associated with the production of the first scales at the shoot apex, but the cessation of cambial activity does not appear to coincide with the end of primordial initiation at the apex. In P. abies and P. menziesii leaf initiation continues at a rapid rate for several weeks after cambial activity has ceased. In Q. robur, F. excelsior, and F. sylvatica cambial activity continues longer than leaf initiation. The decline in vessel or tracheid diameter is not consistently related to the change from initiation of scales to initiation of foliage leaves. In the ring porous hardwoods the rapid decline in vessel diameter at the end of the earlywood coincides with the cessation of shoot elongation, but in the other species vessel or tracheid diameter declines steadily from the beginning of the earlywood.