Branch diameter and longevity linked to plantation spacing and rectangularity in young Douglas-fir

Abstract

The relation between branch growth characteristics and initial plantation spacing were observed in young Douglas-fir ( Pseudotsuga menziesii [Mirb.] Franco var. menziesii). Trees were sampled from Nelder plots ranging in initial density from 309 to 18,730 trees/ha and grown in either 1:2 or 1:1 rectangular spacing geometry. Data were derived using 3919 branches from 56 trees, 19 and 21 years old, at two sites in western Oregon. Branch diameters in the lower basal log and lower crown were measured outside bark, as well as number of years of radial and terminal growth of branches. Mean and maximum nodal branch diameter increased with decreasing initial tree density, as in previous studies. Within operational planting densities, 469 trees/ha (4.6 × 4.6 m) to 1682 trees/ha (2.4 × 2.4 m), mean branch diameter outside bark for the basal 5-m log ranged from 28 down to 16 mm and maximum branch diameter outside bark ranged from 36 down to 22 mm. Rectangularity of space had no effect on branch diameter. The number of nodal branches/m, living and dead, as well as years of radial and terminal branch growth increased with decreasing initial tree density, resulting in larger and more persistent branches. The number of years that lower branches remained alive without radial branch growth ranged from 0 to 8 years, but averaged about 1 year. Branch diameter was highly correlated with initial tree densities, allowing managers opportunities to improve wood quality through density management in young Douglas-fir plantations.