Indices of branch contribution to bole growth in Pinus resinosa Ait.

Abstract

The contribution of individual branches to the current annual xylem increment of the main stem of six young red pine (Pinus resinosa Ait.) was investigated. Logical estimates of branch productivity including: branch foliage dry weight, current extension length of the primary branch axis, and the current annual xylem increment measured as ring width at branch base (CAXI-branch base); were related to wood growth on the tree bole. CAXI-branch base was hypothesized to be the best single indicator of a branch's contribution to bolewood growth. This parameter was incorporated into a crown vigor index (CVI) designed to simulate vertically distributed bolewood increment. CVI was also related to other similar bole growth simulation models. No clear correspondence was found between the vertical distribution of the annual bolewood increment and the branch parameters: foliage dry weight, current extension length of the primary branch axis, and CAXI-branch base. The regularity of these branch parameter measurements throughout the tree crown compared to a well defined bolewood increment pattern suggested, however, that an indirect relationship between the two existed. The incorporation of CAXI-branch base into the crown vigor index made it possible to statistically relate this branch parameter to actual bolewood increment. CVI bole growth simulations, in general, corresponded closely to bolewood increment values. Notable exceptions occured on trees with anomalous growth patterns and at points of localized bending stress. CVI bole growth simulations proved to be superior to other bole growth models of similar construction. The technique for measuring CAXI-branch base is a destructive process which is complex and tedious. A practical modification to the CVI model was to estimate CAXI-branch base from readily obtainable branch parameters. The best estimate of CAXI-branch base was the product total branch foliage dry weight and the current extension length of the primary branch axis.