Examining different concepts for the development of a distance-dependent competition model for red pine diameter growth using long-term stand data differing in initial stand density

Abstract

Red pine (Pinus resinosa Ait.) data collected from age 13 to age 43 in a spacing trial were used to develop a distance-dependent individual-tree diameter growth model. The traditional concept of zone of influence in competition indices was redefined, and differences in asymmetry in above- and below-ground competition were represented. The availability of remeasured crown dimensions data allowed for realistic representation of the dynamics of crown interference at the canopy level. Diameter at breast height (dbh) increment was expressed in terms of absolute growth rate, relative growth rate, and ratio of absolute growth rate to crown width. The best relationships accounted for at least 80% of the variability in dbh increment. When tested on an independent data set, the model predicted dbh increment relatively accurately under different conditions of stand density. In particular, the change in dbh size distribution with the increase in competitive stress was well represented.