DO EDGE EFFECTS INFLUENCE TREE GROWTH-RATES IN DOUGLAS-FIR PLANTATIONS

Patch size and edge structure are known to influence microclimate, for est dynamics, and other ecological properties wtihin forest fragments. Little is known about the nature of such ''edge effects'' within youn g plantations embedded in a matrix of older forest. Here we test the h ypothesis that the growth rates of young Douglas-fir trees are reduced near the edges of plantations due to shading effects from adjacent fo rests. This hypothesis was examined in a single plantation where light levels were thought to be substantially reduced on the southern edge due to shading from a neighboring stand. Density of all trees and the heights and diameters at breast height (dbh) of artificially-regenerat ed Douglas-fir trees were measured along three parallel transects that extended 120 m into the plantation from its southern edge. We found t hat both tree height and dbh were significantly related to distance fr om the plantation edge when the effects of tree density were controlle d for. Tree size was lower at 20 m from the edge than at all distances further from the plantation edge. These results suggest that the hypo thesis merits additional testing with a replicated design across a ran ge of environmental settings. The negative edge effect of tree growth reported here has implications for the design of plantation size, espe cially where small ''gap'' cuts are used.