SIZE OF DOUGLAS-FIR TREES IN RELATION TO DISTANCE FROM A MIXED RED ALDER - DOUGLAS-FIR STAND

Variation in diameter, height, and stem volume of 57-year-old Douglas- fir (Pseudotsuga menziesii var, menziesii (Mirb.) France) was related to distance of these trees from a 27 m wide strip in the same Douglas- fir plantation that had been interplanted with red alder (Alnus rubra Bong.). Within the interplanted strip and despite its greater total st and density, bole volume of dominant and codominant Douglas-fir averag ed 1.27 m(3) compared with 0.55, 0.45, 0.46, or 0.49 m(3) in trees 15, 30, 45, or 60 m, respectively, from the edge of the mixed stand. Some positive influence of nitrogen-fixing red alder apparently extended a bout 15 m beyond the edge of the mixed stand at this poor quality site in southwest Washington. We infer that similar ribbonlike distributio ns of naturally regenerated red alder could be retained to improve gro wth of nearby conifers on nitrogen-deficient sites.