Size of Douglas-fir trees in relation to distance from a mixed red alder–Douglas-fir stand

Abstract

Variation in diameter, height, and stem volume of 57-year-old Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco) 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 (Alnusrubra Bong.). Within the interplanted strip and despite its greater total stand density, bole volume of dominant and codominant Douglas-fir averaged 1.27 m³ compared with 0.55, 0.45, 0.46, or 0.49 m³ 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 about 15 m beyond the edge of the mixed stand at this poor quality site in southwest Washington. We infer that similar ribbonlike distributions of naturally regenerated red alder could be retained to improve growth of nearby conifers on nitrogen-deficient sites.