Early Growth Patterns of Red Alder and Black Cottonwood in Mixed Species Plantations

Abstract Growth patterns of black cottonwood ( Populus trichocarpa Torr.& Gray) cuttings and red alder (Alnus rubra Bong.) wildlings were studied during the first year after planting on low elevation glacial till soils in western Washington, U.S.A. Black cottonwood height growth occurred earlier, with 88 percent of its height having been achieved by late July (Julian day 210). Red alder growth continued longer, with 55 percent of its height growth achieved after late July (Julian day 210). Black cottonwood of this genetic origin appeared to have a more preformed growth pattern than red alder. Leaf area ratios were consistently higher throughout the season for black cottonwood than for red alder-a maximum of 42 cm²/g for black cottonwood and 29 cm²/g for red alder. Growth parameters in both species were adversely affected by periods of no precipitation and soil drought. Biomass production for the first year was low-0.04 metric tons/ha for black cottonwood and 0.74 metric tons/ha for red alder-compared to other studies in the region where black cottonwood and red alder were planted to closer spacings. The general ability of black cottonwood to achieve its growth earlier in the season coupled with greater leaf area ratio may explain its different behavior from red alder in mixed stands. Forest Sci. 31:190-200.