The Effects of Site and Soil Characteristics On Pacific Northwest Douglas-Fir Growth.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is grown for commercial purposes throughout the Pacific Northwest (PNW), but its productivity differs over the diverse soils of the region.  Understanding Douglas-fir growth is very important for forest managers and researchers who want to predict growth and yield in the PNW.  The variation in age and makeup of soil parent materials in the PNW necessitates a better understanding of the effect of soil water and nitrogen availability Douglas-fir growth. Sixty Douglas-fir installations were installed from southern Vancouver Island, Canada to southern Oregon.  Previous growth of Douglas-fir was measured as King's site index, average annual basal area, and height to diameter at breast height ratio.  Current Douglas-fir growth was measured as the two-year percent change in basal area, height, and volume. To determine climate and soil water availability, weather stations were installed in Douglas-fir installations to measure precipitation, temperature, and soil moisture year-round.  PRISM data was also used to determine monthly precipitation and temperatures at each installation.  At the center of each installation, bulk density, soil texture, and total soil and forest floor carbon and nitrogen were sampled from a one-meter deep pit.  This study will determine if site properties, environmental factors, and/or nutrition can effect growth or biomass allocation in Douglas-fir.