Effects of Soil Water and Nitrogen Availability On Douglas-Fir Growth.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is the dominant forest plantation species in the Pacific Northwest.  One reason for the dominance of Douglas-fir is that it can grow in nearly all of the varied climates and soil types of the region.  Due to soil and climate differences, soil water and nitrogen availability differ considerably over the range of Douglas-fir.  An understanding of how these soil water and nitrogen differences might affect Douglas-fir growth is important to determine how wood quality might change throughout the region.  To determine climate and soil water availability, weather stations were installed in fifteen 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.  Six tree cores at each installation were sampled and measured to determine earlywood, latewood, and total growth each year.  This study will determine if site properties, environmental factors, and/or nutrition can effect radial growth of Douglas-fir.