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.