Estimating Douglas-fir wood production from soil and climate data

Abstract

The relationships between annual tree-ring growth and growing season climate were explored, studying 70-year-old coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) trees in three sites of different moisture microclimates within productive forest lands. Climate data were augmented via a water balance model to calculate soil moisture deficits. Eleven ring variable components were derived via X-ray densitometry for each ring from two cores for each of 10 trees per site. First principal component scores of each ring variable were linked to climate variables (from 1951 to 1985) via multiple regression. Annual water deficit was found to account for 51% of the annual variations in ring weight. Earlywood width showed little direct climate response, and earlywood density was the least variable ring component. Latewood width was related to annual water deficit (r2 = 0.47). Latewood density showed different relationships to climate variables at the different sites. Percent latewood is increased by spring rainfall and depressed by high August temperatures. The ranges between minimum to maximum and earlywood to latewood densities were comparable for all sites, indicating that there is little density variation due to site differences.