Genetic variation in cold hardiness of Douglas-fir in relation to parent tree environment

Abstract

The extent to which parent trees within breeding zones of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) are locally adapted to their native environments was evaluated. Forty families from each of one Coastal and one Cascade breeding population in Oregon were assessed for cold hardiness and growth phenology, and family means for traits were summarized using principal components analysis (PCA). Composition of the first two principal components (PCs) was consistent between breeding zones, years, and test sites. PC-1, describing 39-46% of trait variation, represents a suite of traits related to spring phenology and spring cold hardiness. PC-2, describing 20-22% of trait variation, consists of cold-hardiness traits not associated with phenology. The first two PCs from each population, as well as univariate traits, were regressed on parent tree location variables and modeled climatic indices separately. In the Coastal zone, PC-1 was weakly but significantly related to temperature and moisture regimes (0.176 [Formula: see text] r2 [Formula: see text] 0.235), varying with elevation and distance from the ocean. PC-2 was related to temperature and moisture regimes in both populations (0.087 [Formula: see text] r2 [Formula: see text] 0.249). These relatively weak geographic patterns for adaptive traits within breeding zones suggest that current zone size is not excessive and could likely be increased north or south.