A study of morphological variation in Pseudotsuga menziesii in southwestern British Columbia

Abstract

Variation in needle and twig anatomy for 46 populations of Pseudotsuga menziesii was apportioned into that due to (i) taxonomic structure (the variety menziesii from coastal areas, the variety glauca from east of the Cascade crest, and intermediates from intervening areas); (ii) populations; and (iii) individual trees within populations. The variation was classified on the basis of summary variables, the principal components resulting from principal components analysis. Principal components analysis was performed both on original needle and twig variables and on residuals from multiple regression analysis of elevation, latitude, and longitude. The analysis of residuals removes the effect of allopatry and macroclimate. In both analyses, the smallest source of variation was taxonomic structure while most of the variation occurred within populations, suggesting that recognition of subspecific taxa in this portion of the geographic range is not appropriate. The results of analyses of original variables and residuals were highly correlated, indicating that relationships between individuals are not the result of allopatry or selection due to macroclimate. The observation that individuals account for most of the variation in the data is interpreted as indicating that the production of individual variants is a more significant evolutionary event than population differentiation.