Geographic Variation of Vegetative Characters of Populus deltoides

Abstract

Spatial autocorrelation was used to study the patterns of geographic variation in Populus deltoides (Salicaceae). Ten characters reflecting the vegetative morphology in this species were analyzed for each of 522 individuals in 302 localities scattered throughout eastern North America. Factor analysis reduced the dimensionality of the matrix. The first factor, reflecting leaf size, shows a clear clinal pattern throughout the study area, with larger leaves in the south and southeast. Other factors, reflecting twig size, leaf apical shape, and leaf base shape also exhibit spatial patterns but on a smaller geographic scale. The influence of large-scale environmental and climatice variation on these patterns was examined by regressing the factor scores against a matrix of five environmental parameters. The regression residuals were then examined for spatial pattern. In most cases the residuals retain no spatial patterning. However, the first factor, that reflecting leaf size, shows some small-scale pattern.