Genetic variation and productivity of Populustrichocarpa and its hybrids. I. Morphology and phenology of 50 native clones

Abstract

Morphological and phenological variation among 5 black cottonwood clones from each of 10 natural populations were studied at 1 plantation site in western Washington [USA]. Source populations are located in major river valleys, west of the Cascade Mountains, between central Oregon (latitude 44.degree. 44'' N) and southern British Columbia [Canada] (latitude 49.degree. 05'' N). Populations and individual clones were selected for superior form and growth rate. Tested at a spacing of 1.2 .times. 1.2 m, the 50 clones displayed a large range of variation in 15 leaf, branch and phenology characters studied. Clones and populations differed significantly in 14 and 10 characters, respectively. Population means for 7 characters and a character association (principal component) varied clinically with source latitude, longitude, and (or) elevation. The most consistent genetic cline follows a geographic gradient from southwest to northwest, southwestern clones develop smaller leaves on more numerous and more erect branches, and continue growth later in the fall. Variation patterns seem to reflect regional climatic gradients, annual disturbance in riparian environments and the life history characteristics of the species. The results point to the great potential of clonal selection for black cottonwood improvement.