Genetic variation and productivity of Populustrichocarpa and its hybrids. VIII. Leaf and crown morphology of native P. trichocarpa clones from four river valleys in Washington

Abstract

A common-garden study of Populustrichocarpa Torr. & Gray was initiated in 1985, when clonal material from 128 trees was collected from sites distributed along two mesic (Hoh, Nisqually) and two xeric (Dungeness, Yakima) river valleys. This material was grown for 1 year at Puyallup, Wash. In spring 1986, cuttings from this material were used to establish two replicate plantations, one at Puyallup and the other at Wenatchee, Wash. Data were collected from a subset of 80 clones on 8 single-leaf and 14 crown traits after two growing seasons. Analyses of variance revealed significant (p ≤ 0.10) differences among rivers in nearly all single-leaf traits by the second year at both plantations. Two-year leaf sizes at Puyallup significantly declined in this order: Hoh (388 cm2) > Nisqually > Dungeness > Yakima (194 cm2). At Wenatchee, a similar mesic > xeric pattern was found among river sources, but leaves were smaller there. When grown at Puyallup, leaves of clones from lower elevations in the Yakima valley were significantly (p ≤ 0.10) smaller, lighter, thinner, and weighed less per unit area than upper elevation clones. Chi-square tests showed that abaxial leaf surfaces were greener in Yakima trees than in trees from other locations, especially in those from the the lower Yakima valley. In the crown traits of trees grown in Puyallup, river and clone-within-site-within-river effects were significant for all traits, whereas site-within-river effects were significant for only 8 traits. Mesic-origin trees were significantly larger in size traits, e.g., branch length, than xeric-origin trees. Trees from the Yakima drainage system were leafier and branchier (p ≤ 0.10) than both Nisqually and Hoh trees. Values for most crown traits were greater (p ≤ 0.10) in the xeric, lower Yakima clones than in the mesic, upper Yakima clones. These mesic-xeric differences were similar for Dungeness trees, although there were few significant differences between the lower and upper elevational groups. Single-leaf and crown traits of trees from the four river valleys seem to be adapted to the respective mesic and xeric conditions of the source environments. Within the Yakima river valley, a sharp change in leaf and crown traits and in atmospheric moisture levels coincide midway along the transect, suggesting the presence of a steep selection gradient in the Bristol Canyon area.