GENETIC-VARIATION AND PRODUCTIVITY OF POPULUS-TRICHOCARPA AND ITS HYBRIDS .8. LEAF AND CROWN MORPHOLOGY OF NATIVE POPULUS-TRICHOCARPA CLONES FROM 4 RIVER VALLEYS IN WASHINGTON

A common-garden study of Populus trichocarpa Torr. & Gray was initiate d in 1985, when clonal material from 128 trees was collected from site s distributed along two mesic (Hoh, Nisqually) and two xeric (Dungenes s, Yakima) river valleys. This material was grown for 1 year at Puyall up, Wash. In spring 1986, cuttings from this material were used to est ablish two replicate plantations, one at Puyallup and the other at Wen atchee, Wash. Data were collected from a subset of 80 clones on 8 sing le-leaf and 14 crown traits after two growing seasons. Analyses of var iance revealed significant (p less than or equal to 0.10) differences among rivers in nearly all single-leaf traits by the second year at bo th plantations. Two-year leaf sizes at Puyallup significantly declined in this order: Hoh (388 cm(2)) > Nisqually > Dungeness > Yakima (194 cm(2)). 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 signi ficantly (p less than or equal to 0.10) smaller, lighter, thinner, and weighed less per unit area than upper elevation clones. Chi-square te sts showed that abaxial leaf surfaces were greener in Yakima trees tha n in trees from other locations, especially in those from the the lowe r Yakima valley. In the crown traits of trees grown in Puyallup, river and clone-within-site-within-river effects were significant for all t raits, whereas site-within-river effects were significant for only 8 t raits. Mesic-origin trees were significantly larger in size traits, e. g., branch length, than xeric-origin trees. Trees from the Yakima drai nage system were leafier and branchier (p less than or equal to 0.10) than both Nisqually and Hoh trees. Values for most crown traits were g reater (p less than or equal to 0.10) in the xeric, lower Yakima clone s than in the mesic, upper Yakima clones. These mesic-xeric difference s were similar for Dungeness trees, although there were few significan t differences between the lower and upper elevational groups. Single-l eaf and crown traits of trees from the four river valleys seem to be a dapted to the respective mesic and xeric conditions of the source envi ronments. Within the Yakima river valley, a sharp change in leaf and c rown traits and in atmospheric moisture levels coincide midway along t he transect, suggesting the presence of a steep selection gradient in the Bristol Canyon area.