COMPETITIVE EFFECTS OF CONSPECIFIC AND HERBACEOUS (WEEDS) PLANTS ON GROWTH AND BRANCH ARCHITECTURE OF POPULUS-XEURAMERICANA CV EUGENEI

The influence of tree density (2 x 3, 1 x 2, and 0.5 x 1 m) and weed c ontrol (weedy vs. weed free) on the growth and branching architecture of Populus Xeuramericana cv. Eugenei was examined in an experimental p lantation in southwestern Michigan, U.S.A. In the presence of weeds, p oplars were shorter (p < 0.0001), had a smaller basal diameter (p < 0. 0001), initiated fewer branches (p = 0.0004), and had fewer living bra nches (p = 0.002), shorter branches (p < 0.0001), and branches that sp read outward (p < 0.0001). Increasing tree density decreased poplar he ight (p < 0.0001), basal diameter (p < 0.0001), branch length (p = 0.0 062), and the number of living branches (p < 0.0001). At high densitie s, branches spread outward at their origin (p = 0.0015) and then curve d sharply upward (p = 0.002). At the highest planting density there wa s no difference in branching in plots with and without weed control. H owever, poplars in the weedy treatment were smaller than those in the weed-free treatment (p < 0.0001). Our results demonstrate that poplar growth and architecture can be influenced by competitors of very diffe rent stature. Weeds, in fact, have a greater effect on growth than con specifics. As a result, poplars grown in the presence of weeds are stu nted relative to poplars grown in the absence of weeds, even at the hi ghest tree density where the competitive effects of poplars reduced we ed biomass.