Genetic variation and productivity of Populustrichocarpa and its hybrids.: IV. Performance in short-rotation coppice

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Abstract
Resprouting after harvest and rapid growth of sprouts are often considered essential for success of close-spaced, short-rotation cultural systems. This study examined resprouting, subsequent growth, and dry weight production following the initial 4-year harvest of a "common garden" trial of 50 clones of Populustrichocarpa Torr. & Gray. The clones were selected from 10 populations (sources) from major river drainages from western British Columbia, Washington, and Oregon. Additionally, three P. trichocarpa × P. deltoides (Bartr.) hybrids, a 'Robusta' clone, and a previously selected P. trichocarpa clone from Cottage Grove, Oregon, were included in the experiment. Mean yield of P. trichocarpa clones was 11.3 Mg•ha−1•year−1 (CV among clones = 61%) in the coppice rotation vs. 12.6 Mg•ha−1•year−1 (CV among clones = 40%) in the initial rotation; a difference that may, at least in part, be due to the use of less fertilizer in the coppice rotation. Nevertheless, a number of clones including the hybrids had higher yields in the coppice than in the initial rotation. Yield of clones in the coppice rotation was only moderately correlated with yield in the initial harvest (r2 = 0.48), but the same two clones, hybrids 11-11 and 11-05, were the top-producing clones in both rotations. Cumulative mortality of P. trichocarpa at the end of the experiment, including failed cuttings, averaged 36%, but was highly variable (range = 7–66% among clones). Yield in both harvests differed significantly among sources of P. trichocarpa. As with other components of productivity reported earlier, performance in coppice varied significantly among the 50 P. trichocarpa clones, and more so than in the first rotation. Populustrichocarpa clones identified as superior in coppicing in this experiment represent potential parents for new hybrids intended for short-rotation systems involving coppicing.