Tree growth and stand development in short-rotation Populus plantings: 7-year results for two clones at three spacings

Two Populus hybrids (11-11 and D-01) were planted in monoclonal block plantings at three spacings (0.5, 1.0, and 2.0 m) near Olympia, Washington, and evaluated over a 7-year period for individual tree growth rates and above-ground stand productivity. Differences were substantial between clones and among spacings in both individual tree characteristics (height and diameter growth) and stand productivity (leaf area, basal area, or biomass production). Relative differences in growth between the clones tended to increase with spacing. Woody biomass production of clone 11-11 averaged 18.2 Mg ha−1 yr−1 at the 1.0 m spacing, whereas clone D-01 averaged only 10.1 Mg ha−1 yr−1 at that spacing. The clones differed in phenology of height and diameter growth, maximum rate of periodic height growth, tendency to produce sylleptic branches, partitioning of woody biomass, and sensitivity of growth rates to competition. All of these characteristics have important influences on the productivity of short-rotation plantations.