Growth dynamics and biomass production in short-rotation poplar plantations: 6-year results for three clones at four spacings

Growth dynamics and biomass production in short-rotation poplar plantations were evaluated at Hanyuan Forestry Farm, Baoying County, P.R.C. Experimental treatments applied in a split-plot design included: four planting densities (1111, 833, 625 and 500 stems ha−1); three poplar clones (NL-80351, I-69 and I-72) and three rotation lengths. Survival of all three clones was excellent at the experimental site under the imposed management regime. Differences in DBH, height, LAI and above-ground biomass production, however, were manifested among the treatments. Overall the clonal ranking was in the order NL-80351≥I-69>I-72 by age 6. LAI values ranged from 0.6 to 4.4 m2 m−2 and differences among four planting densities and three clones were significant throughout the first six years. Above-ground biomass productivity was affected considerably by planting density, clone and rotation length. Within the four densities, the highest biomass productivity at rotation age 6 was achieved in the highest stocked stand (1111 stems ha−1) for both clone I-69 and I-72, but in the stand of 833 stems ha−1 for clone NL-80351. A polynomial function was chosen to describe the relationship between LAI and current annual biomass increment; maximum biomass increments around 17 tonnes ha−1 a−1 were associated with LAIs of 4.0 m2 m−2. Based on the results over 6 years, we recommend that the best option for ground pulp timber production at a similar site is to choose clone NL-80351 and I-69 for planting materials, 6 years for rotation length and 833 or 1111 stems ha−1 for planting density.