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. Experiment al treatments applied in a split-plot design included: four planting densit ies (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. Dif ferences 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 greater than or equal to I-69 greater than or equal to I-72 by age 6. I,AI values ranged from 0.6 to 4.4 m(2) m(-2) and differences am ong four planting densities and three clones were significant throughout th e first six years. Above-ground biomass productivity was affected considera bly by planting density, clone and rotation length. Within the four densiti es, 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 bio mass increment; maximum biomass increments around 17 tonnes ha(-1) a(-1) we re associated with LAIs of 4.0 m(2) 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 densit y. (C) 1999 Elsevier Science Ltd. All rights reserved.