INFLUENCE OF SPACING AND SHORT ROTATIONS ON POPULUS-TRICHOCARPA X DELTOIDES COPPICE

Height growth and dry woody biomass production were studied on Populus trichocarpa x deltoides (Beaupre) coppiced at 1-, 2-, and 3-year intervals on a converted woodland in central France. For each rotation, two different planting densities were studied, ranging from 2000 to 20 000 cuttings per hectare. The experiment, which lasted for 6 years, allowed comparisons between establishment and subsequent coppice cycles on relatively large treatment plots (400 stools per plot). The highest planting densities yielded fewer shoots per stool and reduced height and diameter growth. Individual stool biomass was reduced by high stool densities; however, total biomass per unit area was higher, resulting from the greater number of stools. Height growth was greatly influenced by climatic variability, principally rainfall. Biomass production was greater after coppicing than during the establishment phase for the 2- and 3-year rotations, in spite of low water availability. Biomass production decreased in the 1-year rotation during 3 years, but was subsequently followed by a higher production, in strong relation with water availability. At the planting density of 5000 per hectare, total biomass yield was higher for the longest rotations. There was no evidence of ageing of the stumps even after six 1-year rotations.