IMPACT OF HERBACEOUS COMPETITION AND DRAINAGE CONDITIONS ON THE EARLY PRODUCTIVITY OF WILLOWS UNDER SHORT-ROTATION INTENSIVE CULTURE

The productivity of trees under short-rotation intensive culture is influenced by herbaceous competition and drainage conditions. During the first year of establishment of Salix discolor Muhl. and Salix viminalis L., four weed-suppression treatments were applied to two sites showing different drainage conditions, one well drained and the other is poorly drained. On the well-drained site, the productivity of the trees increased in all the plots under treatment, whereas on the poorly drained site, only the use of a plastic mulch increased the biomass production. The mean productivity on the well-drained site was always superior to the productivity measured on the poorly drained site except when the vegetation was controlled by the use of a plastic mulch. The analyses related to nutrition revealed that the trees on the well-drained site absorbed more nutrients than those on the poorly drained site. Salix discolor showed a higher uptake of potassium and S. viminalis, a higher concentration of calcium. Our results indicate that weed suppression is essential to the establishment of trees in short-rotation intensive culture and that the use of a plastic mulch proved to be particularly profitable on marginal sites.