Stool mortality and development of a competitive hierachy in a Salix viminalis coppice system

Competition between individual plants in a dense willow coppice stand caused a high density-dependent mortality of stools. Negative growth and death occurred among the smallest stools, suggesting that self-thinning involves the death of individuals whose net assimilation rate falls below a specific threshold value. These observations are consistent with the asymmetric competition hypothesis. The average minimum stool weight in the beginning of the season, needed to gain weight during that season increased with stand development and was lowered by harvest, after which living stools that previously lost weight started to gain weight again. The relaxation of competitive pressure by harvest was only temporary and the competitive hierarchy which had become established during one cutting cycle became enhanced during the next cutting cycle. The observed high stool mortality is discussed in relation to differences between stool variation patterns which may occur in the stand.