Population dynamics in a 6-year-old coppice culture of poplar: II. Size variability and one-sided competition of shoots and stools

Abstract

Coppice cultures are characterised by a high stool and shoot density. Studies on density-dependent mortality, and intraspecific competition in crowded populations have mainly focused on non-woody species. We investigated intraspecific competition in a coppice culture of poplar ( Populus spp.). A high-density plantation with 17 poplar clones was established in April 1996, coppiced (i.e. cut back) in December 1996 and subsequently grown for 4 years (1997–2000). High stool mortality was observed in the establishment year. Frequency distributions of stool and shoot size, and the relationship between shoot biomass and shoot density was determined for the different clones during the 4-year rotation. Stool mortality was not correlated with stool density. In the paper it will be argued that stool competition was probably very low, although increasing by the end of the rotation. Stool mortality was caused by Melampsora rust infections, implicating that process based yield models for poplar SRC should take into account rust infections. Skewness and inequality of shoot size distributions were very high at the start of the rotation, but progressively decreased during the course of the experiment. No self-thinning line was found, although high shoot mortality was evident for all clones. Therefore, it might be argued that shoot elimination within a stool was not due to light competition, but to another physiological mechanism within the stool/dominant shoot.