The effects of thinning on the structural diversity of coppice forests

Abstract

Coppices are currently at a turning point: traditional uses have been abandoned and silviculture must be redefined according to new uses. Thinning to improve the development of trees is often the silvicultural treatment chosen. This paper attempts to assess the changes in forest structural diversity induced by different thinning regimes applied in coppice stands of Quercus pyrenaica and Quercus faginea. Structural diversity is analysed through spatial pattern, crown dimensions, vertical and horizontal differentiation and foliage height diversity. Moderate and heavy thinning have similar effects on stand structure, but the effects of light thinning are quite different for both species. The spatial pattern shows a greater regularity as the intensity of the thinning regime increases. The response of Q. pyrenaica to thinning is noticeable both in tree height and crown diameter, whilst in the case of Q. faginea, trees reacted to thinning by developing epicormic sprouts on the stem from the base of the crown. Vertical differentiation shows opposite trends in both species: increasing the intensity of thinning leads to an increase in vertical differentiation with Q. pyrenaica, but to a greater homogenisation shortly after thinning with Q. faginea. A neighbourhood analysis using Gadow's differentiation index is able to provide useful information on the changes in microstructure, while foliage height diversity index can be used to describe complex changes in the vertical structure of the stand. © INRA, EDP Sciences, 2005.