Height development of Betula and Salix species following precommercial thinning at various stump heights: 3-year results

Topping, to reduce competition, may be an attractive alternative to traditi onal precommercial thinning in forestry for both biological and financial r easons. In this study, the height development of secondary and main stems o f birch (Betula pubescens Ehrh. and Betula pendula Roth, species not separa ted), and secondary stems of willow (Salix spp.) was examined in a field ex periment in northern Sweden. Treatments studied were: traditional precommer cial thinning, topping at 40% of main stem mean height, topping at 70% of m ain stem mean height, and controls (untreated). Post-treatment damage to th e trees was frequent for both genera, but especially for the willows. Treat ment rankings for all of the secondary stems, and for undamaged secondary s tems, according to height development after three growing seasons, were top ping at 70% greater than or equal to no treatment greater than or equal to topping at 40% greater than or equal to traditional precommercial thinning. The results also indicated that the cross-cutting level could be raised to a level of at least 40% of main stem height, without risking the main stem s becoming overtopped. During the study period, 67% of the main stems excha nged their leading shoots at least once.