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 traditional precommercial thinning in forestry for both biological and financial reasons. In this study, the height development of secondary and main stems of birch (Betula pubescens Ehrh. and Betula pendula Roth, species not separated), and secondary stems of willow (Salix spp.) was examined in a field experiment in northern Sweden. Treatments studied were: traditional precommercial thinning, topping at 40% of main stem mean height, topping at 70% of main stem mean height, and controls (untreated). Post-treatment damage to the trees was frequent for both genera, but especially for the willows. Treatment rankings for all of the secondary stems, and for undamaged secondary stems, according to height development after three growing seasons, were topping at 70% ≥ no treatment ≥ topping at 40% ≥ 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 stems becoming overtopped. During the study period, 67% of the main stems exchanged their leading shoots at least once.