Abstract

In conventional forest management the fast-growing hardwoods such as birches (Betula pendula Roth and Betula pubescens Ehrh) were cleaned when they started to compete with the conifer plants. In general the natural regenerated birch plants of minimal energy value are removed when they are two-four meter high and start to suppress the undergrowth of Norway spruce plants. Today with an increasing interest of utilising biomass for fuel, mixed forest with a shade-tolerant main species and a fast-growing species combined could be an important supply and also an important ecological site for maintaining biodiversity. In an experiment which was established 1983 through 1985 eight localities in central and southern parts of Sweden (Lat. 58-61º N.) was used. The stands were 20-30 years old when the experiment was started and consisted of dense, even-aged, self-propagated birch. The birches sheltering young Norway spruces (Picea abies (L.) Karst.) either planted or self-propagated. All stands were growing on moist or mesic sites with high site indices. Among the thinning regimes two combinations should be reported here: 1) thinning of the birch overstory to create a shelter of 500 stems ha-1 (no-shelter) and 2) total removal of the birch overstory (shelter). The treatments were replicated on each locality. The shelter should be cut when the stand was 35-40 years old. When the experiments started the mean diameter of birches on all plots was 60 mm for birch (Betula pendula Roth and Betula pubescens Ehrh.) and 45-49 mm for Norway spruce. The amount of removed birch biomass at first treatment was 40.6 (range 13.7-64.5) tonnes dry weight (d.w.) ha-1 for shelter plots and 70.0 (range 34.9-142.7) d.w. tonnes ha-1 for no-shelter plots. In 1997 when all birches on shelter plots were cut, the amount of removed birch biomass was 45.3 (range 13.6-109.3) tonnes d.w. ha-1. Total amount of birch biomass during the period was 85.9 (range 40.9-145.3) tonnes d.w. ha-1 for shelter plots and 72.7 (range 34.9-142.7) tonnes d.w. ha-1 for no-shelter plots. The remaining Norway spruce stands have produced 32.9 (10.9-48.6) tonnes d.w. ha-1 growing under a birch shelter compared with 37.9 (5.0-63.4) tonnes d.w. ha-1 for pure spruce stands

Keywords

biofuel; mixed forest; pre-commercial thinning; Betula pendula; Betula pubescens; Picea abies

Published in

New Zealand Journal of Forestry Science
2000, Volume: 30, number: 1, pages: 16-28

SLU Authors

• Johansson, Tord

  • Department of Energy and Technology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Forest Science


Permanent link to this page (URI)

https://res.slu.se/id/publ/8680