The influence of a birch shelter (Betula spp) on the growth of young stands of Picea abies

In order to study the influence of a birch shelter (Betula pendula Roth and Betula pubescens Ehrh.) on yield and stand structure of Norway spruce (Picea abies (L.) Karst.), an experiment was established in eight localities in southern and central parts of Sweden. In the experiment two treatments were performed: 20- to 30-yr-old Norway spruce were completely released from self-propagated overstorey birch, or 500 birches ha(-1) were left as a shelter. After five growing seasons the plots were examined and the growth was calculated. The results showed a significant loss in spruce yield due to the shelter. However, in terms of volume the yield of birch wood in the shelter was almost three times the loss in spruce yield. The results also indicate that a shelter will, owing to increased one-sided competition, enhance the variation in height of the spruce.