Spruce and birch growth in pure and mixed stands in Sweden.
An experiment was established in a 38-year-old, mixed species stand with a 14.5-m birch overstory (Betula species) and a 3-m spruce understory (Picea abies). Treatments were birch shelterwood with 300 or 600 stems/ha and spruce understory with 1500 stems/ha, grown separately or mixed on 14 plots. Height growth of spruce was not significantly affected by birch shelterwood during a 36-year observation period, but spruce trees under birch shelter were more slender. Volume growth of spruce was slightly reduced by birch shelter, and volume growth of birch significantly reduced by a spruce understory. Total growth was higher for mixed than for single-species plots.