Responses of young Norway spruce (Picea abies) to winter browsing by roe deer (Capreolus capreolus): Effects on height growth and stem morphology

The effects of natural and simulated winter browsing by roe deer on mortality, growth and defects in tree form among young recently planted Norway spruces were studied in two field studies and one simulation (clipping) experiment. No effect of browsing or clipping on mortality was observed. However, height growth was reduced by browsing and clipping, and the reduction increased with increases in the number of years in which they were browsed or clipped. Browsing or clipping in three successive years reduced height growth by the equivalent of about 1 yr. Spruces frequently became multi-trunked and/or developed multiple leaders as long as browsing and clipping lasted. However, when the browsing or clipping ceased, almost all spruces became single-trunked again. A more persistent effect was that many of the multiple trunks developed into large, abnormal branches or "spike-knots". The characteristics of the spike-knots resulting from browsing and clipping were very similar to those caused by other types of damage. The results indicate that roe deer browsing on spruce is less harmful than many Swedish foresters have feared