Interactions among forestry regeneration treatments, plant vigour and browsing damage by deer.

In a large field experiment we studied the influence of regeneration methods on the extent to which roe deer (Capreolus capreolus L.) browse on spruce (Picea abies L. Karst) seedlings. Our objective was to evaluate if treatments that are good at stimulating regeneration may increase browsing damage by deer. Data were collected between 1993 and 1995, and in the winters of 1993-94 and 1994-95 the frequency of browsed seedlings was 13.2% and 13.4%, respectively. The frequency of browsing damage varied considerably between sites and clearcuts. Browsing damage was more frequent when the regeneration methods included insecticide treatments. Among insecticide-free treatments, browsing was heavier on scarified plots than on herbicide-treated or control plots (in which seedlings were planted on untreated ground and given no post-planting treatment). Containerised seedlings were browsed more than bare-rooted ones. Neither the age of clearcut when planting, nor removal of slash, had any effect on browsing. It was demonstrated that regeneration methods that increased plant vigour (as assessed by leader growth and needle colour index) led to more browsing damage. Thus, our results support the plant vigour hypothesis, which states that many herbivores prefer to feed on vigorous plants because they are more nutritious. However, the difference in browsing damage between containerised and bare-rooted seedlings could not be explained solely by the plant vigour hypothesis.