Application of a new method for assessing deer damage in forests: towards a diagnosis of their silvicultural impact

Abstract

A survey of deer (Capreolus capreolus, Cervus elaphus) damage to commercial forestry was carried out in 5 French regions. Browsing damage by deer on a large sample (n = 638) of vulnerable stands (planted and naturally regenerated) was recorded during 1999 using standard field measurement techniques. The main regenerated tree species were: oaks, beech, maritime pine, Douglas fir, silver fir ...We tried to set guidelines for an objective diagnosis of the future development of each inspected stand. Our evaluation was based on the number of undamaged or slightly damaged species, which was compared to the target value. Using this procedure, the stands were classified into 3 categories according to the silvicultural goal: not affected, temporarily or definitively affected. An analysis of the causes that led to the observed situation was carried out in order to detect the responsibility of deer compared to other factors. Results are discussed for our total sample and for 2 specific naturally-regenerated study sites which were more or less heavily grazed by deer. The impact of ungulates depends on the forest management, the species composition, the browsing tolerance of plants and the duration of the browsing pressure. Forecasting browsing damage effect appears to be more difficult in natural regeneration than in artificial regeneration. Variations in the density and the height of the seedlings in a same stand and the causes of a lack of seedlings explain the difficulty in evaluating game damage. These diagnoses were based on certain assumptions but still provide the managers with a useful tool for an objective assessment of damage. Other indicators and long-term studies are needed to support objective judgements.