Modelling the cost of roe deer browsing damage to forestry

Models concerning economic impacts of mammals in forestry have hitherto been restricted to identifying predictive variables for the intensity and distribution of damage (in Europe and North America) or maximising the financial returns from hunting (in North America). This paper aims to quantify the financial costs and benefits of roe deer browsing damage in British forestry. When considering deer management in multiple-use forests, one of a foresterʹs aims may be to minimise the costs of deer damage. This paper provides a means to estimate these costs. The cost of roe deer browsing damage was calculated from the change in timber products associated with multiple-stemming of trees, increased establishment period, with associated costs, and rotation extension. The results suggest that browsing-induced reduction in timber quality (measured as the proportion of trees with multiple-stems at harvest) is not as economically important as some authors have suggested and can be tolerated at high levels (>=55%) if culling is the only method of deer control. Using a discount rate of 3%, the net present value (NPV) of 1 ha of yield class 14 Sitka spruce, including deer control but in the absence of deer damage, was estimated as GB£ 523 and dropped to GB£ 97 with all trees multiple-stemmed at harvest. The NPV did not begin to decline until 55% of the crop was multiple-stemmed at harvest. Extra years of establishment (with associated maintenance costs) caused by a loss of annual increment resulted in a more important economic effect of deer browsing. Establishment extension by 1 year resulted in a drop in NPV to GB£ 116 ha^-1. Establishment extension by 2 years resulted in an NPV of GB£ -287 ha^-1.