Forest development in relation to ungulate grazing: a modeling approach

A dynamic simulation model describing long-term forest development under di fferent grazing pressures is presented as an illustration of system analysi s in forest grazing research. In this paper, a brief description of the mod el is presented as are some simulation results. The FORest GRAzing model (F ORGRA) simulates monthly changes in the characteristics of herbaceous under story and individual trees in plots, based on underlying physiological proc esses. Special attention is paid to the simulation of diet composition in r elation to ungulate species, food quality and food availability, and accoun ting for seasonal variation in there factors. The model is parameterized fo r 12 tree and shrub species, six species of the ground flora and four ungul ate species: roe deer (Capreolus capreolus), red deer (Cervus elaphus), Hig hland cattle (Bos taurus) and Konik ponies (Equus caballus). The results pr esented in this paper concern the development of a pine forest (Pinus sylve stris L.) in the Netherlands under various grazing pressures over a period of 100 years. They show that even low densities of ungulates can have signi ficant impacts on the regeneration and thereby on forest development. it is argued that this approach is generally applicable in forest grazing resear ch, providing a means for quantitative interpretation of the interaction be tween herbivory and forest development. (C) 1999 Elsevier Science B.V. All rights reserved.