Equilibrium has to be found between maximizing social profit and minimizing ecological disturbance in open (acussible) nature reserves in the northern part of Belgium. Because the probability of disturbance grows with increasing visit density and frequency, some nature reserves tend to lose their specific quality. The aim of this study is, based on observation of visitors in a nature reserve, a detailed survey and selected spread models, to estimate the probability of off track visit of any location in a nautre reserve on deliberate times and in specific terrain conditions. This will lead to an impact assessment and management tool.