Simulations of the influence of forest management on wind climate on a regional scale

A linear PC-based airflow model Wind Atlas Analysis and Application Program (WAsP) is used here to study how forest management, especially clear-cutting, influences the local wind climate in terms of mean regional wind velocity and the local occurrence of high wind velocities, due to changes in surface roughness. Wind velocity variations are examined first at a management unit level of 64 km2 over the interval between two stand inventories (1990 and 2001) and secondly in a smaller area where new forest edges were created through different clear-cutting options. Results show that a change in landscape in terms of a decrease of approximately 17% in the area of old forests did not have any clear effect on regional mean wind velocity. However, under conditions of high wind velocity the change in surface roughness caused a locally significant increase in the windthrow risk. Furthermore, if clear-cutting are carried out as soon as the forest stands reach the minimum acceptable mean diameter (or stand age) this will increase the proportion of clear-cut areas and thus also the proportion of areas experiencing high wind velocities. However, the risk of windthrow does not necessarily increase as straightforwardly at the regional level if the vulnerable old stands are cut.