Investigations on the effects of game browsing on surface runoff in Alpine forests

Abstract The hydrological effect of forests on reducing surface runoff and therefore mitigating flood hazards is well recognized in theoretical concepts, however its quantification for practical applications remains a challenge. Changes in the hydrological effect due to changes in the forest can be measured but hardly predicted, which makes it difficult to assess the impact of disturbances and management in protections forests against flood hazards. Game browsing is recognized as a problematic disturbance in protection forests that can impact the protective effect against gravitational hazards in the long term while its impact on the protective effect against flood hazards is yet poorly understood. Protection fences that exclude game browsing in the forest offer an opportunity to investigate its influence on the formation of surface runoff with paired rainfall experiments. They show distinct differences in the runoff formation for all investigated sites which can be attributed to the browsing exclusion by the protection fences. The surface runoff is up to three times lower inside compared to outside the fenced areas. Furthermore there is a systematic difference in the measured soil properties for all investigated sites. The hydraulic conductivity is clearly greater while the soil porosity, the topsoil depth and the humus height are slightly greater inside compared to outside the fenced areas. A statistical analysis of the surface runoff shows, that the measured differences are significant and that the factor of the protection fence is more important than the soil variabilities and the experiment conditions. This analysis reveals a clear trend of how the exclusion of game browsing within affects soil properties and reduces surface runoff. The differences in the soil properties are in line with the differences in the surface runoff and provide a physical basis for an explanation. The experiment design indicates that the differences in the soil properties are related to the game browsing, even if a detailed explanation of this relationship is missing. Nevertheless, it can be concluded from this investigation that the exclusion of game browsing can significantly decrease surface runoff therefore and impair the protective effect against flood hazard in the short term.