Single versus repeated human trampling events: Responses of ground vegetation in sub-urban beech forest

Aim Forests provide important ecosystem services and are often the only natural areas that are freely accessible to the public for outdoor recreation. Large numbers of forest visitors can cause severe damage to forest ecosystems, which in turn can affect the ecosystem functioning. We aimed to assess whether experimental short-term and long-term trampling affect the ground vegetation in deciduous forests and its recovery to a different extent. Location Beech forests in northwestern Switzerland. Methods We used a standard experimental trampling procedure to simulate single and repeated human trampling events of different intensity. Experimental trampling of different intensity was conducted on a single day (single trampling) or on five days at intervals of four weeks (repeated trampling) in three suburban beech forests on different soil types. We recorded the cover, height, species density and species composition of the ground vegetation in the trampling lanes. We also assessed the recovery of the ground vegetation one and two years after trampling. Results Trampling intensity and the type of trampling (single vs repeated) affected the ground vegetation in the three forests. Vegetation cover, plant height and species density all decreased with increasing trampling intensity, but to a different extent in the three forests. Most vegetation characteristics were more severely affected by repeated trampling than single trampling of equal intensity. A longer trampling period strengthened the effects of trampling on ground vegetation, except in one forest. Two years after experimental trampling, most vegetation characteristics still differed from those of undisturbed ground vegetation. Conclusion Our study revealed that both trampling intensity and the temporal distribution of trampling influenced the ground vegetation in temperate forests. We provide evidence that the temporal distribution of human trampling events is an important factor, which has to be considered in management decisions for natural beech forests.