Reed between the lines: Terrestrial 3D laser scanning to assess recreational impacts on lakeshore vegetation

Swimming in lakes and spending time on the shore are popular summer activities, but as climate change continues and land use intensifies, pressure on lakeshore ecosystems is increasing. In particular, plants play an important role in these ecosystems by stabilizing the shoreline and providing habitat, but they suffer from trampling and destruction caused by human use. However, the effects of lakeshore recreation on plants are not well understood. To assess the impact of bathers on the reed bed and the area of the shoreline used for sunbathing, terrestrial laser scanning (TLS) was employed to analyze changes in the aboveground spatial distribution of plant material at very high spatial or temporal resolution. Measurements were taken before and after summer weekends at nine lakes in Brandenburg, Germany, and the occupancy status of voxels (i.e., cubic volume elements) in voxelized TLS point clouds of the lakeshore vegetation was compared. In addition, standardized visitor counts were conducted to determine the bathing sites' visitation rates. Over the course of a summer weekend, bathing and control sites displayed similar changes in total reed volume. The analysis has identified no clear relationship between the highly dynamic volume changes and the bathing activity along the gradient of visitor density that has been considered here. The variation of vegetation in the sunbathing area was generally small and showed no clear tendency for directed loss or gain after a weekend. As we studied established sites, the vegetation may have already adapted to human use. While the current visitor density and visitor behavior do not appear to be causing discernible changes, visitor management measures will be necessary if the intensity of use increases in the future.