Effects of recreational use on restored urban floodplain vegetation in urban areas

Urban river restorations focus on restoring aquatic and riparian habitats, increasing flood protection, and enhancing recreational potential. The increased recreational value such newly created urban green spaces is a key benefit of these measures as urban riparian areas are highly valued for recreation. However, high recreational pressure may contribute to the loss of natural vegetation and of biodiversity in restored riparian sites. This study investigates the impact of different recreational intensities and use types on the vegetation structure and vegetation quality by documenting direct (foot-traffic, breaking of branches, stems and roots) and indirect damages (litter and excrements). The major results are fourfold. First, while the proportion of some vegetation types can be correlated to the recreational intensity, neither recreation intensity nor recreation types enhanced the colonization success of invasive species. However, monitoring data showed that human-induced disturbances such as hydro-morphological changes favor alien plant establishment. Second, the study suggests a tipping point for pioneer vegetation at around a density of one user per 10 m river stretch. Already at lower user densities, pressure from trampling can slow down vegetation development. Third, the results indicate that users prefer urban greening and gravel bar elements rather than natural vegetation. Finally, while intensity of direct damages on the vegetation are weakly correlated with the user density, indirect damages increase with the user density. This study concluded that the identification of user hotspots would be helpful in developing a resilient restoration design, which in addition to information about the sensitive vegetation types in relation to recreational users and nature friendly recreational behavior could decrease vegetation damages. In particular, younger recreational users should be targeted by environmental protection campaigns.