Mid-term evaluation of the success of riverbank restoration within the scope of the LIFE+ RIPISILVANATURA project

Riparian ecosystems are areas of great ecological interest, but their anthropic modification has led to the establishment of invasive species (Arundo donax L.) in the Segura River basin (SE of Spain), with detrimental effects on biodiversity. In view of the problems generated, giant reed control actions and plantations with native species were carried out within the LIFE+ RIPISILVANATURA project (2015-2019) in the Segura River middle reach. Here, we performed a medium-term biomonitoring (two years after the end of restoration measures and the thaw of maintenance actions, i.e., weed cutting) in 8 restored zones and compared with reference conditions to evaluate the degree of success achieved. Non-Metric Multidimensional Scaling (NMDS) and multivariate generalised linear models for abundance data (GLM) were used to detect spatial and temporal differences in species composition and abundance in revegetated and reference sites; and ANOVAs were applied to determine whether the mean height of planted species differed between restored areas with or without subsequent maintenance. In addition, temporal changes in different ecological indicators and the effects of the continuation or not of maintenance were examined using linear mixed effects models. Six years after the beginning of the actions and two years after the end of the project, the degree of success achieved was relatively low. Although the composition of riparian plant communities in restored zones turned more similar to reference ones, the absence of maintenance produced an increase in the cover, density, and height of A. donax as well as a decrease in species richness and poor riparian condition. Therefore, medium- to long-term maintenance actions and monitoring seems essentials to improve the success of future riparian restoration projects.