Restoration of riparian vegetation: A global review of implementation and evaluation approaches in the international, peer-reviewed literature.

We examined how restoration of riparian vegetation has been implemented and evaluated in the scientific literature during the past 25 years. A total of 169 papers were read systematically to extract information about the following: 1) restoration strategies applied, 2) scale of monitoring and use of reference sites, 3) metrics used for evaluation, and 4) drivers of success. Hydro-geomorphic approaches (e.g., dam operations, controlled floods, landform reconfiguration) were the most frequent, followed by active plant introduction, exotic species control, natural floodplain conversion and grazing and herbivory control. Our review revealed noteworthy limitations in the spatio-temporal approaches chosen for evaluation. Evaluations were mostly from one single project and frequently ignored the multi-dimensional nature of rivers: landscape spatial patterns were rarely assessed, and most projects were assessed locally (i.e., ≤meander scale). Monitoring rarely lasted for more than six years and the projects evaluated were usually not more than six years old. The impact of the restoration was most often (43%) assessed by tracking change over time rather than by comparing restored sites to unrestored and reference sites (12%), and few projects (30%) did both. Among the ways which restoration success was evaluated, vegetation structure (e.g., abundance, density, etc.) was assessed more often (152 papers) than vegetation processes (e.g., biomass accumulation, survival, etc.) (112 papers) and vegetation diversity (78 papers). Success was attributed to hydro-geomorphic factors in 63% of the projects. Future evaluations would benefit from incorporating emerging concepts in ecology such as functional traits to assess recovery of functionality, more rigorous experimental designs, enhanced comparisons among projects, longer term monitoring and reporting failure.