Abstract

Current efforts to restore and create ecosystems require greater understanding of ecosystems' responses to commonly used physical and biological intervention approaches to overcome ecological and technological limitations. We estimated effect sizes from measurements of biotic assemblage structure and biogeochemical functions at 628 restored and created wetlands globally, in comparison with 499 reference wetlands. We studied the recovery trajectories of wetlands where different restoration or creation approaches were used under different environmental settings. Although the variance explained by a linear mixed-effects models was low (6-7%), the study of recovery trajectories showed that the restoration or creation approach had no significant effects in most environmental settings. In particular, wetlands where surface modification and flow re-establishment were used followed similar recovery trajectories regardless of whether they were revegetated or not. We even found potential detrimental effects of biological manipulations on the recovery of the plant assemblage, particularly in cold climates and in wetlands restored or created in agricultural areas. Since physical interventions are required to recover or create the hydrological conditions of degraded or new wetlands, and given the high cost (22-73%) of biological interventions (i.e. revegetation), the need for biological interventions is, in most cases, unclear. Our results highlight the urgent need to increase our understanding of the long-term effects of restoration and creation actions in our aim to engage in large-scale ecosystem management strategies for wetlands.Synthesis and applications. These results suggest that, currently, the recovery and development processes of restored and created wetlands can be driven by spontaneous processes rather than by the response of wetlands to human interventions other than those targeted to restore hydrological conditions that existed prior to disturbance. However, given the synthetic nature of the data set, the mixed nature of available data and the limited number of measures we found to estimate recovery, caution must be exercised when adapting the results presented here to the planning and execution of specific ecosystem restoration projects. These results suggest that, currently, the recovery and development processes of restored and created wetlands can be driven by spontaneous processes rather than by the response of wetlands to human interventions other than those targeted to restore hydrological conditions that existed prior to disturbance. However, given the synthetic nature of the data set, the mixed nature of available data and the limited number of measures we found to estimate recovery, caution must be exercised when adapting the results presented here to the planning and execution of specific ecosystem restoration projects.