Better ways to restore river forests
River floodplain forests provide numerous invaluable services for humans; yet, what little remains of such ecosystems is poorly functional and fragmented. River forest restoration began in the 1980s, yet most such efforts suffer from unclear focus and lack of criteria for evaluating success or failure. The EU-funded ESFFORES (Evaluating success of floodplain forest restoration) project assessed the effectiveness of hitherto unevaluated programmes. The team also derived a set of universal success criteria. The criteria allowed determination of suitable indicators and the factors contributing to success or failure. Such an approach helped researchers to consider a wider range of spatial scales and times since restoration than conventionally would have been possible. Using a literature review, the team first examined restoration cases around the world in order to find improvements. Cases fell into five main categories, of which the most important was control of grazing. Indicators of success included biodiversity, structure and processes. Researchers confirmed that the published evaluations had been local and covered less than 5-6 years. The directions of change had been more frequently assessed than comparisons with controls. The team recommended broadening the assessment to obtain more informative comparisons. Project members also examined the case of the invasive Tamarix trees in southwestern United States river systems. ESFFORES joined a large collaborative study that monitored the vegetation response to control efforts. Results suggested that the control methods reduced dominance of the exotic species, more through weed control than the fostering of natives. The abundance of native river species was much lower in restored sites than in reference conditions, indicating an excessive focus on weed control instead of hydrology. Researchers assessed vegetation response to various restoration strategies at the Ebro river in Spain and the Garonne river in France. Channel widening produced plant communities similar to those in natural gravel bars, including new recruits of keystone species. However, floodplain excavation produced degraded states quite unlike pristine conditions. In both rivers, restorations similar to natural reference conditions resulted from hybrid poplars being allowed to resprout after clear-cutting. ESFFORES results have improved understanding of the dynamics of restoring riverine forests, which will support restoration programmes.
Keywords
River forests, forest restoration, floodplain, ESFFORES, vegetation response, weed control
