Environment and landscape rather than planting design are the drivers of success in long-term restoration of riparian Atlantic forest

QuestionIdentifying the factors that lead to the success of restoration projects has been a major challenge in ecological restoration. Here we ask which factors, aside from time since restoration began, drive the recovery of tree biomass, density and richness of the understorey in riparian forests undergoing restoration. LocationSemideciduous Atlantic Forest with tropical climate and deep, fertile soils, southeast Brazil. MethodsWe sampled tree basal area (DBH5cm), density and richness of the understorey (DBH<5cm) in 26 riparian forests undergoing restoration (a chronosequence spanning 4-53years). We assessed the following variables as possible factors, besides time, influencing community attributes: (1) planting design: density and richness of seedlings planted; (2) landscape features: proximity index measuring forest cover within a 1.5-km radius, distance and size of the nearest forest remnant; and (3) environmental factors: invasive grasses, soil fertility, drought, average annual precipitation and proportion of fine particles in the soil. We performed correlation analyses including predictor and response variables, followed by stepwise backward regression (AIC), multiple and simple linear regressions, to investigate the relationships between those factors and the community attributes. ResultsTree basal area was primarily influenced by the proportion of small particles in the soil (+) and secondarily by rainfall (-). Understorey richness was influenced by the combination of size (+) and distance (-) of the nearest patch, rainfall (-) and soil fertility (+). Understorey density was primarily influenced by the size of the nearest forest remnant (+) and secondarily by invasive grasses (-). No influence of density or richness of the seedlings planted was observed. ConclusionEnvironmental factors and landscape configuration drive the recovery of tree biomass, density and richness in communities undergoing restoration. The most relevant ecological filters influencing restoration success are availability of soil water and nutrients and the distance and size of the nearest remnant of native vegetation. The expected influence of richness and density of seedlings planted, considered for many years as important drivers of forest restoration success, was not confirmed in this study.