Past land-use and ecological resilience in a lowland Brazilian Atlantic Forest: implications for passive restoration

The ecological resilience of abandoned pastures has important implications for the potential of passive restoration in the Brazilian Atlantic Forest, especially in the face of the ambitious restoration targets for this biodiversity hotspot. In the present study, we aimed to investigate the influence of past land-use on natural regeneration in two secondary forests that established on abandoned pastures with different land use histories (Abandoned + Fire-15 years since the last fire event and Abandoned-36 years ago) in a lowland Brazilian Atlantic Forest. Both secondary forests exhibit low resilience for the three analyzed attributes: vegetation structure, richness, and species composition. Secondary forests affected by fire have the lowest values for species richness, aboveground biomass and leaf area index compared to old-growth forests. Secondary forests were dominated by Moquiniastrum polymorphum-Asteraceae, which was absent from the old-growth forests. Fire resistance, capacity to establish in nutrient-poor soils and efficient seed dispersal in human-modified landscapes are important attributes that may explain the dominance of this species. We demonstrate that even in sites considered appropriate for passive restoration a priori (e.g. located in a protected area, 36 years since abandonment and close to old-growth forests), secondary forests exhibited low aboveground biomass and communities were dominated by few species. Therefore, our results highlight the effects of past land-use on natural regeneration and suggest the necessity to use interventions such as enrichment plantings, nucleation techniques and assisted natural regeneration in order to accelerate forest restoration.