Extinction threshold for woody plants and regime shift in a biodiversity hotspot

AbstractLoss of natural habitats is the main cause of global biodiversity decline. This process has led to local extinctions of different species, in some cases abruptly, revealing threshold responses. Such thresholds may be associated with a loss of resilience, representing a regime shift between two alternative states. In recent years, studies have reported the occurrence of thresholds in various biological groups sensitive to deforestation. However, the occurrence of an extinction threshold for a completely super-diverse community, such as rainforest woody plants, remains unknown. We aimed to assess the influence of habitat quantity on the richness of woody plants in fragmented landscapes of the Atlantic Forest. Eleven landscapes with different proportions of habitat (between 5–60%) were studied in different parts of the northern Atlantic Forest (Bahia, Brazil). In each landscape, eight plots of 250 m² were established and branches of individuals with a circumference at breast height (CAP) ≥ 8 cm were collected. An extinction threshold was observed for the entire community, about 30% of the remaining habitat. When the richest families were considered, species loss occurred both linearly and at the threshold. The occurrence of the threshold in a super-diverse community without turnover suggests a regime change triggered by habitat loss. We discuss the implications of this knowledge for the management of human-modified landscapes, guiding strategies aimed at maintaining or restoring native vegetation above the threshold.