Windborne: Can liverworts be used as indicators of altitudinal gradient in the Brazilian Atlantic Forest?

Abstract

Liverworts are non-vascular cryptogamic plants with wide geographic distributions due to their capacity to disperse their spores over long distances, although they have no epidermal cuticle, sensitive to external environmental conditions, found only in very specific microenvironments – and are therefore widely used as bioindicators. We evaluated the floristic composition of liverworts in localities located in different Atlantic Forest vegetation types in southeastern Brazil to address the following questions: Is the liverwort flora distributed uniformly or randomly, or does it demonstrate environmental niche restrictions at regional scales? If the distribution of liverworts is deterministic, do geoclimatic variables act as environmental filters for this flora? Can liverwort species be considered bioindicators of the different Atlantic Forest vegetation types? We undertook floristic surveys in 26 localities to evaluate the beta diversity of the liverwort flora and its correlation with environmental gradients (geoclimatic variables) using multivariate analyses and the Mantel Test. Ordination and classification methods indicated elevated beta diversity in a deterministic distribution of the liverwort flora along the Atlantic coast of southeastern Brazil. Altitude was significantly associated with the first axis of the CCA, demonstrating a floristic gradient between Lowland Forests and High Montane Forests and “Campos de Altitude”. Five floristic groups were identified and 34 species could be considered bioindicators. The principal geoclimatic variables that explained the floristic groupings of liverwort species were altitude, temperature, and precipitation. The prediction that liverwort plants demonstrated environmentally determined distributions was confirmed by the Mantel Test (rM 0.557; p<0.0001). Our results support the idea that the liverwort flora of the coastal Atlantic Forest in southeastern Brazil comprises part of a regional pool of species whose establishment and survival are determined by abiotic filters acting in those habitats. The low similarities between localities and the high numbers of indicator species suggest that the liverwort vegetation has a deterministic distribution at the regional level – which corroborates their use as bioindicators of vegetation types and of environmental conditions. Although species distributions are principally determined by environmental niches, geographical distances (dispersal limitation) are important in regions such as oceanic islands and coastal mountains.