Environment and evolutionary history depict phylogenetic alpha and beta diversity in the Atlantic coastal white‐sand woodlands

By Jhonny Capichoni Massante & Pille Gerhold

The Atlantic forest of South America is a regional mosaic of different habitat types. Yet despite this heterogeneity, rainforests have received far more attention in research than adjacent vegetation types. This is not surprising given that rainforests are one of the most imperilled habitats on our planet and a well acknowledged “biodiversity hotspot”. However, given the high prioritisation of rainforests in research and conservation, we risk to lose valuable biodiversity information on less well studied vegetation types.

Coastal white-sand woodlands, also known as restingas in Brazil, are a fundamental component of the Atlantic forest region as they occur along 3000 km of the Brazilian coast. Restingas have undergone rapid habitat loss due to human development, with more than 90% of their area altered or lost. Although highly diverse, restingas have fewer species than the adjacent rainforests. Their young evolutionary age could be one reason for their relatively low species richness. Restingas were formed in the Quaternary, as a result of marine deposits and changing sea-level dynamics. It is likely that the speciation time (time in which new species are originated) in restingas was too short compared to the much older rainforests. Therefore, most restinga species dispersed from adjacent rainforests and other vegetation types. Environmental constraints could be another reason for the relatively low species richness in this habitat type. Not all rainforest species can establish in restingas. High salinity, nutrient poor soils, drought, and flooding could have formed a strong filter for colonisation.

Despite the long history of research on restingas, we have very little understanding of their evolutionary history. In our published study, we investigated the richness of flowering tree species and their evolutionary relationship across the geographic distribution of restingas. Specifically, we aimed to analyse how species have assembled in response to environmental and evolutionary factors.

We found the highest number of species in the central distribution range of restingas, which coincides with an area known for its high endemicity (species unique to a region). Interestingly, the evolutionary relationships among species did not show the same pattern. In fact, co-existing species became more distantly related in the southernmost restingas. We hypothesise that forest remnants sustained relict species during climatic oscillations in the Quaternary, which were more pronounced in South Brazil. After oscillations subsided, restingas could have been colonised by species from forest remnants, including from Araucaria forests, and by species from geographically widespread plant families, thus creating restingas of distantly related species. On the other side of the geographic gradient, the co-existence of more closely related species in restingas may have resulted from environmental constraints which could have selected for stress-tolerant species. Furthermore, many species could have originated from endemics and a small set of families in adjacent forests, only colonising restingas nearby. That could have increased the evolutionary relatedness of species in restingas. Our results suggest that restingas could have undergone contrasting evolutionary history along their distribution range in Brazil.

This is a plain language summary for the paper of Massante & Gerhold published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12900). The post was prepared by Jhonny Capichoni Massante.