The tree flora of southeastern Brazilian Atlantic forests was investigated according to two main aspects: (a) the variations in floristic composition of bodi rain and semi‐deciduous forests were analyzed in terms of geographic and climatic variables by performing multivariate analyses on 125 existing floristic checklists; and (b) the links of both rain and semi‐deciduous forests to Amazonian forests and Cerrados (woody savanna) were assessed. All analyses were performed at the species, genus, and family levels. The information obtained for the 125 forest areas was organized into an environmental database containing geographic and climatic records, and a floristic database containing binary presence records for 2532 species, 520 genera, and 106 families. Canonical correspondence analyses (CCA) were utilized to assess the relationship between geographic and climatic variables, and tree flora composition. Venn diagrams and cluster analyses were used to assess the floristic links to Amazonian forests and Cerrados. The following patterns were detected at all three taxonomic levels: (a) the differentiation between rain and semi‐deciduous forests is floristically consistent and strongly correlated with rainfall regime, although transitions may be abrupt to gradual; (b) a north–south differentiation exists for both rain and semi‐deciduous forests, probably caused by variations in both temperature and rainfall regime; (c) The flora of semi‐deciduous forests also changes with increasing distance from the ocean and the associated increasing rainfall seasonality; and (d) elevation and associated temperatures are strongly correlated with the internal differentiation of both rain and semi‐deciduous forests. To a considerable extent, the tree flora of semi‐deciduous forests is a subset of the rain forest flora, probably extracting species that are able to cope with a longer dry season. There is greater floristic similarity at the species level between Atlantic rain and semi‐deciduous forests than between any of these and either Amazonian rain forests or Cerrados. Nevertheless, semi‐deciduous forests and Cerrados show stronger links, particularly at the generic and familial levels. Therefore, rhere is little floristic ground for viewing Atlantic rain forests as being closer to their Amazonian counterparts than to the adjacent semi‐deciduous forests. The most appropriate view of rain and semi‐deciduous forests in southeastern Brazil is that of a continuum in tree species distribution. We suggest that the definition of Atlantic forests should be as comprehensive as that of Amazonian forests.

This review suggests that the ecology and patchy global distribution of seasonally dry tropical forest (SDTF) has distinctively structured the evolutionary history and biogeography of woody plant groups that are confined to it. SDTFs have few widespread woody plant species causing high β-diversity between separate areas of forests. These separate areas contain geologically old, monophyletic clades of endemic plant species that often have geographically structured intraspecific genetic variation. These patterns of diversity, endemism, and phylogeny indicate a stable, dispersal-limited SDTF system. SDTF species tend to belong to larger clades confined to this vegetation, exemplifying phylogenetic niche conservatism, and we argue that this is evidence that the SDTF is a metacommunity (biome) for woody plant clades. That phylogenetic, population genetic, biogeographic, and community ecological patterns differ in woody plants from tropical rain forests and savannas suggests a hypothesis that broad ecological settings strongly influence plant diversification in the tropics.

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The floristic nature of central Brazilian forests, as well as their links to other main forest formations of eastern tropical South America, is assessed by means of multivariate analyses of 106 existing floristic checklists and by the analysis of a series of dot-maps showing the distribution of 55 woody species. Most species of central Brazilian forests seem to conform to two main distribution patterns: (1) species of deciduous and semideciduous forests are dependent essentially on the occurrence of patches of soils of intermediate to high fertility within the cerrado domain and tend to be distributed mostly along a northeast-southwest arch connecting the caatingas to the chaco boundaries; (2) considerable numbers of gallery forest species are dependent on high soil moisture and many appear to link the Amazonian and Atlantic rainforests by crossing the cerrado region in a northwest-southeast route via the dendritic net of gallery forests. Many gallery forest species are habitat generalists, some even occurring in the cerrado vegetation. Nevertheless, significant numbers of gallery endemics are also present. Galleries of the west and north of the Cerrado Province show stronger floristic links to the Amazonian rainforests, while those of the centre and south show stronger affinity with the montane semideciduous forests of southeastern Brazil. Present-day distribution patterns are discussed in the light of the current knowledge of palaeoenvironmental changes in the Neotropics.

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Seasonally dry tropical forests are distributed across Latin America and the Caribbean and are highly threatened, with less than 10% of their original extent remaining in many countries. Using 835 inventories covering 4660 species of woody plants, we show marked floristic turnover among inventories and regions, which may be higher than in other neotropical biomes, such as savanna. Such high floristic turnover indicates that numerous conservation areas across many countries will be needed to protect the full diversity of tropical dry forests. Our results provide a scientific framework within which national decision-makers can contextualize the floristic significance of their dry forest at a regional and continental scale. N eotropical seasonally dry forest (dry forest) is a biome with a wide and fragmented distribution, found from Mexico to Argentina and throughout the Caribbean (1, 2) ( Fig. 1). It is one of the most threatened tropical forests in the world (3), with less than 10% of its original extent remaining in many countries (4).Following other authors (5, 6), we define dry forest as having a closed canopy, distinguishing it from more open, grass-rich savanna. It occurs on fertile soils where the rainfall is less thañ 1800 mm per year, with a period of 3 to 6 months receiving less than 100 mm per month (5-7), during which the vegetation is mostly deciduous. Seasonally dry areas, especially in Peru and Mexico, were home to pre-Columbian civilizations, so human interaction with dry forest has a long history (8). The climates and fertile soils of dry forest regions have led to higher human population densities and an increasing demand for energy and land, enhancing degradation (9). More recently, destruction of dry forest has been accelerated by intensive cultivation of crops, such as sugar cane, rice and soy, or by conversion to pasture for cattle.Dry forest is in a critical state because so little of it is intact, and of the remnant areas, little is protected (3). For example, only 1.2% of the total Caatinga region of dry forest in Brazil is fully protected compared with 9.9% of the Brazilian Amazon (10). Conservation actions are urgently needed to protect dry forest's unique biodiversity-many plant species and even genera are restricted to it and reflect an evolutionary history confined to this biome (1).We evaluate the floristic relationships of the disjunct areas of neotropical dry forest and highlight those that contain the highest diversity and endemism of woody plant species. We also explore woody plant species turnover across geographic space among dry forests. Our results provide a framework to allow the conservation significance of each separate major region of dry forest to be assessed at a continental scale. Our analyses are based on a subset of a data set of 1602 inventories made in dry forest and related semi-deciduous forests from Mexico and the Caribbean to Argentina and Paraguay that covers 6958 woody species, which has been compiled by the Latin American and Caribbean Seasonally Dry Tropica...

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A key feature of life’s diversity is that some species are common but many more are rare. Nonetheless, at global scales, we do not know what fraction of biodiversity consists of rare species. Here, we present the largest compilation of global plant diversity to quantify the fraction of Earth’s plant biodiversity that are rare. A large fraction, ~36.5% of Earth’s ~435,000 plant species, are exceedingly rare. Sampling biases and prominent models, such as neutral theory and the k-niche model, cannot account for the observed prevalence of rarity. Our results indicate that (i) climatically more stable regions have harbored rare species and hence a large fraction of Earth’s plant species via reduced extinction risk but that (ii) climate change and human land use are now disproportionately impacting rare species. Estimates of global species abundance distributions have important implications for risk assessments and conservation planning in this era of rapid global change.