This article presents, for the first time, an overview of all known tree species by scientific name and country level distribution, and describes an online database—GlobalTreeSearch—that provides access to this information. Based on our comprehensive analysis of published data sources and expert input, the number of tree species currently known to science is 60,065, representing 20% of all angiosperm and gymnosperm plant species. Nearly half of all tree species (45%) are found in just 10 families, with the 3 most tree-rich families being Leguminosae, Rubiaceae, and Myrtaceae. Geographically, Brazil, Colombia, and Indonesia are the countries with the most tree species. The countries with the most country-endemic tree species reflect broader plant diversity trends (Brazil, Australia, China) or islands where isolation has resulted in speciation (Madagascar, Papua New Guinea, Indonesia). Nearly 58% of all tree species are single-country endemics. Our intention is for GlobalTreeSearch to be used as a t...

GlobalTreeSearch: The first complete global database of tree species and country distributions

There is growing interest among conservationists in biodiversity mapping based on stacked species distribution models (SSDMs), a method that combines multiple individual species distribution models to produce a community-level model. However, no user-friendly interface specifically designed to provide the basic tools needed to fit such models was available until now.
The “ssdm” package is a computer platform implemented in r providing a range of methodological approaches and parameterisation at each step in building the SSDM: e.g. pseudo-absence selection, variable contribution and model accuracy assessment, inter-model consensus forecasting, species assembly design, and calculation of weighted endemism.
The object-oriented design of the package is such that: users can modify existing methods, extend the framework by implementing new methods, and share them to be reproduced by others.
The package includes a graphical user interface to extend the use of SSDMs to a wide range of conservation scientists and practitioners.

https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/2041-210X.12841

SSDM : an R package to predict distribution of species richness and composition based on stacked species distribution models

New Caledonia is renowned as one of the world’s most significant biodiversity hotpots. The nutrient-deficiency and cations imbalances of ultramafic soils, which cover a third of the island, harbor a disproportionally high proportion of the plant diversity and endemism of New Caledonia. This review explores how ultramafic soils have influenced the exceptional endemism and richness of New Caledonia trough the concomitant occurrences of habitat patchiness, climatic instability, environmental gradient, and edaphic heterogeneity of ultramafic soils. We focus on the unique ‘maquis’ vegetation where selective pressures by nutrient deficiency and trace element surplus are at their acme. We aim to synthesize our current understanding of diversification and speciation of lineages that have been phylogenetically studied to date. Fragmentation of the peridotite mantle in isolated massifs, and as such spatial heterogeneity of ultramafic soils types, appear to promote plant endemism and speciation. Repeated independent dispersal events of pre-adapted species and persistence of paleo-endemic lineages have contributed to the phylogenetic diversity and the endemism of the ultramafic flora. Finally, historical climatic instability has caused shifts of rain forest species in refugia thereby favoring the extension of maquis species.

How did the ultramafic soils shape the flora of the New Caledonian hotspot

Increases in drought-induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P50 ) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P50 , along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P50 values ranging between -4.03 and -2.00 MPa with most species falling in a narrow range of resistance to embolism above -2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P50 . Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought-induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/pce.12859

Vulnerability to xylem embolism as a major correlate of the environmental distribution of rain forest species on a tropical island

Due to the impelling urgency of plant conservation and the increasing availability of high resolution spatially interpolated (e.g. climate variables) and categorical data (e.g. land cover and vegetation type), many recent studies have examined relationships among plant species distributions and a diversified set of explanatory factors; nevertheless, global and regional patterns of endemic plant richness remain in many cases unexplained. One such pattern is the 294 endemic vascular plant taxa recorded on a 1 km resolution grid on the environmentally heterogeneous island of Sardinia. Sixteen predictors, including topographic, geological, climatic and anthropogenic factors, were used to model local (number of taxa inside each 1 km grid cell) Endemic Vascular Plant Richness (EVPR). Generalized Linear Models were used to evaluate how each factor affected the distribution of local EVPR. Significant relationships with local EVPR and topographic, geological, climatic and anthropogenic factors were found. In particular, elevation explained the larger fraction of variation in endemic richness but other environmental factors (e.g. precipitation seasonality and slope) and human-related factors (e.g. the Human Influence Index (HII) and the proportion of anthropogenic land uses) were, respectively, positively and negatively correlated with local EVPR. Regional EVPR (number of endemic taxa inside each 100 m elevation interval) was also measured to compare local and regional EVPR patterns along the elevation gradient. In contrast to local, regional EVPR tended to decrease with altitude partly due to the decreasing area covered along altitude. The contrasting results between local and regional patterns suggest that local richness increases as a result of increased interspecific aggregation along altitude, whereas regional richness may depend on the interaction between area and altitude. This suggests that the shape and magnitude of the species-area relationship might vary with elevation. This work provides-for the first time in Sardinia-a comprehensive analysis of the influence of environmental factors on the pattern of EVPR in the entire territory, from sea level to the highest peaks. Elevation, as well as other environmental and human-related variables, were confirmed to be influencing factors. In addition, variations of EVPR patterns at regional-to-local spatial scales inspire next investigations on the possible interaction between elevation and area in explaining patterns of plant species richness.

/pdf/disentangling-the-influence-of-environmental-and-5g4zba0r6p.pdf

Disentangling the influence of environmental and anthropogenic factors on the distribution of endemic vascular plants in Sardinia.

This article focuses on the distribution of trees on a high-elevation tropical island of the New Caledonian archipelago. The aim was to determine how the variety of environments occurring on this island (in terms of elevation, rainfall, substrate and vegetation types) shapes the distribution of tree species. We analyzed the distribution of 702 native rainforest species through ca. 40,000 occurrence records and GIS environmental layers. Results showed that species exhibit high environmental tolerance while their distribution is spatially highly aggregated. We concluded that tree species distribution in New Caledonia is shaped by dispersal limitation rather than by environmental specialization.

distribution and richness on a high-elevation tropical island

There is a debate concerning the definition and extent of tropical dry forest biome and vegetation type at a global spatial scale. We identify the potential extent of the tropical dry forest biome based on bioclimatic definitions and climatic data sets to improve global estimates of distribution, cover, and change. We compared four bioclimatic definitions of the tropical dry forest biome–Murphy and Lugo, Food and Agriculture Organization (FAO), DryFlor, aridity index–using two climatic data sets: WorldClim and Climatologies at High-resolution for the Earth’s Land Surface Areas (CHELSA). We then compared each of the eight unique combinations of bioclimatic definitions and climatic data sets using 540 field plots identified as tropical dry forest from a literature search and evaluated the accuracy of World Wildlife Fund tropical and subtropical dry broadleaf forest ecoregions. We used the definition and climate data that most closely matched field data to calculate forest cover in 2000 and change from 2001 to 2020. Globally, there was low agreement (< 58%) between bioclimatic definitions and WWF ecoregions and only 40% of field plots fell within these ecoregions. FAO using CHELSA had the highest agreement with field plots (81%) and was not correlated with the biome extent. Using the FAO definition with CHELSA climatic data set, we estimate 4,931,414 km 2 of closed canopy (≥ 40% forest cover) tropical dry forest in 2000 and 4,369,695 km 2 in 2020 with a gross loss of 561,719 km 2 (11.4%) from 2001 to 2020. Tropical dry forest biome extent varies significantly based on bioclimatic definition used, with nearly half of all tropical dry forest vegetation missed when using ecoregion boundaries alone, especially in Africa. Using site-specific field validation, we find that the FAO definition using CHELSA provides an accurate, standard, and repeatable way to assess tropical dry forest cover and change at a global scale.

/pdf/global-tropical-dry-forest-extent-and-cover-a-comparative-4dte35davl.pdf

Global tropical dry forest extent and cover: A comparative study of bioclimatic definitions using two climatic data sets.

In the context of global change, tropical forests are increasingly affected by fires. Understanding the ecological processes driving forest recovery in fire-modified landscapes is a critical issue. We analyzed spatial and temporal (8 years) changes in functional and phylogenetic composition of tree communities during forest post-fire recovery in anthropogenic savannas. We used null models to infer the main assembly processes driving forest succession along three 90-m transects running from an advancing savanna-forest edge to forest interior in New Caledonia. We also evaluated if successional changes differed between large and small trees, or depended on the demography of remnant savanna trees. We found coordinated shifts from drought- and fire-resistance towards shade-tolerance strategies, involving leaf, stem, and architectural traits along transects. Our results indicate stronger environmental filtering and faster temporal changes in composition of young edge communities. In forest interior, our results suggest slower compositional changes, with an important role of light limitation in community assembly. These non-random patterns depended on both the decline of savanna trees and compositional changes among forest species. We also found contrasting community patterns depending on tree size, supporting a stronger influence of environmental filtering on small trees. Our work emphasized the dominance of deterministic assembly processes driving tropical forest post-fire succession. Our study suggests that fire and drought drive environmental filtering during early succession at the forest edge, entailing constraints on multiple functional dimensions. As succession progresses, light-limitation becomes a stronger driver of community assembly, and community composition becomes more stable in time. Our study provides insights for a better understanding of the processes guiding tropical forest succession in the particular context of post-fire forest recovery.

Thomas Ibanez

Papers

distribution and richness on a high-elevation tropical island

Global tropical dry forest extent and cover: A comparative study of bioclimatic definitions using two climatic data sets.

Drivers of tree community assembly during tropical forest post-fire succession in anthropogenic savannas