Trees are among the largest and most widespread group of organisms, essential to ecosystem stability and services, and supporting a wealth of terrestrial biodiversity. Knowledge of the number of tree species in the world, however, is limited, relying on expert opinions and checklists with uneven geographic coverage.
In an attempt to provide an estimate of the actual number of tree species on Earth, a large multinational team of researchers collaborated on compiling and curating a new comprehensive dataset that combines plot data from the Global Forest Biodiversity Initiative with species occurrences from GBIF and several other aggregators.
Based on the new dataset, which contained more than 64,000 named species, the authors calculated the potential global and continental tree species richness, arriving at an adjusted estimate of ~73,000 species. This result implied that more than 9,000 tree species remain to be discovered and described.
At the continental level, the authors estimated that about 43 per cent of all Earth's tree species occur in South America, suggesting a gap of almost 4,000 species currently unknown to science. Globally, as many as 40 per cent of species were likely rare, comprised of few populations and small distributions.
Between two thirds of all known species occurred in tropical and subtropical moist forest biomes across all continents. The study estimated that hotspots of undiscovered species may exist in such undersampled regions.
With anthropogenic land use and climate change disproportionally threatening rare species, the study provides valuable insights into the vulnerability of global forest biodiversity, essential to informing and prioritizing forest conservation efforts worldwide.