What remains to be discovered: A global assessment of tree inventory completeness

Aim: Recent unprecedented efforts to digitise and mobilise biodiversity data have resulted in the generation of “biodiversity big data”, enabling ecological research at scales previously not possible. Here, we evaluated the completeness of digitised tree records globally, and identified where future surveys should focus to maximise regional inventories. Location: Global. Methods: We analysed spatial patterns in tree records from the Global Biodiversity and Information Facility and assessed global tree inventory completeness at a 100 km resolution and the ecoregional scale. We also identified priority areas for future exploration by examining the spatial covariation of completeness and natural habitat and forest conditions. Results: Spatial patterns of sampling effort and tree inventory completeness are unevenly distributed around the world, with most well-known sites being concentrated in the Global North, whereas large areas in species-rich tropical regions remain poorly documented. Moreover, many sites with low inventory completeness coincided with areas of rapid natural habitat loss and low forest integrity. Main Conclusions: Digitised biodiversity data has great potential to help address ecology questions and inform conservation actions if their biases and uncertainties are understood. Here we illustrated how such data can be used to improve existing knowledge and identify priority areas for future surveys.