The International Tree-Ring Data Bank (ITRDB) revisited:
Data availability and global ecological representativity
Aim: The International Tree-Ring Data Bank (ITRDB) is the most comprehensive database of tree growth. To evaluate its usefulness and improve its accessibility to the broad scientific community, we aimed to: (i) quantify its biases, (ii) assess how well it represents global forests, (iii) develop tools to identify priority areas to improve its representativity, and iv) make available the corrected database.
Location: Worldwide.
Time period: Contributed datasets between 1974 and 2017.
Major taxa studied: Trees.
Methods: We identified and corrected formatting issues in all individual datasets of the ITRDB. We then calculated the representativity of the ITRDB with respect to species, spatial coverage, climatic regions, elevations, need for data update, climatic limitations on growth, vascular plant diversity, and associated animal diversity. We combined these metrics into a global Priority Sampling Index (PSI) to highlight ways to improve ITRDB representativity.
Results: Our refined dataset provides access to a network of >52 million growth data points worldwide. We found, however, that the database is dominated by trees from forests with low diversity, in semi-arid climates, coniferous species, and in western North America. Conifers represented 81% of the ITRDB and even in well sampled areas, broadleaves were poorly represented. Our PSI stressed the need to increase the database diversity in terms of broadleaf species and identified poorly represented regions that require scientific attention. Great gains will be made by increasing research and data sharing in African, Asian, and South American forests.
Main conclusions: The extensive data and coverage of the ITRDB shows great promise to address macroecological questions. To achieve this, however, we have to overcome the significant gaps in the representativity of the ITRDB. A strategic and organized group effort is required, and we hope the tools and data provided here can guide the efforts to improve this invaluable database.
Journal of Biogeography. 2018. doi: 10.1111/jbi.13488
