Mapping tree density at a global scale

Ground-sourced tree density data is assembled to provide a global map of tree density, which reveals that there are three trillion trees (tenfold more than previous estimates); tree numbers have declined by nearly half since the start of human civilization and over 15 billion trees are lost on an annual basis. Until now, our understanding of global forest ecosystems has been generated from satellite information that can tell us about the area of forest. Policy makers and environmental scientists have relied heavily on this information when considering trees' involvement in patterns of biodiversity, biogeochemical cycles and their contribution to ecosystem services. Thomas Crowther et al. have extended the scope of this information by generating a map of global tree density that reveals what is going on below the canopy. The map, which was generated using more than 400,000 ground-sourced measurements of tree density, reveals patterns in tree numbers at regional and global scales. Using this map, the authors are able to estimate that the current global tree number stands at approximately 3 trillion. See also News by Ehrenberg The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.30 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.66 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.