Mapping Tree Density at a Global Scale. Crowther, T. W., Glick, H. B., Covey, K. R., Bettigole, C., Maynard, D. S., Thomas, S. M., Smith, J. R., Hintler, G., Duguid, M. C., Amatulli, G., Tuanmu, M. N., Jetz, W., Salas, C., Stam, C., Piotto, D., Tavani, R., Green, S., Bruce, G., Williams, S. J., Wiser, S. K., Huber, M. O., Hengeveld, G. M., Nabuurs, G. J., Tikhonova, E., Borchardt, P., Li, C. F., Powrie, L. W., Fischer, M., Hemp, A., Homeier, J., Cho, P., Vibrans, A. C., Umunay, P. M., Piao, S. L., Rowe, C. W., Ashton, M. S., Crane, P. R., & Bradford, M. A. 525(7568):201–205.
Mapping Tree Density at a Global Scale [link]Paper  doi  abstract   bibtex   
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 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 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. [Excerpt: Discussion] The global map of tree density can facilitate ongoing efforts to under-stand thogeochemical Earth system dynamics by incorporating ecosystem features that relate to elemental cycling rates. For eample, tree abundance can help to explain some of the variation in carbon storage and productivity within ecosystem types, but the strength of these effects remain untested across biomes. We assessed the relationship between tree density and plant carbon storage at a global scale by regressing our plot-level tree counts against modelled estimates A plant biomass carbon in those sites. This revealed a positive effect of tree density on plant carbon storage (Pc 0.001). However, the strength of the relationship is weak (r2 = 0.14), reflecting the vast array A local ecological forces that can obscure such global trends. For example, the effect of tree demityis likely to interact strongly with tree size. Larger trees contain the greatest proportion of carbon in woodlands, but the highest tree densities within a given ecosystem type are often associated with young or recovering forests characterized by many small trees. A thorough understanding of total vegetative carbon storage requires infonnation about both the size and the number of individual trees. [\n] A dense forest environment is a fundamentally different ecosystem from a sparse one and this influences a vast array of biotic and abiotic processes. Current remote sensing tools capture some, but not all of this information. The tree density Layer that we provide can there-fore augment the currently available layers by providing unique insights into ecological dynamics that are not represented by esti-mates of forest cover or biomass. It can inform biodiversity esti-mates and species distribution models by capturing perceivable environmental characteristics that determine habitat suitability for a wide variety of plants and animals. Baseline estimates of tree populations are also critical for projecting population- and commun-ity-level tree demographics under current and future climate change scenarios, and for guiding local, national, and international reforestation/afforestation efforts. Finally, by allowing us to compre-hend the global forest extent in terms of tree number, this map contributes to our fundamental understanding of the Earth's terrestrial system.
@article{crowtherMappingTreeDensity2015,
  title = {Mapping Tree Density at a Global Scale},
  author = {Crowther, T. W. and Glick, H. B. and Covey, K. R. and Bettigole, C. and Maynard, D. S. and Thomas, S. M. and Smith, J. R. and Hintler, G. and Duguid, M. C. and Amatulli, Giuseppe and Tuanmu, M. N. and Jetz, W. and Salas, C. and Stam, C. and Piotto, D. and Tavani, R. and Green, S. and Bruce, G. and Williams, S. J. and Wiser, S. K. and Huber, M. O. and Hengeveld, G. M. and Nabuurs, G. J. and Tikhonova, E. and Borchardt, P. and Li, C. F. and Powrie, L. W. and Fischer, M. and Hemp, A. and Homeier, J. and Cho, P. and Vibrans, A. C. and Umunay, P. M. and Piao, S. L. and Rowe, C. W. and Ashton, M. S. and Crane, P. R. and Bradford, M. A.},
  date = {2015-09},
  journaltitle = {Nature},
  volume = {525},
  pages = {201--205},
  issn = {1476-4687},
  doi = {10.1038/nature14967},
  url = {https://doi.org/10.1038/nature14967},
  abstract = {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 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 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.

[Excerpt: Discussion] The global map of tree density can facilitate ongoing efforts to under-stand thogeochemical Earth system dynamics by incorporating ecosystem features that relate to elemental cycling rates. For eample, tree abundance can help to explain some of the variation in carbon storage and productivity within ecosystem types, but the strength of these effects remain untested across biomes. We assessed the relationship between tree density and plant carbon storage at a global scale by regressing our plot-level tree counts against modelled estimates A plant biomass carbon in those sites. This revealed a positive effect of tree density on plant carbon storage (Pc 0.001). However, the strength of the relationship is weak (r2 = 0.14), reflecting the vast array A local ecological forces that can obscure such global trends. For example, the effect of tree demityis likely to interact strongly with tree size. Larger trees contain the greatest proportion of carbon in woodlands, but the highest tree densities within a given ecosystem type are often associated with young or recovering forests characterized by many small trees. A thorough understanding of total vegetative carbon storage requires infonnation about both the size and the number of individual trees. 

[\textbackslash n] A dense forest environment is a fundamentally different ecosystem from a sparse one and this influences a vast array of biotic and abiotic processes. Current remote sensing tools capture some, but not all of this information. The tree density Layer that we provide can there-fore augment the currently available layers by providing unique insights into ecological dynamics that are not represented by esti-mates of forest cover or biomass. It can inform biodiversity esti-mates and species distribution models by capturing perceivable environmental characteristics that determine habitat suitability for a wide variety of plants and animals. Baseline estimates of tree populations are also critical for projecting population- and commun-ity-level tree demographics under current and future climate change scenarios, and for guiding local, national, and international reforestation/afforestation efforts. Finally, by allowing us to compre-hend the global forest extent in terms of tree number, this map contributes to our fundamental understanding of the Earth's terrestrial system.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13746629,~to-add-doi-URL,featured-publication,forest-resources,global-scale,historical-perspective,modelling,regression,tree-density},
  number = {7568}
}
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