There are just 3.04 trillion trees in the world, data from the first spatially continuous map of forest tree density suggests. The estimate of the ratio of trees per person is 422:1.
Though 3.04 trillion trees is an “order of magnitude higher” than previous estimate, the number of trees cut down each year is a staggering 15.3 billion and the global forest cover loss is approximately 192,000 sq. km per year. As a result, the global number of trees has reduced by as much as 46 per cent since the start of human civilisation. These are some of the results of a study published today in the journal Nature .
As per the study, a tree is defined as a “plant with woody stems larger than 10 cm diameter at breast height.”
Of the 3.04 trillion trees in the world, the tropical and subtropical forests have the highest number of trees at approximately 1.39 trillion (nearly 43 per cent), followed by boreal regions (0.74 trillion trees accounting for 24.2 per cent) and finally the temperate regions at 0.61 trillion trees (21.8 per cent). While the tropical forests have the highest number of trees, they have also witnessed the highest rate of tree loss.
Though the tropical forests have the highest number of trees, the tree density is highest in the forested regions of the Boreal and Tundra regions, the study notes. In the northern latitudes the deficient moisture and low temperatures allow only the stress-tolerant coniferous tree species to establish. The coniferous tree species, by default, reach highest densities.
Till date, scientists have relied on satellite images to provide estimates of global forest area. As a result, it was not possible to know the number of trees. For this study, T. W. Crowther, the first author from Yale University, Connecticut, U.S. and others used nearly 4,30,000 ground-sourced measurements of tree density from all the continents except Antarctica to generate a global map of forest trees.
Forested areas were found even in regions that are generally regarded as being bereft of them — deserts, tundra and grasslands.
Though warmth and water availability led to an increase in tree density, a negative relationship was found in many regions. For instance, in the case of flooded grasslands and tropical dry forests, the benefits of water availability did not result in increased tree density. This was because the forested land was put to agricultural use.
“The negative relationships between tree density and anthropogenic land use exemplify how humans contend directly with natural forest ecosystems for space,” they write. “Although the rates of forest loss are currently highest in tropical regions, the scale and consistency of this effect across all forested ecosystems highlight how historical land-use decisions have shaped natural ecosystems on a global scale.”
A dense forest greatly influences a vast array of biotic and abiotic processes, and the current data helps in providing insights into ecological dynamics. The data is also critical in guiding local, national and global reforestation/afforestation measures.