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![](https://www.spsnational.org/sites/default/files/fig2.png)
Figure 2. A calculation of the number of trees on earth using order-of-magnitude estimates. This calculation gives an area for earth of about 5 x 1014 m2. Assuming the earth is one-third land, the land is one-third trees by area, and each tree has a canopy area of 100 m2, we arrive at 5 x 1011 trees.