Do you ever wonder if we’d run out of trees? Seems like a ridiculous notion given that they seem to be growing nearly everywhere. Yet today satellites give us extraordinary views of Earth’s land cover. They clearly show that the trees, or more accurately the forests, are changing and the change may startle you.
First, let’s look at broad numbers. Currently, the Earth’s land cover could be set into thirds; a third is barren or glacier covered, a third is use by people for agriculture and a third is forest. A third is a huge amount, about 43 million square kilometres. While the forest area is huge, it’s a change. It’s only about half the forested area of pre-human days. And we’re continuing to decrease forested area by 0.2 million square kilometres each year. Hence, broadly speaking, in about 200 years the forests will be gone; that is, we’d run out of trees!
Probably all conservationists, and most people, want to keep forests. Not only do they harbour wildlife, they also rejuvenate Earth’s atmosphere. We can keep forests in two obvious ways. One way is to stop forest degradation. This is the aim of REDD+. The other is to grow forests, i.e. to plant trees. This is the aim of the Trillion Tree Initiative. Let’s look at the latter.
The Trillion Tree Initiative is for people to plant a trillion trees. Simple enough. But where do we plant them? Assume on average that a hectare can support 600 trees. Thus, a trillion trees would need about 17.5 million square kilometres of land, another huge amount! On the plus side, these trees would sequester carbon thus reducing atmospheric carbon dioxide. And they’d store about 7.3×1021 Joules of potential energy. On the negative side, the Earth has no available land area; all habitable land is already allocated. And we’re changing 0.2 million more square kilometres each year from forest cover to agriculture cover. Thus, planting a trillion trees won’t likely occur given our reliance on today’s agriculture and food industry methods.
What this exercise shows us is the mathematical simple yet realistic challenging way to save trees. Trees, much as with animals, need land to grow. As we change natural land cover to suite our needs, we reduce the number of trees. And yes, trees can go extinct. So, while we can run out of trees, are we willing to act to prevent this and to regrow forests?