Understanding the World’s Forests

Collaborators from across the globe have conducted the most massive survey of trees ever. Their findings were published September 2 in their Nature article Mapping tree density at a global scale. Over 429,000 ground-level measurements were collected and correlated with maps of forest cover in each of the world’s major ecosystems. Interestingly, trees are found almost everywhere- billions of trees live in tundra, grasslands, and desert regions.

There is some very good news in this article; there are actually many more trees than previously thought- over 3 trillion! Linking these density maps with remotely acquired data describing climate, land use, topography and vegetation characteristics yielded more than just a census for trees. The model will lead scientists to a better understanding of how forests interact with the planet; sequestering carbon, filtering water, producing oxygen-and how different types of forests fill these roles differently.

The authors examined the correlation between tree density and several variables. They found that factors that are good for forests in one biome, might be deleterious in another. For example; while increased annual precipitation correlates with increased tree density in a tropical coniferous zone, it has the opposite effect in tundra. Only one factor consistently suppresses tree density in all of the 14 biomes studied: human development.

Using their model, along with a previously-estimated 192,000 square kilometers of forest loss (determined by observations of ground cover over time), researchers estimate that a staggering 15 billion trees are cut down each year, and that populations have declined by 46% since human civilization began. ‘The Billion Tree Campaign” may need to get even more ambitious.

For us, the beginning of human civilization is part of the distant past, but 10,000 years is nothing to trees, who evolved in the late Devonian period, at LEAST 385 million years ago. I was able to find a website with lovely maps from different periods of history. The world looked like this back then. No America, no mammals, no dinosaurs, not much of anything. But there were trees. Ten thousand years is a heartbeat on this scale. Is it any wonder then, that so many who are dependent on trees are struggling to cope with the sudden collapse in their numbers?

The Bengal tiger, western lowland gorilla, mountain gorilla, South China tiger,Javan rhino, saola, Amur leopard, and Sumatra’s tiger, rhino, elephant and orangutan; are all among the critically endangered list published by the IUCN. Many others have gone extinct already. The effects are less obvious on non-forest or ex-forest creatures such as ourselves. But even if we’re not living in them or eating them, I have a feeling we might find life quite difficult without them.

What might the world look like without trees? We might look to the world before trees for clues. Back to the Devonian, then. Amphibians were pretty much the latest and greatest that the world had managed to muster at that point. Amphibians are in much more serious peril than trees, so I think we can count them out. Reptiles, dinosaurs, birds, and mammals had not even thought about evolving yet. Would they be able to survive in the low-oxygen environment? I probably sound a bit alarmist, after all we have 3 trillion trees left! However, at 15 billion felled per year, it is well within our grasp to wipe them out.

Trees are cut down, in many cases, to clear land for expanding agriculture. This only makes sense if you believe that we are not growing plenty of food already, and ignore the piles of food that are tossed out or left to rot. Another tree-hungry industry is paper production. However, our government still subsidizes the delivery of some 100 billion pieces of junk mail every year.

Our power to do harm to the planet is racing against our ability to make prudent decisions. Let’s all consider this when we choose leaders and select products.
Today’s blog post is centered around a thought provoking article in Nature, it can be found here: 

T. W. Crowther, H. B. Glick, K.R.Covey et al. “Mapping tree density at a global scale”  Nature September 10, 2015 pp 201-205. Macmillan Publishers.