Earlier this month, media outlets around the world covered a dramatic study in Nature finding that the world contains over 3 trillion trees — but that humans have nearly halved their numbers since the dawn of civilization. But much of the coverage missed what may have been the most fascinating new data of all, which the researchers, led by Thomas Crowther of Yale University, provided in a supplement to their broader study.
There, the scientists calculated comprehensive estimates of the numbers of trees in each country of the world, and how that relates to the country’s physical size, population size and more.
This research provides nothing less than an entirely different way of looking at the world — in terms of what you might call “tree wealth” or “tree resources.” After all, having lots of trees in a country provides a huge host of benefits — trees are both a natural resource and an asset to humans. They filter water, combat air pollution, sequester huge amounts of carbon that would otherwise reside in the atmosphere, and even, it appears, contribute to human psychological and health benefits. Indeed, large parts of the world population depend on forests for food.
And then, there’s just the emotional connection to nature. “I think people inherently value trees,” said Clara Rowe, a co-author of the study and a recent graduate of the Yale School of Forestry and Environmental Studies, by e-mail. “In the days since our study was published, we’ve heard from individuals all over the world who are concerned about forest resources in their countries.”
So what does the world look like when you examine it through this lens — taking a tree’s eye view, so to speak, of different countries?
We took the data provided by the researchers — with particular help from Rowe — and looked first at the total number of trees in countries across the world. These numbers are based upon the researchers’ “biome-level model,” which they note is more accurate at larger scales and less accurate at highly detailed resolutions.
“The accuracy of estimates will increase with the size of the country,” the researchers explain.
Based on this approach, the world’s overall tree leader is clearly Russia, with 642 billion total trees, followed by Canada with 318 billion and Brazil with 302 billion. The United States is actually fourth overall in this ranking, with 228 billion trees. Other countries with over 100 billion trees include China, with 140 billion and the Democratic Republic of the Congo, with 101 billion. Indonesia comes in 7th, with 81 billion, and Australia 8th, with 77 billion.
Such are the top 8 countries in the world for total trees — but it’s less clear what such an absolute ranking tells us. Clearly, having a vast size, as Russia does, helps ensure that a country also has a vast number of trees.
But there are other metrics for measuring tree wealth, too, ones that might be more revealing and less dependent on sheer size. For instance, consider the world’s “tree density” — the number of trees in a given country per square kilometer of the country’s area:
Desert countries naturally tend to show the lowest tree densities — Saudi Arabia and Qatar have 1 tree per square kilometer apiece. By contrast, among relatively large countries, Finland had 72,644 trees per square kilometer, and Sweden had 69,161. Also surprisingly tree dense: Slovenia, with 71,131 trees per square kilometer.
Such numbers may reflect the fact that, as the researchers put it in their paper, in “northern latitudes, limited temperature and moisture lead to the establishment of stress-tolerant coniferous tree species that can reach the highest densities on Earth.” There is more total forest in the tropics, they found, but it isn’t as dense. So the type of forest that a country fosters has a big influence on this metric.
Another way to look at the issue, though, is how a country’s tree numbers relate to its population. Just as we measure the per-capita wealth of a nation, we can measure its number of trees per person.
This metric revealed once again that vast northern countries like Russia and Canada are surprisingly “tree rich,” with thousands of trees per resident. There are a whopping 8,953 trees per person in Canada. But tropical countries of the southern hemisphere can also hold their own. Here, Bolivia (5,465 trees per person), Gabon (8,131), and the Central African Republic (5,152) also fared quite well.
By contrast, desert countries once again were quite low – Egypt was estimated to have only about 1 tree per person. The metric is also highly sensitive to population size, meaning that India, with a population of 1.27 billion and a tree population of only about 35 billion, had just 28 trees per person.
Very high tree-to-person numbers were clustered in the northeast of South America: Suriname had 15,279 trees per person, Guyana 14,692, and French Guiana a stunning 20,226. Of course, these countries all have populations under a million people.
So, are there any patterns in how many trees a country has, and in particular, do those patterns relate to its level of wealth or economic development?
It has often been suggested – most recently in a report from the United Nations’ Food and Agriculture Organization — that wealthier countries have more or a higher percentage of the world’s trees. This would seem to reinforce the notion that poorer countries tend to consume their tree resources in order to try to advance their economic growth (for instance, by converting forests into farmland), while wealthier countries have the luxury of preserving national parks or protected areas. Indeed, prior research has suggested that — at least within the United States — “higher income populations afford the expense of alternative land use, planting and maintaining of urban trees.”
The Nature researchers, however, disagree after examining their own data and metrics, with a focus on the density of trees, rather than their overall extent. In particular, Rowe ran an analysis of the link between the International Monetary Fund’s World Economic Outlook Groups — groupings of countries based on their economic status as well as their region — and the density of trees across these countries.
She found that while groups of emerging and developing countries (like “Latin America and the Caribbean” or “Developing Asia”) showed more variability in tree density than developed country groupings — “Euro Area” or “Major Advanced Economies” — it was not clear that there was any meaningful difference overall.
Rather, it was simply the case that one emerging country grouping, “Middle East, North Africa, Afghanistan and Pakistan” was quite low on trees — but then, that’s not surprising given the prevalence of desert in these countries. So it seems odd to relate this to economics, rather than simple geography. Simply put, some countries, due to their environments and climatic regimes, just can’t host as many trees as others.
“If you said to me, okay, the GDP per capita of Costa Rica is $8,000, I would have no way of telling you how many trees there are in Costa Rica or how dense those trees are,” said Yale’s Clara Rowe. She said that the most meaningful way of looking at the relationship between a country’s wealth and its tree resources would be to calculate a nation’s “forest potential” — how many trees it is actually capable of supporting — and then compare that with how many it actually has, which would then reflect how much the country has exploited those resources, as opposed to preserving them.
“That can really give us a better sense of what percentage of forest can be lost in every single country, and then maybe we can start relating that to things like GDP,” Rowe said. But the researchers haven’t done that analysis on a country-by-country level yet.
So in sum, looking at the world’s nations in the context of their “tree wealth” tells you some revealing things about them — even as it also throws into question some of our assumptions about the links between a country’s forests and its economic situation. As the world moves to fight climate change — and focuses more and more on restoring forests in order to do so — we can expect more research to provide a much more penetrating window on this relationship.
“Ultimately, we hope that our study encourages more specific metrics for understanding forest resources,” Rowe said by e-mail. “Countries should ask themselves: How old are our forests? How much carbon do they store? How diverse are our trees and the species they shelter? But for now, tree number is a great place to start.”