A new study has just provided the most accurate calculation yet, and the results are surprising, for better and for worse. Until now, it was thought that there are 400 billion trees on the entire planet, or 61 per person. The count was based on satellite images and estimates of the forest area, but not on field observations. Then, in 2013, studies based on direct counts confirmed that in the Amazon alone there are almost 400,000 million trees, so the question remained in the air. And it is crucial to understand how the planet works globally, especially the carbon cycle and climate change, but also the distribution of animal and plant species or the effects of human activity on all of them.
The new count, published today in the journal Nature, shows that there are actually three trillion trees on the entire planet, about eight times more than previously calculated. On average there are 422 trees for every human.
The account by country reveals a huge inequality, with the rich like Bolivia, with more than 5,000 trees per person, and the solemn poor like Israel, where they barely touch two. Much of the contrast is due to natural factors such as climate, topography, or soil characteristics, but also to the unmistakable effect of civilization. The more the human population increases, the more the tree count decreases. It is partly explained because vegetation thrives where there is more humidity, the places that humans also prefer to establish farmland.
The work estimates that, each year, human activities kill 15,000 million trees. The net loss, offsetting the appearance of new trees and reforestation, is 10,000 million copies. Since the beginning of civilization, the number of trees on the planet has been reduced by 46%, almost half of what there was, indicates the study, published today in Nature.
If this rate of destruction continues unchanged, the trees will disappear from the planet in 300 years. They are three centuries, about 12 generations. "That is the time left if we do nothing, but we are hopeful that we can slow down and increase reforestation in the coming years to alleviate the human impact on ecosystems and climate," explains Thomas Crowther, researcher at the Yale University (USA) and first author of the study.
Two years ago, representatives of the UN's “Billion Tree Campaign” to replant some of the lost vegetation needed to know how much impact their efforts were having. They contacted Crowther, who works at the Yale School of Forestry and Environmental Studies, to ask how many trees there are in the world and how many in the different regions where they work. It was the beginning of the present study, signed by 38 researchers from 14 countries. Together they collected forest density data taken at more than 400,000 points on every continent except Antarctica. They divided the Earth into 14 types of biomes, or bioclimatic landscapes, estimated the density of trees in each of them based on satellite images, and tested their reliability with measurements on the ground. Finally they composed the most accurate global tree map ever made, with each pixel being one square kilometer.
The results show that the highest tree density is found in boreal forests and sub-arctic regions of Russia, Scandinavia and North America. The largest area of forest is in the tropics, with 43% of all the trees on the planet. The northern forests only contain 24% of the total number of specimens and 22% are in temperate zones.
Europe is one of the worst hit areas. "Before civilization, all of Europe was a large forest, but human pressure due to agricultural, industrial and urban development make this region one of the most deforested in the world," Crowther details. In Spain there are 11.3 billion trees, 245 per person.