Do you know how many trees there are on Earth?
The previous estimate in 2008 was 400 billion, or 61 trees for every person.
Here, a new study used satellite imagery and tree counts on the ground to calculate there are 3 trillion trees on Earth.
This is 7 times the previous estimate and equates to 422 trees for every person.
The distribution around the world is determined by climate and human activity.
Highest tree density is in northern boreal and tundra forests (e.g. Scandinavia, North America), as well as tropical areas, which contain 43% of the planet’s trees.
But it’s not all good news. 15 billion trees are being cut down each year and we have lost nearly half of the World’s trees since farming began around 12,000 years ago.
Do you want more information?
Background
Trees are essential components of many diverse ecosystems around the world.
They provide shelter, carbon sequestration, oxygen production, food, water quality control and protection against erosion, amongst other benefits.
However, their usefulness for construction timber and fires (cooking, warmth), as well as competition for farming land, means they have been cleared by humans for thousands of years.
Knowing how many trees there are in the world and where they are would help policy makers manage the world’s forests against competing pressures.
A previous estimate of 400 billion trees in 2008 was thrown into doubt when a later study found 390 billion trees in the Amazon basin alone.
So how many trees are there in the world?
Materials and Methods
This study used 429,775 ground-source measurements, as well as satellite imagery, of tree density from every continent on Earth (except Antarctica) to generate a global map of forest trees. This provided a global tree density map at 1 km2 resolution. Trees were defined as plants with woody stems larger than 10 cm in diameter at breast height.
Results
This study estimates there are 3.04 trillion trees in the world, equating to 422 trees for each of the 7.2 billion people on Earth.
This is 7 times the previous estimate of 400 billion trees (in 2008), and is also more than the number of stars in the Milky Way galaxy.
1.39 trillion trees (46%) are in tropical and subtropical regions, 0.74 trillion (24%) in boreal regions and 0.61 trillion (22%) in temperate regions.
Tree density generally increases with temperature, with moist, warm conditions optimal for tree growth.
A negative relationship between tree density and moisture availability was discovered. It is most likely due to competition for productive land between forests and farming.
Current global forest clearing rates are estimated to be 15.3 billion trees or 192,000 km2 cleared each year, with the highest being in tropical regions.
Since the onset of human civilisation and farming (around 12,000), it is estimated that Earth’s tree numbers have fallen by 45.8%.
Discussion
It is hoped this survey of tree numbers will help policy makers manage the forests better, especially against powerful competing interests like agriculture and timber industries.
Article
Mapping tree density at a global scale
Crowther et al., 2015 Nature 525: 201-5
Keywords
Science, Earth, World, planet, biology, ecosystem, tree, forest, rainforest, plant, agriculture, timber, wood, tropical, boreal
Subject
ST1-8ES, ACSSU019, ST1-9ES, ACSSU032, ST1-11LW, ACSSU211, ST2-8ES, ACSSU075, ST2-11LW, ACSSU073, SC4-13ES, ACSSU116, SC5-13ES, ACSSU189