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Three Trillion Trees

A photograph of trees in the Meridon Forest in Central France. Image: NaturphilosophieGreen Planet

Once upon a time, Europe was almost covered by one giant forest.  Now, it’s almost entirely fields and grasslands.  Humans are controlling tree densities.  Understanding the global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere.

According to a new assessment published in the journal Nature, there are just over three trillion trees on Earth.  The figure is eight times bigger than the previous estimate, which counted perhaps 400 billion at most.

From studies that consider animal and plant habitats for biodiversity reasons, to new models of the climate, the more refined number will now form a baseline for a wide range of research applications.  Because trees play an important role in removing the greenhouse gas carbon dioxide from the atmosphere.

 

Mapping Tree Density on a Global Scale

Neither good news nor bad news, the new number simply describes the state of the global forest system in numbers that people can understand and scientists can use, and that environmental practitioners or policymakers can both understand and use.  At the heart of the new estimate is the greater use of ground-truth data.

A map showing the distribution of the Boreal Forest on Earth. Source: National Geographic
Earth’s Green Crown – A single ecosystem rings the north, shaped by fire, Arctic weather fronts, and the movements of long-vanished glaciers. According to boreal activist Don Sullivan, “You could walk across Alaska and Canada, Scandinavia and Siberia, and always be in the same forest.”  Source: National Geographic

The team collected tree density information from over 400,000 forest plots around the World – including many national forest inventories and a whole host of peer-reviewed studies where workers actually went out on the terrain and counted the number of trunks in a given area for a given forest type.

Out of approximately 3,040,000,000,000 trees, scientists placed the vast majority (1.39 trillion) in tropical and sub-tropical zones, 0.61 trillion in temperate regions and 0.74 trillion in boreal forests.

Boreal forests – the great band of conifers that circles the globe just below the Arctic, “Earth’s Green Crown” – are where the greatest tree densities are encountered on our planet.

 

Human Influence

The influence of human beings on the number of trees on Earth is clear from the study.  An estimated 15 billion trees are removed every year, with perhaps only five billion being planted back.  This translates into a net loss is about one third of a percent of the current number of trees globally.

A humoristic cartoon of Easter Island Maui Sculptures. Two Easter Island Maui head sculptures reminisce: "I remember when this was all trees".
Prior to deforestation, Easter Island would have been a very lush region.  By the time it was “discovered” by Europeans in 1722, the isolated would-be subtropical island was a barren landscape with no trees. Source: sustnrs.com

Tree losses are often tied to timber supplies and land conversion for agricultural use, as the global human population grows.

A comparison with estimates of ancient forest covers suggest that humanity could have already removed almost three trillion trees since the last Ice Age, around 11,000 years ago.

As stated above, the previous estimate of trees in the World was 400 billion.  The new estimate is three trillion large trees, but it must be pointed out that there are so many margins of error in the study that the real number could be anything between two or even 10 times higher.

As more information becomes available, it will be interesting to refine the estimates and check that key processes shaping spatial variability in tree density have not been overlooked.