THE planet is a much less green and pleasant place than it was when human civilisation first began, according to new international research.
The latest findings suggest the number of trees growing across the globe has halved in the past 12,000 years and now stands at around three trillion.
Though the figure is as much as eight times higher than some previous estimates have suggested, the scientists behind the study are warning that 15 billion trees are currently being lost worldwide every year as a result of man’s activities.
Their research shows the rate of tree loss is highest in tropical regions, which are home to around 43 per cent of the world’s trees, but they say the scale and consistency of the effect across all forested ecosystems highlight how historical land-use decisions have shaped natural ecosystems on a global scale.
American researcher Thomas Crowther and his team, including scientists from the UK, used satellite imagery from across the globe to assess how the density of trees was related to local characteristics such as climate, vegetation, soil conditions and the impacts of human activity.
Using the information from 400,000 measured tree density estimates, they were able to quantify the number of trees in the various regions. The result is a global map showing there are 3.04 trillion trees currently on Earth – the equivalent of around 422 for each person.
The highest densities of trees are found in the sub-Arctic regions of Russia, Scandinavia and North America, but the largest forest areas are in the tropics.
A country-by-country breakdown reveals there are more than three billion trees in the UK, which amounts to a below-average 47 for every Briton.
The researchers claim detailed information on tree populations will help efforts to study global systems such as carbon storage, the changing climate and the distribution of species.
“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution,” said lead researcher Mr Crowther, a post-doctoral fellow at Yale’s School of Forestry and Environmental Studies.
“They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services.
“Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don’t know where to begin.”
However, he also admitted he was “certainly surprised” to find the new figure was in the trillions.
He added: “We have nearly halved the number of trees on the planet, and we have seen the impacts on climate and human health as a result.
“This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”
In the past few decades, global forests are estimated to have absorbed as much as 30 per cent of annual man-made greenhouse gas emissions, about the same amount as the oceans.
Because of their ability to absorb carbon dioxide from the atmosphere and store it in soil and living and dead biomass, trees are considered a key factor in combatting the effects of climate change.
The study reveals patterns in tree densities between different habitats and provides insights into the factors that may control the number of trees within a particular ecosystem.
The research was prompted by a request for baseline estimates of tree numbers from a United Nations youth initiative as a way of helping set targets for tree-planting initiatives.
Previous studies had put global tree numbers at 400 billion.