Planet’s total tree cover down 46% since arrival of humans

The Earth fairly bristles with trees, with new research showing it has an estimated 3.04 trillion of them.

Although this is almost 10 times more than expected, equating to 422 trees for every man, woman and child on the planet, the total has plummeted from 5.6 trillion trees - a 46 per cent fall - since the dawn of human civilisation.

No other factor has had such a profound impact on the world’s stock of trees.

Human activity, including deforestation for agriculture, land-use change and forest “asset stripping”, carries away away more than 15 billion trees a year.

The planting of about five billion trees helps offset this, but the research study led by Dr Tom Crowther of Yale University puts global forest cover loss at about 190,000 sq km each year.

Youth initiative

Details of the research are published on Wednesday in the journal Nature. Dr Crowther was asked to conduct the study after an approach by Plant for the Planet, a youth initiative that leads the UN Environmental Programme's Billion Tree Campaign, an effort to ensure the planting of a billion trees.

“This seemed like a reasonable goal,” Dr Crowther said, but people still needed baseline figures.

At the time the planet was estimated to have about 400 billion trees, but the study showed the Earth has a multiple of that amount. “They have remade their goal and will attempt to plant a trillion trees,” Dr Crowther said.

The study combined satellite data with almost 430,000 ground-sourced measurements of tree density to establish its estimates. The data also allowed them to provide a country-by-country guide to the most forested places on Earth.

The largest share of trees, almost 1.4 trillion, are found in tropical and subtropical forests, while 740 billion trees are in boreal regions in the far north. Another 610 billion are in temperate regions around the world.

The research provides total tree numbers per country, along with per square kilometre averages and per head of population.

Sweden has the most trees per square kilometre at 69,161, with Brunei second at 62,333. Ireland has 10,088 trees per square kilometre. If measured as trees per head of population, Sweden has 3,200, Brunei 856 and Ireland 154.

Forest cover

Ireland has the lowest level of forest cover in Europe, at 11 per cent, compared to a European average of 20 per cent, said Pat Neville of Coillte, the State forestry company.

The Department of Agriculture oversees policy on forestation, and the current 2016-2022 forestry programme calls for 5-6,000 hectares of new forest cover and a similar amount in reforestation of cut forest, he said.

Trees carry out a range of important functions, including locking up huge amounts of carbon, supporting water and air quality, and providing food and timber. They also produce vast amounts of oxygen and are hotbeds of genetic diversity. They are an essential part of the planet’s environment.

It is therefore frightening that humans are clearing off a net 10 billion trees a year. If unchecked, that rate would see a whole planet clear-out of trees within 300 years, with human activity the cause.