Thursday, May 19, 2022

More Species, but fewer Trees

There are an estimated three trillion trees in the world (although it is thought that there were twice as many at the dawn of civilisation). To help you picture this mind-boggling number, imagine a very large square of woodland measuring 1000 trees long by 1000 trees wide, containing one million trees. If all of the world’s trees were arranged in this way there would be three million such woodlands spread across the globe. Writing in Entangled Life, Merlin Sheldrake estimates that wood accounts for about 60% of the total mass of every living organism on Earth, amounting to some 300 gigatonnes of carbon. This is why trees are such an important ‘carbon sink’, storing carbon that would otherwise be present in the atmosphere as carbon dioxide (CO2) and helping to mitigate global warming. During the Carboniferous geologic period between 360 and 300 million years ago trees took so much CO2 from the atmosphere that Earth’s climate changed from hot and humid to cool and arid, resulting in the Carboniferous Rainforest Collapse. As vegetable matter from the rainforests decayed enormous quantities of peat formed, which later converted into the coal deposits that humans have been busy burning over the last few hundred years, releasing much of the stored carbon back into the atmosphere.

Not all trees are to be found in woodland, of course, but forests as defined by the United Nations Food and Agriculture Organization cover an estimated 40.6 million square kilometres (40.6m km2) or approximately 31% of the world’s land area, making forest the predominant terrestrial ecosystem on Earth. About half of the world’s forests are to be found in the five biggest countries (Russia, Canada, Brazil, USA and China), but the greatest density of trees is to be found in Finland, Sweden and Slovenia, each with around 70,000 trees per square kilometre. By comparison, just 13% of the UK’s total land area has tree cover (compared to an EU average of 35%). In an attempt to address this, the National Forest of England, an area of 200 square miles (520 km2) comprising parts of Leicestershire, Derbyshire and Staffordshire, has been planted with 8.5 million trees to add to the existing ancient woodland, and there are plans to create a Northern Forest with the aim of planting 50 million trees by 2032. Despite these and other tree-planting initiatives (about 7 billion trees were planted worldwide in 2019 alone) there is a net loss of about 10 billion trees each year, equivalent to 10,000 of our ‘one million tree woodlands’, and a study by the Center for Global Development predicted that the world will lose more than one million square miles (2.59m km2) of woodland to deforestation by 2050.

With so many trees it’s hard to believe that nearly one-third of the world’s tree species face extinction in the wild, although a recent study suggests that there are 14% more tree species than previously thought, bringing the estimated total number of species to 73,300, of which 9,200 are yet to be discovered. This raises the depressing prospect some tree species will disappear before we even know of their existence! The biggest threats to trees globally are forest clearance for growing crops, much of which is then fed to animals (affecting 29% of species), logging (27%), livestock farming (14%), development (13%) and fire (13%).

Sources and suggested reading:

Entangled Life by Merlin Sheldrake (Random House, 2021)

How many trees are in the world

One in three trees face extinction in wild, says new report

Earth has more tree species than we thought

and various pages of Wikipedia.

Around the World in 80 Trees by Jonathan Drori (Laurence King, 2020), beautifully illustrated by Lucille Clerc, is a fascinating and informative introduction to the world’s iconic tree species.

Paul Appleby is a Fellow of the UK Vegetarian Society and a former trustee of the Society and the UK Vegan Society.  He was secretary of Oxford Vegetarians (the forerunner of OxVeg) for 25 years from 1983 to 2008.  Until he retired in 2020, Paul was a Senior Statistician at the Cancer Epidemiology Unit, University of Oxford, working mainly on long-term studies of the health of vegetarians and vegans, including the EPIC-Oxford study.

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