Trees are key to biodiversity – Abingdon Herald

By John Killick, written for the Abingdon Herald, 15 June 2023

I wrote last time that forests host 80% of land-based species, so I have more to say about trees.

For millennia people thought that trees grew by taking in soil. In 1634 a Flemish chemist Jan van Helmont put a willow sapling in a big pot and let it grow for 5 years. He weighed the tree and the soil before and after; the tree had added 164 pounds. The soil weight had hardly changed, so where had the tree come from?

It wasn’t till 1808 that a Swiss scientist Nicolas de Saussure concluded that the tree’s main source of food was carbon dioxide in the air.

Birches were among the first trees to colonise Britain after the Ice Age and quickly exploit ground cleared by people, so now comprise a fifth of Britain’s forests. Most trees can produce habitats for many other species; one survey found that birch supports 229 kinds of insect and its acid bark has 126 lichens and many mosses. Twenty common toadstools collaborate with birch roots, including our favourite (but toxic) red fly-agaric.

In general, the longer a tree species has been in Britain, the more insects and other creatures have adapted to it. This means that when we are planting trees it is better to plant native ones.

But many alien species are attractive in their own right and some have unexpected benefits. The Wellingtonia and Monkey Puzzle in Albert Park are declining in their respective natural homes, California and Chile, but it seems that after 300 million years confined to the Southern hemisphere Monkey Puzzles, imported to Europe 200 years ago, are doing better here.

However, care is vital when we import trees. In the 1960s elms were abundant and handsome in most of Britain. Then Rock Elm was imported from Canada; it had a virulent strain of Dutch Elm disease, which invaded our elms and perhaps 25 million of them died and were felled in a few years. Their huge amount of carbon is adding to climate change.

Crucial to the survival of biodiversity and also to our maintaining a reasonable climate is, of course, the survival of the Amazon rainforest. It has lasted 55 million years and until recently supported one tenth of the world’s land-based species; it extends far outside Brazil and its 5.5 million square kilometres is forty times the size of England. Sadly about 18 percent of it has been lost by 2019.

It is threatened by logging and clearance for local farming, soya beans and cattle, and after trees are cleared, the soil gets poorer and rainfall less.

This autumn, Abingdon Carbon Cutters will have another tree planting event, so look out for news on that to get involved.

Alternatively, choose three trees for free in the ‘Oxfrordshire Garden Tree Giveaway.’ Trees will be available in Autumn 2023, with more info available here.