Trees: Seeing the wood and the trees

From the oxygen they exhale to the wildlife they support, trees are indispensible, as Nicholas Schoon, Environmental Correspondent, explains.

Trees are the largest and oldest of living things, dwarfing our human size and longevity - there are yews in Britain around 4,000 years old. Happily, trees greatly outnumber humans in crowded Great Britain. We take them largely for granted, and when we do appreciate them we are usually reflecting on aesthetic and spiritual qualities not easily expressed in words. How can you explain what is so special about a broadleaf wood in midsummer; the muffled sounds of tossing leaves and birdsong, earthy smells, dappled, shifting light and the way they all come together? Let's eschew the poetic and concentrate on some hard-headed reasons why trees are an indispensable thing.

Oxygen

We and all the other animals need oxygen to live, and it all comes from trees and other green plants. One large, mature tree pumps out sufficient oxygen for a whole human family. They also absorb the carbon dioxide gas which we exhale as a waste gas - and which would suffocate us if it reached too high a concentration.

Wood

As synthetic materials become more prevalent, we are starting to value things made from real wood increasingly. Timber and wood pulp remain hugely important commodities; this newspaper and supplement could not exist without it. Great Britain and Northern Ireland produces about nine million cubic metres of timber a year, and rising. But that is only a fifth of what the UK consumes, so we rely heavily on imports.

Fighting pollution

Conifers and broadleaf trees in leaf are known to absorb airborne dust and copious quantities of key air pollutants such as sulphur dioxide, oxides of nitrogen and ozone as they waft through the canopy. Growing trees also absorb some of the extra, heat-trapping carbon dioxide we are adding to the atmosphere as humanity burns more and more coal, oil and gas. In one year, 140 broadleaf trees absorb as much carbon dioxide as spews out of the exhaust of one car doing an average year's mileage. We can plant trees to reduce the global warming we are causing by our profligate use of fossil fuels, but we need an awful lot of them.

Energy

Trees can also substitute for fossil fuels. We can burn them in power stations, then absorb the carbon dioxide (CO2) their combustion produces back out of the atmosphere as we grow the more trees for fuel. That way, there is no net addition of CO2 to the atmosphere. Construction of one such wood burning power station in Britain is about to start. Government scientists estimate that if a quarter of Britain's farmland was devoted to growing wood fuel as rapidly as possible, using willow coppices, it could generate two thirds of UK electricity.

Wildlife

Our 35 native species of tree, and our various types of woodland, are a habitat for thousands of plant and animal species. There are more than 200 different insect species which are associated with just one tree, the oak. Particular birds, mammals, butterflies, grasses and other plants and fungi all need woodlands. The huge stag beetle, our second largest insect, is just one example.

Recreation

What would walking, our most important outdoor recreation, be without woods to stroll through? Even the suburbs of big cities provide fragments of woodland within a few minutes walk of millions of their citizens. Greater London, for instance, has almost four per cent of its area covered in trees, making it more wooded than rural Cambridgeshire, England's most treeless county. Woods are just as important to cyclists and horse riders. And while a dozen walkers makes the bleak beauty of a mountainside in a National Park look crowded, an equivalent area of woodland next to a city can absorb hundreds of people without them bothering or even noticing each other. But as more and more of our growing areas of woodland become privately owned, local and national government and communities must fight to maximise public access. Like it or not, in the countryside bloodsports and woods go hand in hand - many copses only exist to provide cover for foxes and game birds.

Urban regeneration

Trees make cities more civilised and bearable, softening the sharp outlines and grey colour of buildings, roads and pavements. Single trees and urban woodlands are now recognised as a key tool in regenerating cities, in creating desirable developments and in restoring large areas left blighted by bygone industry.