Profitable Wonders James Le Fanu
Trees – with their branches reaching upwards, their trunks rooted in the soil – connect the two domains of heaven and earth in a ceaseless cycle of biochemical transformations.
For millennia, the dense forests that covered a third (or more) of the land surface were the most essential, seemingly inexhaustible, of all natural resources.
They were the source of the fuel for the fires whose heat warmed our bygone ancestors, cooked their food, baked their bread and transmuted clay into pottery, sand into glass, and metals into tools, weapons and ornaments.
Trees were the source, too, of the materials for building their homes and public buildings, the furniture and artefacts with which they filled them and every conceivable mode of transport: carts, chariots, wagons, barges and ships.
‘Without this constant supply of wood felled from forests,’ notes the historian John Perlin, ‘the great civilisations of Sumer, Assyria, China, Mycenae, Greece and Rome, Western Europe and North America would never have emerged.’
Above and beyond these manifold favours, the greatest gift of trees is in making the Earth habitable. We start most obviously with the air we breathe, enriched with life-sustaining oxygen while simultaneously cleansed of those ‘greenhouse’ gases, notably carbon dioxide. This is the never-ending dance of photosynthesis. Moment by moment, the wondrous green pigment chlorophyll in the leaves captures the energy from the sun to split molecules of water into their constituent atoms, oxygen and hydrogen.
Every year, the 200,000 leaves of a mature oak release sufficient quantities of oxygen into the atmosphere to meet the needs of half a dozen people. Meanwhile, simultaneously, those same leaves are combining the remaining ‘free’ hydrogen with carbon dioxide absorbed from the air through minute apertures on their undersurface. Together, hydrogen and carbon form organic compounds that, through a series of chemical transformations, will become the tough cellulose and lignin laid down as the trees’ woody ‘new growth’ year on year.
The three trillion trees on the planet thus function as a massive carbon sink, removing prodigious amounts of carbon dioxide from circulation – 300 million tons a year in the United States – and storing it inaccessibly as the fabric of their trunks and branches. The relatively simple expedient of increasing the world’s forest cover by one third would, the journal Science claimed last year, offset the warming effects of a century’s worth of carbon emissions.
Paralleling this contribution to purifying the air, trees fulfil the equally crucial role of enriching and stabilising the soil. At its simplest, their discarded leaves and twigs – fed on by microbes, fungi, beetles and other minuscule creatures – are transformed into a rich, growth-generating, nitrogenous compost.
And the taller the trees grow, the more extensive the network of roots below the surface, binding the soil together and protecting it from being eroded by the harsh elements of rain and wind.
The major threat posed by a heavy storm is mitigated by another, less well-appreciated attribute of trees: preventing the ground from becoming saturated. A large tree shifts water on a major scale: 500 litres a day is sucked up from the ground and transpired out through its leaves. The presence of trees has a significant drying effect, limiting the run-off into rivers which are thus less likely to overrun their banks and flood the surrounding countryside.
Hence the ecologically catastrophic consequences of deforestation – first and most eloquently described by a Venetian, Giuseppe Paulini, in the 17th century. Over the preceding centuries, the demand for timber from the great shipyard at the Venice Arsenal had denuded the nearby mountains of their trees.
‘Since there is now no vegetation to retain rainwater,’ he wrote, ‘after a storm, water swoops precipitously down to devastate the countryside, bringing all the filthiest debris to the river’s mouth.’
The consequent silting-up of the lagoon, he warned, threatened the future commerce and security of the Republic.
The corollary – where reforestation restores the fertility and stability of the soil – is seen to most dramatic effect in the re-greening of the Sahel on the southern edge of the Sahara. Since the 1980s, a systematic programme of tree-planting – more than one million a year – has rehabilitated five million hectares of land, now producing an additional 500,000 tons of food a year.
There can be no more persuasive evidence of the indispensability of trees in uniting those two domains of heaven and earth.