Earth Day – make that Soil Day

April 22nd is Earth Day. Events are going on all over the world; and the Earth Day website has a map showing where the nearest events to you are.

The irony of having a single day in the year when the wellbeing of the whole planet is celebrated is not lost on us at Woods for the Trees. Even so, we have been asking ourselves how to mark it. It’s a lousy time of year for planting trees (at least in the Northern hemisphere); and it has no particular cosmic significance (part way between the Spring equinox and the Summer Solstice); but in an Environmental calendar full of reminders to get out there and do something for nature, or use less plastic, or stop flying, there’s something to be said for thinking about the earth. And, as an archaeologist, when I think of earth I mean soil: the fine particles of rock ground down by weathering and accumulated by erosion, graded into sand, silt and clay by rivers and lakes, and left around much of the planet conveniently as a medium for plants to grow.

All the soils I have ever dug in – from the Thames clays and Cheviot brown earths to the caliche of the American South-west desert, have had a human component: soils are artefacts as much as they are ‘nature’. And just as ancient woodlands are social ecologies – partnerships between nature and sustained human management – so soils, much less visible but so important for planetary health – are the accumulated record of that relationship: what archaeologists call the stratigraphy.

What gardeners think of as good quality topsoil combines silt, sand and clay in more or less equal proportions (a ‘loam’), with decayed vegetable matter to create a rich growing medium full of nutrients. Moles, earthworms (a favourite subject of Charles Darwin, who devoted his last book to their study) and other invertebrates aerate and process the soil and its vegetable matter, turning it into a fine tilth. Plants like legumes trap atmospheric nitrogen with root nodules to increase fertility. Tree roots combine with tiny filaments of mycorrhizal fungi to share sugars and trace minerals. Leaves, those miraculous but understated solar panels, fall, rot, and replenish. In woodland soils that have been stable, self-sustaining micro-habitats for hundreds or thousands of years, unique biomes of bugs, fungi and bacteria evolve.

You could cut down all the trees in an ancient wood (please don’t); but the soil would still be ancient woodland soil: complex, precious, full of carbon and very fragile. So far as I am aware, it is not known just how long a new woodland takes to acquire its own genuine woodland soil. My young trees still grow in what is former pasture and arable earth. I suspect that it’ll still be pasture soil for a while after I’m gone. But I watch each batch of autumn leaves falling and being consumed; make sure to leave trimmings and branches lying on the ground to rot – attracting, I hope, all those wood eating fungi and beetles that will process it; I let moles and worms do their thing. And every day, every passing year that the land has trees on it takes it a tiny step towards being something to celebrate, on another Earth Day, many years in the future.

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