An Underwater Walk in a Beech Woodland

Easter holidays are here, take the chance to get out and about in a woodland near you. Tessa Wardley describes a recent trip:

I’m crouched down leaning against the smooth bark of an old Beech tree, it is a rare sunny day this winter and I’m hiding, as part of a game of ‘thicket’. I’m well hidden by the girth of the tree even in my layers of down jacket and I peer up to contemplate the canopy that reaches invitingly over my head. At this time of year there is little leaf cover but if I close my eyes I can imagine the light filtering down through the leaves, each one a tiny solar panel, carefully arranged to capture the maximum amount of light without stealing it from another leaf. The sensation of walking through a woodland in leaf is often compared to swimming in an underwater world.

As the weak, green light envelopes you, birds swim through the tree tops making shrieking dives through to the lower layers as if fish slicing through water. The clicks and creaks of underwater sounds are echoed by the activities of insects and small mammals in the trees and undergrowth, the rub of bark where branches overlap; and the ebb and flow of the wind in the leaves is very reminiscent of waves breaking on a sand and gravel shore

The quality of the attenuated light that filters through the leaves of a woodland canopy compares closely to the light that filters through the upper surface of water. In a mature beech wood just 5% of the incident light will reach down to the forest floor, the leaves filter out the long and short wavelengths of the blue and red ends of the spectrum for photosynthesis, leaving the mid length green light to dominate the light. Similarly when we are underwater the red and orange, long-wavelength, light is absorbed rapidly in the upper surface of the water leaving the greens and blues to penetrate more deeply and be absorbed more slowly. Biologically rich waters will also absorb the blue end of the spectrum, leaving again the green tinged experience reminiscent of the woodland walk.
My thoughts are wandering along in this vein when I am interrupted by the wet, black nose of our dog Alfie and my hiding place is rumbled – ‘Mum I can see you behind the tree!!