Untidy, I thought when I approached the board walk alongside the Coy Burn near Crathes Castle. Branches and twigs had sprawled into the water, bobbing on the rhythms of the babbling stream. As people squeezed passed on the planked path I took it in. A tree had fallen across the stream and branches, twigs and leaves had become entangled in it. A pile of more or less equally long branches had become heaped up on the upstream side of the trunk as if someone had accidentally dropped an armful of firewood in the water. Something in this tangle moved. I probably noticed it because the movement was not caused by the bobbing burn. Then I saw it: a wren, its tail cocked up, on twigs low above the water. I should not have been surprised, this tangle, full invertebrates, must provide a healthy meal on a chilly winter day.
The tree had probably fallen over the stream by itself, uprooted when the Coy Burn was in full spate or just because it was old. I wondered which invertebrates live in those heaps of wet leaves in the river. Who would they be eaten by? Would fish find shelter in this tangle? Further downstream I had looked at the ladder installed to help salmon negotiate the dam and enter the Mill Pond ten years ago. Could it be, perhaps … would it be too much to ask for a salmon to find shelter in the vicinity of this fallen tree? After some rain recently the burn is muddy, and there is no way to tell.
As I walk on I notice more trees and branches in the water and every time smaller branches, twigs and leaves have piled up behind it. I looked around. This could be the work of beavers, but alas, beavers are still to reach Deeside. True, the ecological impact of fallen trees across small watercourses has similarities. The heaped up debris form these floating, temporary dams slows down the flow of water andmay even cause the river to exaggerate or create new meanders. All that is needed is one tree to fall across the water, and the knock-one effects will seep through the burn and bank ecosystem over time. Tidy streams are all but natural.
In the project Water / Shed I will investigate the ecology of water in its manifestations in the catchment of the river Dee and the options we have to manage these water resources in a sustainable way.
Copyright text and images Petra Vergunst