What a forest remembers

Two patches of woodland can look identical and be entirely different things. One grew back on abandoned farmland forty years ago. The other has been continuously wooded for four hundred years. From a path they are both trees.

The difference is in the soil and in what moves slowly. Many woodland plants spread only a few metres per century; they have no mechanism for crossing a ploughed field. Certain mosses, fungal networks and ground flowers are therefore found almost exclusively in woodland that was never cleared, and ecologists use them as indicators. The presence of a particular small flower can mean that this ground has been shaded since before the village church was built.

This matters for policy in a way that is frequently missed. When a road is planned through ancient woodland, the standard mitigation is to plant replacement trees elsewhere, sometimes at generous ratios: five hectares planted for every hectare lost. The arithmetic is reassuring and the biology does not support it. Trees can be replaced in decades. The soil community beneath them cannot, because the organisms that build it arrive at a pace measured in centuries.

There is no good way to express this in a compensation agreement, which is part of why it keeps happening. A planting commitment is countable and can be written into a contract. 'Four hundred years of undisturbed soil' cannot be delivered by any party to any agreement, so it tends to fall out of the negotiation entirely.

What cannot be written into the deal is not thereby worth nothing. It is simply unprotected.