The otherworld had an address, and it was usually the field you did not plough

Across a wide range of traditions there are places that people do not use. A grove that is not cut. A mound that is not ploughed. A tree that is not felled. A spring approached only in a particular way. A hill nobody builds on.

The explanations given differ enormously. The behavioural result is consistent, and it has had measurable effects on landscapes.

Sacred groves

The best-documented case, because ecologists have studied them.

Sacred groves — patches of forest protected by religious or customary prohibition — are found across India, West Africa, Ethiopia, parts of East Asia and elsewhere. They range from a few trees to substantial areas.

Ecological surveys have repeatedly found that these patches hold higher biodiversity and older trees than surrounding land, and in heavily cleared regions they sometimes represent the only remaining fragments of original vegetation. In parts of Ethiopia, church forests are visible from the air as circles of green in otherwise cultivated land.

They also frequently protect water sources, which is not a coincidence: groves around springs are common, and the vegetation genuinely does regulate the water supply.

The mounds and the fields

In Ireland and parts of Britain and Scandinavia, prohibitions attached to particular earthworks, trees and mounds — many of them prehistoric monuments whose original function had long been forgotten.

The prohibition was framed in terms of the beings who lived there and what they would do if disturbed. Farmers ploughed around them. Lone hawthorns in the middle of fields were left standing. Building on certain ground was avoided.

The consequence is that a considerable number of prehistoric monuments survived to be excavated in the twentieth century because ploughing had gone round them for two thousand years.

There are documented modern instances of infrastructure projects being rerouted in response to such beliefs, which suggests the tradition has not entirely lapsed.

Reading it functionally, carefully

There is a tempting reading in which these beliefs are simply conservation encoded as religion, invented by wise ancestors who understood ecology.

That reading is too neat. People who protected sacred groves were not conducting conservation under a mythological cover story. They believed what they said they believed, and the ecological effect was a consequence rather than a purpose.

It is also not universally true that traditional practices were sustainable. There are well-documented cases of pre-industrial societies degrading their environments severely.

What can be said is narrower and still interesting: prohibitions framed as sacred are considerably more durable than prohibitions framed as policy. A rule that is enforced by fear of supernatural consequence does not require an inspector, survives changes of government, and is passed to children without an argument.

Other forms the same behaviour takes

Seasonal prohibitions. Not hunting a species at certain times, not fishing certain grounds in certain months, not cutting certain plants before a date. Where these coincide with breeding seasons — and they frequently do — the effect is a closed season.

Species prohibitions. Animals that particular groups do not kill or eat, often tied to clan identity. Where different clans have different prohibitions, the aggregate effect across a population is that a range of species have some protection.

Access restrictions. Places that only certain people may enter, or that require ritual preparation. Restricting access restricts use.

Where it breaks down

These systems depend on shared belief and on social enforcement. Both erode with religious change, migration, and the arrival of external authority that does not recognise customary rules.

The pattern across many regions has been that sacred groves survived until land tenure changed, or until a road made the timber accessible to someone outside the community, or until conversion made the prohibition meaningless to a new generation.

Conservation organisations have in several places attempted to work with customary protections rather than replacing them, on the reasoning that a rule people already follow is more effective than a new one they do not. Results vary and depend heavily on whether the community retains any actual control over the land.

The wider point

The interesting fact is not that traditional beliefs sometimes produce good ecological outcomes. It is that durable restraint on resource use is difficult to achieve by any means, and that societies which managed it generally did so by embedding the restraint in something other than a calculation.

A rule that says this ground is not for you, because of something older than you, and enforced by consequences you do not want to test, turns out to be a robust piece of social technology. Whatever else one thinks about it, it kept a lot of trees standing.