The kaya forests are a working demonstration of something conservation science arrived at late: that religious prohibition can be a more effective protection than law, and that it fails in a particular way when it fails.
What a kaya is. When the nine Mijikenda peoples moved into the Kenyan coastal hinterland, each established a kaya: a cleared, palisaded settlement in dense forest, sited defensively, with the forest itself left standing as concealment and protection. By the mid-twentieth century people had moved out to farm and trade, and the kaya ceased to be places of residence.
They did not cease to be sacred. The cleared site remains a place of prayer, of burial for elders, and of the deposit of fingo, protective talismans understood to safeguard the community. Authority rests with councils of elders, who control access, and the traditional rules are specific and restrictive: no cutting of trees, no grazing, no removal of wood or plants, no entry without permission, and certain groves and paths closed altogether. Entry has customarily required proper dress and observance.
The consequence is ecological. Those prohibitions preserved patches of East African coastal forest, a habitat that has been almost entirely cleared elsewhere along this coast, complete with endemic plant species surviving nowhere else. The forests exist because they were forbidden, not because anyone set out to conserve them.
The failure mode. Customary protection depends on the authority of those who enforce it, and that authority has been eroding: younger generations have moved away, converted, or ceased to accept elder jurisdiction, while land pressure on the coast has intensified. The forests have been cut into for building, for sand and titanium mining, and through the sale of land whose customary status the Kenyan state did not formally recognise, because customary sacred tenure has no straightforward standing in a registered land system. When the elders' word stops being sufficient, there is often nothing legal underneath it.
Kenya began gazetting kaya as national monuments in the early 1990s, giving statutory backing to what custom had held, and eleven were inscribed on the UNESCO World Heritage list in 2008.
There is a quiet cost in how this was achieved. The forests became defensible in public argument largely on biodiversity grounds, because that is the language planning systems and international bodies operate in. The sacred claim, which is the actual reason the trees are standing, has tended to travel as a supporting detail attached to the ecological case rather than as the case itself.