Again.

A few years ago, Todd Palmer, an ecologist at the University of Florida, was walking past a fenced-off research site in Kenya when he noticed something curious: instead of thriving, acacia trees protected from leaf-eating elephants and giraffes were withering and dying. . .

The acacias and a species of ant that colonize them live together in an arrangement ecologists call mutualism. The ants nest in the trees’ bulbous thorns and sip on their nectar; in return, they swarm out ferociously, ready to bite, when a tree is disturbed by an elephant, a giraffe or other grazing animal.

But somehow, Dr. Palmer said, the trees seem to sense when no one is munching on their leaves and, after a year or so, seemingly decide “we are going to reduce our investment in ants” by not producing so many roomy thorns or so much tasty nectar. The ants’ responses to depleted nectar and nesting sites — lassitude is one — eventually encourage wood-boring beetles to invade the trees. Pretty soon their tunnels leave the trees spindly, sickly, dying or dead.

I'm surprised that this is news. It has been known for a long time that exclosures ruin environments. It seems that only ecologists, biologists and such are unaware of this. See this old post, Butterfly Effect, from an alternate universe that tells about yet another stupid Paul Ehrlich trick where he drove the bay checkerspot butterfly to extinction by closing its range to people and grazing animals. That, in turn, destroyed butterfly habitat. And see Native Humans, which mentions the infamous Drake exclosure:

The absurdity became painful to Dagget as he began to study places where "no use" (read: no ecological disturbance) intersected with declining land health, such as the famous Drake Exclosure, in central Arizona, which had been excluded from livestock use for forty years. The land inside the fence had become a biological wasteland . . .

Also see Ecology of Fear, which expands on this Aldo Leopold quote: "I have lived to see state after state extirpate its wolves. I have seen every edible bush and seedling browsed, first to anemic desuetude, and then to death."

One of the common stories in my region is of some woefully ignorant urban escapee who buys up land and promptly closes it to all use, especially grazing. Their heads are full of environmentalist mush about "slow elk", the bane of the environment. Their lands then degrade monotonically until they finally realize that they have no idea what they are doing and that some sort of balance is needed.

It will be some time still before the experts twig to these realities.