Yellowstone's wolves teach us nature knows best

Wolves, as you have undoubtedly heard, are once again thriving in Yellowstone. The 66 trapped in Canada and released in Yellowstone and the Idaho wilderness in 1995-96 have generated more than 1,700 wolves. To the delight of scientists and tourists — and the dismay of many ranchers — more than 200 wolf packs exist in the area today. Courts and government agencies are still sorting out how the wolves should be managed. But one thing is abundantly clear: The reintroduction has succeeded in ways that extend far beyond the health of the wolves themselves. It has reshaped an entire ecosystem.

When we exterminated wolves from Yellowstone in the early 1900s, we de-watered the land. That's right; no wolves eventually meant fewer streams, creeks, marshes and springs across Western landscapes like Yellowstone where wolves had once thrived.

The chain of effects went roughly like this: No wolves meant that many more elk crowded onto inviting river and stream banks. A growing population of fat elk, in no danger of being turned into prey, gnawed down willow and aspen seedlings before they could mature. As the willows declined, so did beavers, which used the trees for food and building material. When beavers build dams and make ponds, they create wetland habitats for countless bugs, amphibians, fish, birds and plants, as well as slowing the flow of water and distributing it over broad areas. The consequences of their decline rippled across the land.

Meanwhile, as the land dried up, Yellowstone's overgrazed riverbanks eroded. Spawning beds for fish silted over. Amphibians lost precious shade. Yellowstone's web of life was fraying.

The decision to put wolves back in Yellowstone was a bold experiment backed by the best conservation science available to restore a cherished American ecosystem that was coming apart at the seams.

The unexpected relationship between absent wolves and absent water is just one example of how large predators such as grizzlies, wolves and mountain lions regulate their ecosystems from the top down. The results are especially relevant in an era of historic droughts and global warming, both of which are stressing already arid Western lands.