Who doesn't like a good nature story. It sounds like the wolves are doing more to restore the ecosystem than expected.
For the past 15 years, the leader of the Gray Wolf Restoration Project Dr Doug Smith and his team have monitored the effects of wolves on Yellowstone.
Thirty-one of the animals were released in 1995 and 1996, and Dr Smith now puts the number at about 100.
Their research suggested that predators not only influence the numbers of plant-eating animals through predation but through a complex series of interactions in the ecosystem, the predators can also restore forests.
Dr Smith has noticed dramatic changes amongst the willow stands that grow in Yellowstone's river valleys.
He said: "When I first came to Yellowstone about 16 years ago the willows here were all eaten by elk.
"But since wolves have been reintroduced we saw the willow come back, before our eyes. A big factor is, very simply, wolves eat elk, so it's connected."
The absence of wolves between 1926 and 1995 coincided with a loss of beaver populations in the park, but since the wolves returned, beavers have been drawn back by the increase in willow.
Now that the beavers are back and building dams, the water table in areas of the park that were suffering from deforestation has begun to rise, restoring populations of water hungry species of tree like willow and aspen.
"The missing piece of the puzzle was the wolf, the top predator," Dr Smith said.
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