Experts say crowded trees lead to more stress and competition for water. It also increases the danger of destructive fires.
However, in the cooperative study, experts found that accelerating the thinning of forests would increase the amount of water reaching the Verde River and Salt River watersheds, which are vital for residents in the Phoenix metropolitan area and communities to the north.
Rob Marshall, director of the Nature Conservancy Center for Science and Public Policy in Arizona, said proper forest management is vital to nature and people.
"Especially in Northern Arizona, the forests are important to the local economies, they’re important to wildlife habitat and they’re important for water supplies for the small towns, as well as the cities in the Phoenix valley," Marshall said.
"So the forests...our livelihoods...our economy and our water supplies are inextricably linked together," he said.
He said Arizona agencies and other groups are planning to thin more than 300,000 forest acres over the next 10 years under the Four Forest Restoration Initiative.
For a copy of the cooperative study published in the online journal Public Library of Science, click here.