Forest-thinning projects in Arizona and California have been put on hold amid concerns over the health and safety of endangered species in the forest.

In Flagstaff, Ariz., environmentalists are worried about the negative effects tree-thinning efforts might have on the endangered Mexican spotted owl and the prey it relies upon to survive. In California, wildlife advocates concerned about the well-being of the Sierra Nevada yellow-legged frog.

The Mexican spotted owl has been on the endangered species list for more than 30 years, while the Sierra Nevada yellow-legged frog was only just granted federal protection this past April.

Forest or tree thinning is the the act of taking down dead trees and removing smaller trees from a forest to prevent or curb the severity of wildfires. Forest officials have championed the practice as a way to proactively address the growing problem of fire in the West. But some conservationists say the practice is an excuse to let more loggers into protected forests.

Lawsuits in both Arizona and Utah are just two of many legal standoffs, pitting forest managers against environmental groups.

In California, the Forest Service's "Upper Echo Lakes Hazardous Fuels Reduction Project" is on hold as it awaits the resolution over two separate lawsuits. Plaintiffs in the suit say the thinning would unnecessarily harm the protected frog.

"At a minimum, the Forest Service should have conducted surveys of the project area to determine whether its activities would harm the species and its habitat," Dr. Dennis Murphy told the Tahoe Daily Tribute, "but instead the agency put on blinders to the impacts of the project hoping no one would notice."

Murphy is a Pew scholar in conservation and a plaintiff in one of the two suits.

A similar suit has slowed another thinning plan in Arizona. Proponents of the thinning plan say environmentalists are missing the big picture -- that forest thinning is good for the forest and thus good for the owl.

"The Schultz fire showed us the price of inaction, and the fact that the voters of Flagstaff are willing to spend $10 million on the Dry Lake Hills project shows that they want this problem addressed," Stephen Dewhurst, an associate professor in Northern Arizona University's School of Forestry, recently told the Arizona Daily Sun. "Over the long term, that's going to be good for the owl and for us too."