Montana ? Facing the combined pressures of climate change, hunters and lax protections, 600 grizzly bears in and around Yellowstone National Park are going back on the threatened species list under a federal court order issued Monday.

The ruling highlighted climate change’s devastation to whitebark pine forests, which produce nuts that some grizzlies rely upon as a mainstay.

With hundreds of thousands of the trees dead or dying over the last two decades, bears striking out in search of new food sources increasingly are being shot in conflicts with humans.

“There is a connection between whitebark pine and grizzly survival,” U.S. District Judge Donald Molloy wrote in Monday’s ruling.

Hunting for grizzlies is illegal. But at least 20 were killed last year by hunters acting in self-defense or after mistaking them for other animals.

The greater Yellowstone area of Montana, Idaho and Wyoming has one of the densest concentrations of grizzlies in the lower 48 states. The animals were declared recovered in March 2007 after bouncing back from near-extermination last century.