JACKSON, Wyo. (AP) — A report says Yellowstone National Park's air quality is worsening.

The Natural Resource Vital Signs report measures park health based on the condition of 25 natural resources in 2010. It was authored by Yellowstone National Park.

Temperature, precipitation, snowpack and streamflow are all within normal ranges.

But the Jackson Hole News & Guide reports (http://bit.ly/uT2fp4) that the study finds indications that the growing season in the park has been starting earlier and getting longer.

Biologists say the longer summer season allows pine beetles to reproduce more than once, and warmer temperatures mean fewer deep freezes to kill them. Many whitebark pine trees have died from beetles and blister rust.

It says visibility, ozone and sulfur concentrations are considered moderate worries, while nitrogen concentrations are a bigger concern.