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 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