The severity of insect-caused tree mortality has increased in recent years throughout the West, and the insects have spread to previously unaffected plant communities. Several native bark beetle species in the Scolytidae family are altering extensive areas within Greater Yellowstone. Their feeding activity can girdle a tree in one summer, turning the crown red by the following summer and the needles usually drop within the next year, leaving a standing dead tree. Pockets of red-needled trees are evident throughout the park. Forest structure, tree health, and climate are the major factors in determining whether an outbreak expands; drought and warmer temperatures can make forests more vulnerable to infestation.

Updated 8/28/08