Trouble in pinon country

American Forests, Wntr, 2005 by William M. Ciesla

Large numbers of pinon pines are dying in the pinon-juniper forests of the Southwest due to a bark beetle outbreak triggered by several years of severe drought.

Covering portions of Arizona, California, Colorado, New Mexico, Nevada, and west Texas, the pinon-juniper forest is the West's largest forest ecosystem. These open woodlands provide habitat for birds, small mammals, and mule deer and are the dominant vegetation in many of the region's national parks and monuments, including Arches, Colorado National Monument, Cedar Breaks, Mesa Verde, and Grand Canyon. Pinon nuts were a staple in the diet of indigenous people of the Southwest and today are an ingredient in many regional dishes.

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Blamed for the damage is the pinon engraver beetle, Ips confuses, a Southwest native and an integral part of the pinon-juniper ecosystem. The beetles bore holes in the trees and lay their eggs; the larvae feed on the tree for several weeks before emerging fully grown to attack new trees. This process can be repeated from two to five times a year.

Symptoms of attack include reddish boring dust and pitch tubes on the bark surface. If the insects have completed their life cycle, the bark will be peppered with tiny round exit holes. Infested trees do not recover.

The current outbreak began in 2001 and continues. To date the most severe damage has occurred in the Four Corners region, especially in the vicinity of Cortez and Durango in Colorado and in portions of Arizona and New Mexico. The large number of dead pines pose a fire hazard, especially in residential areas established in pinon-juniper woodlands.

The current outbreak raises an interesting question. We know that the Anasazi, who built the cliff dwellings of Mesa Verde, Chaco Canyon, and other sites in the Southwest, disappeared sometime during the 13th century. One of the factors that may have contributed to the collapse of this culture was a long-term drought. Did that drought also trigger an outbreak of pinon engraver beetle, which destroyed a critical food source?