Assessing Piñon Pine Mortality

Piñon pine mortality.

Beginning around 2002, extensive piñon pine (especially Pinus edulis and P. monophylla) mortality appeared throughout the Western United States. Dense stocking and sustained drought weakened the defenses of the pines, making them highly susceptible to attack by piñon ips bark beetles (Ips confusus (LeConte)) and other insects, as well as infection by black stain root disease (Leptographium wageneri (Kendrick) Wingfield) and other disease agents. Insect feeding and diseases destroy and clog the conductive tissues of the trees, causing them to die. The piñon ips beetle, the most important mortality-causing agent of the recent mortality event, is a native species that typically plays an important role in maintaining healthy forests by removing stressed or injured trees. This process thins the forest and reduces competition for water, nutrients, and light. Healthy trees are generally unaffected by the beetles. However, the abundance of drought-weakened trees allowed beetle populations to explode, causing extensive mortality in stressed and healthy trees throughout the piñon/juniper range (Figure on the right) (Keyes and Hebertson 2003, Negron and Wilson 2003, Shaw and others 2005).

Because piñon/juniper woodlands are not routinely monitored, assessing the ecological impact of the mortality and the fire hazard it presented became very difficult. Therefore, a rapid and cost-effective multistage sample design incorporating digital aerial imagery was developed to assess tree mortality.