Black Stain Root Disease Studies on Ponderosa Pine - Parameters and Disturbance Treatments Affecting Infection and Mortality

Black stain root disease of ponderosa pine (Pinus ponderosa Doug. Ex Laws.), caused by Leptographium wageneri var. ponderosum (Harrington & Cobb) Harrington & Cobb, is increasing on many eastside Sierra Nevada pine stands in northeastern California. The disease is spread from tree to tree via root contacts and grafts but overland spread of the disease is most likely due to woody root feeding bark beetle (Coleoptera:Scolytidae) vectors. Soil and site relations along with disturbance are factors in the etiology of the disease (Harrington and Cobb 1988). Thinning and prescribed burning are important silvicultural tools in maintaining forest health in eastside pine stands. Because soil compaction is a concern in many sites, skid trails are treated by subsoiling equipment to alleviate compaction where this might be an issue. However, little is known of the effects of these silvicultural treatments on incidence of black stain root disease on sites with high disease risk. Because the woody root feeding insects that vector the disease respond to disturbance (Otrosina – Ferrell 1995), understanding consequences of different disturbances resulting from silvicultural treatments is essential for devising management plans to mitigate disease impact This paper summarizes preliminary results from two long-term studies initiated in 1996 and 2000 to address these issues.