Managing Ponderosa Pine Forests in Central Oregon: Who Will Speak for the Soil?

The soils of the central Oregon pumice plateau are relatively young and infertile, yet support an array of plant diversity and growth in the region’s pine forests. Whether these coarsetextured, pumice and ash soils are resilient to forest disturbance is not well understood. We present results from a long-term experiment that examined changes in soil quality in response to combinations of thinning and repeated prescribed fire. Soil quality was generally unaffected in fifteen years following pre-commercial thinning. The soils were also resilient to fire with the exception of the loss of nearly 25 percent of the ecosystem’s total nitrogen due to burning in 1991 and 2002. Natural replacement of N by N-fixing shrubs such as snowbrush ceanothus (Ceanothus velutinus Dougl. ex Hook.) and antelope bitterbrush (Purshia tridentata (Pursh.) DC.) is an important means to offset N losses, along with careful planning of burn prescriptions to limit forest floor N consumption.