Thinning alternatives for ponderosa pine: tools and strategies for family forest owners

Density management of ponderosa pine (Pinus ponderosa) forests is critical for control of beetles, reducing risk of wildfire and capturing monetary, aesthetic, and ecological values. This case study examined periodic growth response of ponderosa pine 5 and 13 years after installation of a trial including three thinning regimes and an unthinned option in the Wallowa Mountains of northeast Oregon. Family forest owners and their advisors whose management goals include reducing fire and beetle risk and producing timber value can use the results of this case study with the stand density index (SDI) to evaluate thinning options. We analyzed mean tree diameter growth and periodic board foot volume growth of 8-in. diameter and larger trees for the four treatments applied to 85-100-year-old stands. Our treatments were used as a local test for SDI management guidelines and forest vegetation simulator (FVS). As expected, significant increases (alpha = 0.05) were found after 13 years in mean diameter growth of trees and periodic board foot volume growth per tree in the wide and free treatments compared to narrow and control. Thinning to 80 ft2 of basal area or the lower management zone SDI in previously unmanaged, 85-year-old ponderosa pine stands provided for faster tree growth, lower risk of mortality from mountain pine beetle (Dendroctonus ponderosae), and no appreciable sacrifice in value of stand growth. Total wood fiber production was better for narrow and control, but with greatly increased fire and beetle risk. This work substantiates research results that thinning to carefully prescribed stocking levels can increase volume growth per tree (even free selection) and maintain reasonable stand value growth even though cubic volume growth is diminished. The resulting changes in stand structure and reduced beetle and fire threats improve the odds that family forestland will generate their full potential of monetary and ecological benefits.