PS 29-150 - Effectiveness monitoring for a sugar pine health improvement project on the Umpqua National Forest

Abstract: Maintaining sugar pine (Pinus lambertiana) on the landscape is an important management goal for the Umpqua National Forest in southwest Oregon, USA. This charismatic tree species is relatively well-adapted to increasingly frequent drought and fire, but threatened by introduced white pine blister rust, endemic bark beetle outbreaks, and increased competition due to fire exclusion. Thinning competing trees has been proposed to reduce stress on large, old sugar pines and improve seedling recruitment, but a previous study found that mature pine survival was not significantly improved over 16 years by removing competing trees within 1.5-2.5 times the crown radius of individual pines, although seedlings were more likely to be present around trees that received more thinning. On the Umpqua National Forest, a new landscape resilience project is underway to combine “radial thinning” with stand-level thinning of different intensities, and to monitor the effects on health and survival of sugar pines and their regeneration.

In 2021-2022, we collected baseline health data on 538 individual adult sugar pines within stands scheduled to receive one of four treatments: 1) radial thinning of non-pine conifers < 61 cm diameter within approximately twice the pine’s crown radius, plus felling of non-pine conifers < 18 cm throughout the stand; 2) the same radial thinning plus timber harvest of non-pine conifers < 51 cm, leaving a stand basal area of 28-73 m2/ha; 3) radial thinning around roadside pines; and 4) no treatment. We also quantified regeneration of sugar pine and other species and competitive environment around 66 of the mature pines. Prior to treatment, 59% of the measured pines were missing between 1/3 and 2/3 of possible foliage relative to a healthy symmetrical crown, and 26% had blister rust symptoms, with the highest proportion of symptoms (36%) in the control stands. Mountain pine beetle was not active in the project vicinity. Sugar pine regeneration occurred on 92% of plots and was positively associated with live sugar pine basal area and abundance of heterospecific regeneration, suggesting that so far, competition does not limit seedling abundance. Overall, environmental conditions and pine health metrics were similar across planned treatment types, despite designing the study around a preexisting project. The non-timber treatments were completed in fall 2022 and monitoring will resume when all treatments are completed, allowing ongoing measurement of whether these operational forest management practices benefit sugar pine.