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The U.S. Forest Service is reconsidering policies that limit the size of trees that can be removed in the course of restoration treatments in dry forests of eastern Oregon. To evaluate the effects of diameter limits on the ability of managers to meet restoration objectives, we used an existing network of long-term research plots to summarize historical and contemporary structure and composition of mixed-conifer forests within a one million-ha study area in eastern Oregon. Then, we used a novel thinning simulation procedure to quantify the degree to which thinning using different diameter limits restored stands to historical conditions. Contemporary mixed-conifer forests within the study area are significantly denser, have more basal area, and have a greater proportion of shade-tolerant species than historical conditions. Our simulations of thinning under current policy that prohibits cutting of trees ≥53 cm show that a quarter of mixed-conifer stands cannot be restored to within the historical range of basal area or density. Those stands that could be restored to within historical basal area ranges still had a substantially higher component of shade-tolerant trees than historical stands. Permitting larger shade-tolerant trees to be removed allowed restoration of all or most of stands to within historical structural and compositional ranges. Forest conditions in the late 1800s may not necessarily provide the best template for management because climate and disturbance projections suggest that eastern Oregon forests will be less well suited to shade-tolerant species in the future. Adapting stands to future conditions will require robust monitoring of forest structural and compositional response to restoration treatments.

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National Forest works collaboratively with diverse stakeholders to accelerate the pace and scale of forest restoration. Both informal joint fact-finding, empirical research, and multi-party monitoring are used to inform planning and adjust implementation of restoration treatments in an adaptive management framework. Knowledge of historical dynamics is often used to guide restoration on the Malheur because scientists, managers, and stakeholders believe restoring forest structure and composition to the historical range of variability will make forests more resilient to future climate and disturbance regimes. There is a strong shared understanding of the role of frequent, low-intensity fire in fostering resilience of dry, ponderosa pine dominated forests. However, there has been little empirical research describing historical disturbance dynamics in moister landscape settings. USDA Forest Service silviculturists and researchers from Oregon State University investigated historical fire patterns, forest structure, and composition in moist mixed conifer stands on the Malheur National Forest. The findings of this partnership demonstrate that moist mixed conifer forests historically experienced similar fire return intervals, had similar basal area, and in most cases are more departed from historical conditions than dry ponderosa pine forests. Tools were also developed to aid in selection of large-diameter, fire-intolerant species for removal. This research and ongoing fact-finding and dialogue with stakeholders have been used to adapt silvicultural prescriptions over time. A multi-party monitoring program is being implemented to answer stakeholder questions about the effects of restoration treatments, while generating baseline data to answer questions about intermediate and long-term environmental effects.

Reforestation in the Inland Northwest, including northeastern Oregon, USA, is often limited by a dry climate and soil moisture availability during the summer months. Reduction of competing vegetative cover in forest plantations is a common method for retaining available soil moisture. Several spring and summer site preparation (applied prior to planting) herbicide treatments were evaluated to determine their efficacy in reducing competing cover, thus retaining soil moisture, on three sites in northeastern Oregon. Results varied by site, year, and season of application. In general, sulfometuron (0.14 kg ai ha–1 alone and in various mixtures), imazapyr (0.42 ae kg ha–1), and hexazinone (1.68 kg ai ha–1) resulted in 3 to 17% cover of forbs and grasses in the first-year when applied in spring. Sulfometuron+glyphosate (2.2 kg ha–1) consistently reduced grasses and forbs for the first year when applied in summer, but forbs recovered in the second year on two of three sites. Aminopyralid (0.12 kg ae ha–1)+sulfometuron applied in summer also led to comparable control of forb cover. In the second year after treatment, forb cover in treated plots was similar to levels in nontreated plots, and some species of forbs had increased relative to nontreated plots. Imazapyr (0.21 and 0.42 kg ha–1) at either rate, spring or summer 2007, or at lower rate (0.14 kg ha–1) with glyphosate in summer, provided the best control of shrubs, of which snowberry was the dominant species. Total vegetative cover was similar across all treatments seven and eight years after application, and differences in vegetation were related to site rather than treatment. In the first year after treatment, rates of soil moisture depletion in the 0- to 23-cm depth were correlated with vegetative cover, particularly late season soil moisture, suggesting increased water availability for tree seedling growth.