Effects of Fuel Management Treatments in Piñon Juniper Vegetation at a Site on the
Colorado Plateau

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A project funded by the Joint Fire Science Program

Woodlands dominated by piñon and juniper occupy over 30 million hecatares of the western United States. Prior to European settlement of this region during the late 1800s; the expansion of the piñon-juniper range may have only just begun, since it currently occupies less area then climate conditions seem to allow. Where woodlands are currently established, the type-conversion from shrubland to woodland continues as understory shrub, bunchgrass, and herbaceous species are slowly forced out as the overstory cover of woodland tree species closes in on them. This vegetation type-conversion leads to decreased species diversity, loss of soil seedbanks, decreased aquifer recharge, increased soil erosion, and increased chance of high intensity crown fires.

The range expansion of piñon juniper was associated with increased fire return intervals due partly to fire suppression and the reduction of surface fuels caused by the introduction of livestock grazing by European settlers. In an attempt to return stands to pre-settlement conditions dominated by sagebrush steppe and lower fire return intervals, and to improve livestock forage and wildlife habitat, land managers have attempted to reintroduce fire and manipulate fuel conditions using mechanical, chemical, seeding, and fire treatments.

Where woodlands are dense, fire does not propagate easily except under extreme fire weather conditions which typically results in intense crown fires that have undesirable effects on soils and plants. Where woodlands are more open and still possess surface fuels, managers can create low to moderate intensity surface fires with sporadic torching of larger trees, but even in these conditions fire can be hard to propagate. For these reasons, sites have often been prepped before burning, typically by chaining landscapes to uproot trees and provide opportunities for early successional forbs, grasses, and shrubs to re-establish. However, chaining results in removal of both pre- and post-settlement trees and creates significant soil disturbance, which is not compatible with the management goals of many land management agencies, especially the National Park Service. As a result, mechanical thinning or chemical treatment of post-settlement trees is becoming more common, since it creates uneven-aged woodland stands that are more natural and provide better wildlife habitat, and does not create significant soil disturbance. Minimizing soil disturbance is especially important in areas where cultural resources may otherwise be at risk. Follow-up seeding of grasses has also been used to help establish plant cover to minimize soil erosion, and to increase fine fuel loads that are necessary to help re-establish a low intensity surface fire regime.

Although there is some literature on the ecology and management of piñon-juniper woodlands, very little is known about the combined effects of thinning, seeding, and burning, and effects are likely variable across its extensive range extending from the Columbia plateau and Great Basin desert to the Colorado plateau in western North America. Possible differences across this geographic range include the presence of different species of piñon, juniper, and understory plant species, and differences in the ratio of summer:winter rainfall.