The influence of underlying factors on treatment effectiveness of piñon-juniper removal in restoring sagebrush habitat

Background/Question/Methods

Due to numerous anthropogenic factors, piñon-juniper woodlands in the western U.S. are expanding into adjacent ecosystems, increasing fuel loads and decreasing wildlife habitat and native plant cover. Across the western U.S. natural resource managers are completing land treatments to remove piñon-juniper trees encroaching into sagebrush habitats. We assessed land treatments that have been completed across northwest Colorado with the goals of improving wildlife habitat, improving rangelands, and reducing fuels. Our aim was to evaluate the influence of underlying ecological and management factors on treatment effectiveness. Using a combination of traditional monitoring methods (line-point intercept, species inventory, vegetation height), as well as an uncrewed aerial vehicle (UAV), we collected species composition and plot recovery data. Percent sagebrush cover, percent perennial forb and grass cover, percent invasive species cover, and vegetation height were collected to assess plant community recovery. A UAV flew a systematic path over each plot collecting aerial images, allowing us to incorporate landscape-level data with plot-level data. The underlying factors we considered in plant community responses to a range of tree removal strategies (e.g. mastication, prescribed burning, hand removal) were treatment method, treatment age, management history, elevation, slope, aspect, mean annual precipitation, temperature, and soil temperature and moisture class.

Results/Conclusions

We found that elevation, mean annual precipitation, and treatment type had the greatest impact on treatment effectiveness. Sites at higher elevations were associated with cooler, wetter climates which supported a higher percent cover of forbs and grasses. Of the various treatment methods, mastication treatment sites had the highest percent cover of litter, creating suitable microclimates for forb and grass germination and therefore improving percent cover of forbs and grasses. Treatment sites that had been burned (either by prescribed burning or wildfire) had increased cover of invasive species. Invasive species cover was also found to be high in sites with a history of recreation and in sites closer to heavily-trafficked roads. With these data, recommendations can be made to support land managers in the planning process for future piñon-juniper treatments to enhance treatment efficiency and effectiveness.