COS 296-2 - CANCELLED - Assessing the effectiveness of pinyon-juniper removal in restoring sagebrush habitat: a causal inference approach

Abstract: Pinyon-juniper woodlands in the western United States are expanding into adjacent ecosystems due to numerous anthropogenic factors. This expansion is increasing fuel loads and causing a decline in native plant cover, negatively impacting wildlife habitat and increasing wildfire risk. In order to combat this expansion, natural resource managers across the western U.S. are completing landscape-level treatments to remove pinyon pine and juniper trees that are encroaching into sagebrush habitats. In collaboration with land managers in Colorado, we assessed pinyon-juniper removal treatments that have been completed across northwest Colorado with the goals of improving wildlife habitat and reducing fuel loads. Using vegetation cover data from the Bureau of Land Management’s Assessment, Inventory, and Monitoring (AIM) program, we quantified percent sagebrush cover, percent native forb and grass cover, and percent invasive species cover in order to assess plant community recovery after tree removal. In our evaluation, we considered the influence of underlying factors such as management history, topography, climate, edaphic conditions, and ecological site, as well as the direct factors of tree removal strategy (e.g. mastication, prescribed burning, hand removal), treatment goal, and treatment age, on plant community response to treatments.

Using a causal inference approach, specifically matching methods, we assessed the average treatment effects of pinyon-juniper removal. We found that treatment type, management history, and elevation were all associated with plant community recovery after treatment. Tree removal method had varying impacts on vegetation cover post-treatment, with mastication sites having the highest litter cover, creating suitable microclimates for forb and grass germination, therefore improving percent cover of native forbs and grasses. Sites where broadcast burning was used for tree removal had limited vegetation recovery, likely due to enhanced soil erosion at these sites. Invasive species cover was highest at sites with a history of recreation and sites closer to heavily-trafficked roads, limiting recovery of native plant species. Higher elevation sites were associated with cooler, wetter climates which supported a high percent cover of native forbs and grasses. These results can support land managers in the decision-making process for future pinyon-juniper removal to enhance efficiency and effectiveness of treatments.