Ecological effects of pinyon-juniper removal in the Western United States—A synthesis of scientific research, January 2014–March 2021

First posted June 21, 2023 For additional information, contact: Director, Forest and Rangeland Ecosystem Science Center777 NW 9th Street, Suite 400Corvallis, OR 97330 Increasing density of pinyon (Pinus spp.) juniper (Juniperus woodlands (hereinafter “pinyon-juniper”), as well expansion these into adjacent shrublands grasslands, has altered ecosystem function wildlife habitat across large areas the interior western United States. Although there are many natural human-caused drivers woodland infilling expansion, restoration sagebrush (Artemisia through removal pinyon-juniper is considered an urgent management objective in locations, particularly support sagebrush-dependent species conservation concern. In December 2020, Bureau Land Management (BLM) established Pinyon-Juniper Categorical Exclusion (PJCX) to expedite regulatory process for projects on public lands, largely intended benefit mule deer (Odocoileus hemionus) greater sage-grouse (Centrocercus urophasianus) habitats. During final preparation this report, BLM discontinued use PJCX (as November, 2022), but tree techniques assessed report commonly used understanding their effects remains relevant land planning.To address uncertainty relative potential ecological PJCX, we conducted a review peer-reviewed science literature better understand likely responses vegetation, environmental (for example, soils), variables specific permitted by PJCX. brief, trees either manual cutting, mechanical or mastication; allowed certain methods redistribute remove resulting biomass after treatment; prohibited broadcast burning, roadbuilding, old-growth, seeding non-native species. Specifically, our following questions:How will affect plant communities, soils, abiotic resources?How do including both woodland- species?What implications different treatment types implementation strategies sizes) over time?What most important gaps scientific how treatments might targeted ecosystems space time climate change)?To answer questions, studies related ecosystems, focusing research that occurred portion States primary focus We also focused papers published from 2014 onward, avoid excessive overlap with other recent reviews effects. Using strict criteria, only considering tested statistical significance, identified 48 primarily examined vegetation (1,709 responses), 11 addressed (132 responses). Responses PJCX-permitted were summarized positive (that is, significant increase), negative decrease), non-significant no difference). assigned categories Native Annual Grass/Forb Abundance) hierarchical levels.We found proportions among all combined, roughly half more (48 percent wildlife, 60 vegetation-environmental), comparable systematic However, when responses, some trends potentially emerged. Important undesirable outcomes included far than exotic grass forb abundance nearly types. Cutting decrease biocrust cover microbial activity. Potentially beneficial mostly obligate species, sage-grouse. Some mastication) resulted native grasses forbs (although, majority). highlighted limitations review, often come few studies, response-treatment category combinations lack adequate response data. Moreover, existing insufficient key questions about effects, owing short time-scales limited spatial extents observations, which not match size being implemented managers, nor capture long-term, post-treatment dynamics. identify addresses interactions could undermine objectives, change grazing environments. Thus, emphasize importance integrating factors future research, stress need monitoring programs partake data collection analysis long durations broad scales.