Analysis of largest ever, cross-boundary conifer removal efforts in the sagebrush biome showed projects achieving management goals and validated need for coupled management of invasive annual grasses.
Conifer encroachment – the process where native trees like juniper and pinyon pine move from historic habitats (higher elevations, wet and cooler areas) into sagebrush rangeland – is responsible for more than 20% of declines in sagebrush ecological integrity since 1990, making it one of the top threats to the biome. New WLFW-affiliated science shows strategic tree removal treatments are effective, while also calling for added focus on treating invasive annual grasses to most effectively restore and conserve healthy sagebrush rangelands.
When trees move into native, formerly tree-free sagebrush rangelands, a cascade of impacts follows. Sage grouse will abandon otherwise suitable habitat when just a few trees per acre are present. Trees sap precious moisture from the soil, making it harder for native shrubs and perennials to grow. Without these native plants, wildlife, and livestock struggle to find forage. Trees also make wildfires worse across the sagebrush biome.
Because of these impacts, conifer removal is a key component of Working Lands for Wildlife’s efforts in sagebrush country. Since 2010, the Sage Grouse Initiative (part of WLFW) has targeted conifer removal projects in areas of large, intact sagebrush rangelands where sage grouse would most benefit from removal efforts. Many of these locations, including the two projects included in the study featured below, cross public and private lands, making partnerships and cross-boundary work pivotal to conservation success.
This partnership-based and targeted approach to conifer management is linked to positive demographic responses for sage grouse and sagebrush songbirds, and better conservation outcomes than more random, dispersed treatments.
However, WLFW researchers had yet to evaluate the long-term effects of conifer removal efforts on vegetation and the durability of conservation gains obtained through conifer removal.
WLFW researcher Joe Smith led a team that evaluated the vegetative outcomes of two large conifer removal efforts using the Rangeland Analysis Platform and then compared changes in their ecological integrity before and after management according to the new Sagebrush Conservation Design. The SCD, published in 2022, used advanced remote sensing technology to classify the entire sagebrush biome into Core Sagebrush Areas, Growth Opportunity Areas, and Other Rangeland Areas and to evaluate the most significant threats impacting the biome.
This paper is part of a special issue of the Journal of Rangeland Ecology and Management that includes 19 other articles that delve into the science of how, where, and why conservationists are deploying strategic conservation to save the sagebrush biome. Learn more and find all the papers and other resources at the Sagebrush Conservation Gateway.
Both efforts featured in the study are in southern Idaho and are the result of an enduring partnership between the state of Idaho, WLFW and USDA-NRCS, the Bureau of Land Management, the Idaho Governor’s Office, and other partners. One of the projects, the BOSH or Bruneau-Owyhee Sagebrush Habitat project, is now the largest restoration project in the sagebrush biome. Between public (BLM) and private lands treatments (WLFW/NRCS), the BOSH partners are removing conifers from more than 617,000 acres of sagebrush range and still have several years of work ahead.
The team used remotely sensed vegetation data to evaluate mechanical removal treatments for 288 private and public land parcels covering more than 247,000 acres. They contrasted the conservation outcomes of those treatments against 64 different wildfires that collectively burned approximately 370,000 acres of rangelands in the region.
They found that sustained, focused implementation of tree removal treatments can effectively halt the second leading driver of sagebrush ecosystem degradation while restoring the foundations of a healthy sagebrush plant community. Additionally, cross-boundary projects like these can achieve significant scale when partners work together to address threats across public and private lands.
Across all phases of encroachment, mechanical treatments proved more successful than wildfire at removing tree cover and increasing perennial grass and forb production. In later phases of encroachment, treatments boosted shrub presence. Perennial grasses and forbs provide important food resources for livestock and wildlife and shrub cover is a key component of habitat for sagebrush-dependent wildlife like sage grouse.
The team found that invasive annual grasses – the largest single driver of declines in sagebrush ecological integrity since 1990 – increased in most of the treatments, particularly in the first two to three years following removal. However, by year seven, competition from native perennials reduced invasive annual grass abundance by half.
While these long-term results show that perennials return given enough time, they highlight the need for managers and practitioners to implement conservation treatments that address invasive annual grasses to ensure long-term durability of conservation investments.
Overall, the team found that SGI’s targeted mechanical treatments halted or reversed declines in sagebrush ecological integrity due to conifer encroachment in the watersheds evaluated, effects that extended across private and public lands due to the cross-boundary nature of the treatments.
These findings add to a growing body of evidence supporting benefits from targeted, large-scale conifer management. Partnerships are, of course, critical to the scale needed to conserve prime sagebrush habitat from threats like conifers. Because these projects include both private and public lands and are some of the largest projects of their type, they provided excellent case studies.
WLFW’s outcomes-based approach, outlined in its Framework for Conservation Action in the Sagebrush Biome, provides the flexibility and targeting required to ramp up invasive annual grass management while also addressing other top-level threats to the biome.
Given the widespread impacts of both conifer encroachment and invasive annual grasses in the sagebrush biome, this research provides immense value for managers and practitioners working to proactively defend sagebrush cores from two of the most pervasive threats in the biome.
USING SATELLITE REMOTE SENSING TO ASSESS SHRUBLAND VEGETATION RESPONSES TO LARGE-SCALE JUNIPER REMOVAL IN THE NORTHERN GREAT BASIN
Abstract: Woody encroachment into grasslands and shrublands disrupts ecosystem processes and reduces biodiversity. Tree removal is a widespread strategy to restore ecosystem services and biodiversity in impacted landscapes. However, tree removal can also increase the risk of invasion by exotic annual grasses. In western North America, juniper (Juniperus spp.) encroachment threatens the ecological integrity of intact sagebrush (Artemisia tridentata) shrublands.
We used remote sensing to track vegetation changes following juniper removals on 288 parcels totaling 106,333 ha in southern Idaho, USA. We also analyzed vegetation changes following 64 wildfires that burned 152,611 ha of nearby rangeland during the same period. We matched areas within removals and wildfires to similar undisturbed areas, and then used causal impact analysis to estimate the effects of the disturbances.
Juniper removals resulted in sustained reduction of tree cover and increased perennial forb and grass cover across nearly all sites, achieving key management goals. Based on the metrics evaluated, juniper removal was more effective than wildfire in delivering long-term restoration in this sagebrush system. However, juniper treatments also stimulated temporary undesirable increases in annual grasses and forbs, indicating the need for additional management to achieve durable conservation outcomes.
Intensive mechanical methods initially reduced shrub cover in some treatments, but shrubs recovered to near pre-treatment levels within 7 years. Using a recently developed metric of ecological integrity for sagebrush ecosystems, we show that these large, long-term projects halted or reversed degradation attributed to juniper expansion, demonstrating that restoration can improve the trajectory of ecosystems when implemented at scale.
Citation: Joseph T. Smith, Andrew R. Kleinhesselink, Jeremy D. Maestas, Scott L. Morford, David E. Naugle, Connor D. White, “Using Satellite Remote Sensing to Assess Shrubland Vegetation Responses to Large-Scale Juniper Removal in the Northern Great Basin,” Rangeland Ecology & Management, Volume 97, 2024, Pages 123-134.
Permanent URL: https://doi.org/10.1016/j.rama.2024.08.010
Acknowledgements: This project was supported by BLM Montana/Dakotas as well as Partnering to Conserve Sagebrush Rangelands, a partnership between BLM and the Intermountain West Joint Venture. We thank Tate Walters and Connie Tharp with the Natural Resources Conservation Service and private landowners in the project areas for assistance with assembling and providing permission to include private lands data in this analysis.