Severity of fungal disease did not result in measurable reductions of populations of a non‐native, invasive host species, cheatgrass, which suggests that natural enemies may not strongly regulate cheatgrass in its introduced range. Landscape heterogeneity associated with disturbance and weather limited population‐level infection of hosts by the fungal pathogen. Disturbance (specifically wildfire) and variable weather are key components of this and similar invasion systems, and likely need to be considered when evaluating disease dynamics and potential for natural enemies to influence invasion potential.
Top-down and bottom-up factors affecting invasive populations are rarely considered simultaneously, yet their interactive responses to disturbances and management interventions can be essential to understanding invasion patterns. We evaluated post-fire responses of the exotic perennial forb Chondrilla juncea (rush skeletonweed) and its biocontrol agents to landscape factors and a post-fire combined herbicide (imazapic) and bacteria (Pseudomonas fluorescens strain MB906) treatment that targeted invasive annual grasses in a sagebrush steppe ecosystem. Biocontrol agents released against C. juncea in previous decades included Cystiphora schmidti (gall midge), Aceria chondrillae (gall mite), and Puccinia chondrillina (rust fungus). C. juncea abundance was greater in sprayed than unsprayed plots, and where soils were coarser, slopes faced southwest, solar heat loads and topographic water accumulation were greater, and cover of deep-rooted native perennials was lower. Mite infestation was greater in unsprayed plots, midge infestation was greater at higher elevations on steeper slopes, and midges were more abundant while rust was less abundant on gravelly soils. Biocontrol infestation levels varied considerably between years and could not be predicted in 2019 from 2018 infestation levels. Multiple biocontrol species were often present at the same plots but were rarely present on the same C. juncea individuals. These results suggest that spatial patterns of invasion by C. juncea are related to deep-soil water availability, warmer conditions, and alleviation of competition. Treatments designed to reduce invasive annual grasses may inadvertently release C. juncea by both reducing plant competition for soil resources and affecting biocontrol agent (mite) abundance.
A treatment targeting a single plant functional group did not achieve lasting success in these diversely invaded communities. Spraying alone did not release native perennials sufficiently to counteract the simultaneous release of secondary invaders and the return of target invaders. Planting or seeding may also be needed to achieve management goals.
Cheatgrass invasion decreases biodiversity and rangeland productivity and alters fire regimes. Our findings indicate cheatgrass invasion also results in persistent biomass carbon (C) losses that occur with sagebrush replacement. We estimate that conversion from native sagebrush to cheatgrass leads to a net reduction of C storage in biomass and litter of 76 g C/m2, or 16 Tg C across the Great Basin without management practices like native sagebrush restoration or cheatgrass removal.
Invasive Species in Forests and Rangelands of the United States is a sector-wide scientific assessment of the current state of invasive species science and research in the United States. Leading experts on invasive pests, climate change, social sciences, and forest and rangeland management contributed to highlighting the science and identifying knowledge gaps on a diverse array of topics related to invasive species. Stakeholders from nongovernmental organizations, academic institutions, professional organizations, private corporations, and state and federal agencies representing public, private, and tribal interests also provided input to the assessment. Input from these stakeholders helped to frame the subject matter content and management options presented in this report, ensuring relevance for decision-makers and resource managers.
The following topics and presenters are included:
Cheatgrass Impacts and Management Options in Western U.S. Ecosystems, presented by Ali Urza and Brice Hanberry
Impacts of Invasive Cogongrass on Private and Public land: Prevention and Control Strategies, presented by Rima Lucardi
Ventenata Invasion in the Western U.S.: Using Remote Sensing & Model Output to Understand Invasion Risk, presented by Becky K. Kerns
We are hosting several workshops, symposia as part of the 2021 Society for Range Management annual meeting. **You do not need to be registered for the SRM meeting to attend.
Strategic Targeted Grazing to Reduce Fine Fuels (Feb 16, 1:30-4:00 PST/2:30-5:00 MST)
The Strategic Grazing symposium was held in conjunction with the Society for Range Management Virtual Meeting. It provides updates on the Idaho and Nevada strategic grazing demonstration areas. Symposium recording.
Sagebrush Ecosystem Recovery 10+ Yrs after Treatments (Feb 17, 1:30-3:30 PST/2:30-4:30 MST)
The Sagebrush Ecosystem symposium provides Sagebrush Steppe Treatment Evaluation Project (SageSTEP) updates. It was held in conjunction with the Society for Range Management Virtual Meeting. It shares what’s been learned after at least 10 years post-treatment. Symposium recording.
Big Sagebrush Restoration Status (Feb 18, 1:30-4:00 PST/2:30-5:00 MST)
The Big Sagebrush symposium was held in conjunction with the Society for Range Management Virtual Meeting. It was brought to you by the Rangeland Equipment and Technology Council (RTEC). Symposium recording.
The Sagebrush Ecosystem Recovery symposium will provide Sagebrush Steppe Treatment Evaluation Project (SageSTEP) updates. It will be held in conjunction with the Society for Range Management Virtual Meeting. It will share what’s been learned after at least 10 years post-treatment. **You do not need to be registered for the SRM meeting to join.
Abstracts of Recent Papers on Range Management in the West. Prepared by Charlie Clements, Rangeland Scientist, USDA Agricultural Research Service, Reno, NV.
Disturbance events, such as overgrazing and the catastrophic fires, in our shrub steppe landscape can kick-start a negative feedback loop with invasion of noxious weeds. These invasive species can have a direct effect on services and ecological benefits provided by the shrug steppe landscape. Learn what we can do to minimize the spread of invasive plant species and how native seeds and grasses can be used to restore this brittle system.