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Invasive plants that establish in sagebrush steppe ecosystems during the critical post-fire recolonization period can affect long-term vegetation community trajectories.

In Idaho, USGS researchers evaluated post-fire responses of the exotic perennial forb rush skeletonweed (Chondrilla juncea) and its biocontrol agents – gall midge, gall mite, and rust fungus – in relation to landscape factors affecting water availability. They also examined effects of a combined herbicide (imazapic) and bacteria (Pseudomonas fluorescens strain MB906) spray treatment that targeted invasive annual grasses. Rush skeletonweed 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. Biocontrol infestation levels varied considerably between species and years. Results suggest that spatial patterns of rush skeletonweed invasion are related to deep-soil water availability, warmer conditions, and alleviation of competition. Treatments designed to reduce invasive annual grasses may inadvertently release rush skeletonweed by both reducing plant competition for soil resources and suppressing mite abundance.  

Lazarus, B.E., Germino, M.J., 2021, Post-fire management targeting invasive annual grasses may have inadvertently released the exotic perennial forb Chondrilla juncea and suppressed its biocontrol agent: Biological Invasions, online,

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