Scotch broom (Cytisus scoparius (L.) Link) is a non-native, invasive shrub which rapidly dominates recently disturbed sites and alters ecosystem function. The species is of major concern in forests and prairies of Joint Base Lewis McCord (JBLM) where it hinders training activities, outcompetes native vegetation, and drives loss of native ecosystems and habitat for endangered and threatened species. The goal of this project is to develop comprehensive approaches for the control of Scotch broom on Department of Defense (DoD) lands to support military training needs, minimize impacts to ecosystem functions, and eventually support habitat for endangered, threatened, and special concern species. The specific objectives of this project are to:

  1. Evaluate a suite of novel Scotch broom control strategies to determine their efficacy at increasing the competitiveness of native tree species (Douglas-fir, Oregon white oak, and Ponderosa pine) with Scotch broom.
  2. Determine how time-since-invasion influences Scotch broom legacy effects (seedbank dynamics and allelopathy) and how this might change under future climate or in response to management actions (i.e., biochar application to immobilize allelopathic compounds).

Technical Approach

The project team will test physical, chemical and thermal eradication methods designed to control broom while simultaneously reducing the broom seedbank. These methods will be tested in conjunction with planting resilient, climate-adapted tree species and genotypes which are expected to be resistant to Scotch broom’s allelopathy, as well as drought and fire. The research approach has two primary components: Component 1 will evaluate efficacy of novel control treatments and evaluate concurrent effects on plant communities using a replicated field experiment. Component 2 will evaluate how invasion duration impacts the broom seedbank, potential allelopathy, and vegetation communities using field and laboratory assessments. The experimental design for Component 1 will be a completely randomized split-split plot design with four whole-plot levels (control [no removal], clip broom and remove biomass, broom mechanical mastication, and prescribed fire), combined with split plot herbicide and tree species treatments. For Component 2, twenty sites that span a range of 1-25 years since Scotch broom invasion will be identified. Among sites the project team will (i) record plant species percent cover, (ii) conduct soil chemistry characterization, (iii) assess potential allelopathy on the three species from Component 1, (iv) evaluate broom seedbank viability under future climate and (v) test ability of biochar to immobilize allelopathic compounds.


Findings will be used to identify the most effective broom control strategies that also minimize impacts to native plant communities, which will allow JBLM staff to reduce their extensive herbicide-focused control efforts, freeing up resources to focus on achieving the broader DoD mission related to military training and readiness. This project will also advance the scientific understanding of the soil legacy effects associated with Scotch broom and their role in increasing the distribution and abundance of Scotch broom by outcompeting native species. Lastly, the project team expects that the findings will benefit the broader natural resources management community with methods and approaches to combat this aggressive invasive shrub throughout the region.

  • Management of invasive plants (grasses; bushes etc.),