PS 11-153 - Science and application at the nexus of fire and invasive plant management in western forests

Abstract: Land managers and practitioners are increasingly being called upon to focus on the intersection between fire and invasive plant management. Changing climatic conditions, past and present land-use, novel fire behavior, threats to humans and natural ecosystems, and the ever-increasing pipeline of new invasive species all exacerbate the need for knowledge, tools, and science delivery at this nexus. Few contemporary comprehensive and end-user friendly state-of-the-science syntheses exist for this topic, particularly for forests. To address this gap, we conducted a literature review and gathered feedback from invasive plant managers in the western US. We present past, present and potential future invasive plant and fire challenges specific to western forests, review management strategies, discuss challenges posed by land-use and global change, and identify emerging bioregional issues and risks. Information will be part of a chapter in an upcoming book covering the fire and invasive plant management issues in the United States.

We found that despite perceptions of invasion resistance, shade tolerant invaders are commonly reported in the literature and on the ground in many western forests. However, shade intolerant species are most problematic. Forests vary in canopy openness and are composed of complex spatial mosaics of vegetation types, including non-forested plant communities that vary in size, including agro-pastoral areas, early seral disturbance driven patches, and persistent openings such as meadows.

Invasive grasses are a growing threat for many forests. Species including ventenata (Ventenata dubia), cheatgrass (Bromus tectorum), other bromes, and medusahead (Taenatherium caput-medusae) are commonly associated with rangeland ecosystems, but have been observed heavily invading burned forests, especially at the rangeland-forest ecotone in drier forests. Invasive grasses can also be problematic after disturbances in more mesic forests and oak woodlands in the northwest. Many forbs such as dalmatian toadflax (Linaria dalmatica) and others (thistles, mullein) are problematic in southwestern forests and the Rocky Mountains. Species that introduce novel fuel types into forests, such as pyrophytic shrubs and annual and perennial grasses encourage or suppress fire spread and may alter fire regimes. Lack of understanding regarding the ecological consequences and importance of managing invasive plants in tandem with fire and fuel management may lead to unintended and problematic outcomes as we enter an age of novel and rapid ecological changes.