Resource managers are using burning and thinning treatments more and more in western forests to manage the infestation of insects and disease as well as to reduce wildfire hazards. Unfortunately, these treatments can trigger the invasion and spread of invasive plants, which can thwart restoration efforts. Land managers need to be aware of this unwanted potential side effect and arm themselves with the knowledge to best monitor and treat weeds after restoration. However, the effects of burning and thinning treatments on the introduction and spread of invasive plants are not well understood.
A recently published, long-term Forest Service study conducted at the Tenderfoot Creek Experimental Forest (TCEF) in Montana helps shed some light on the spread of invasive plants. Conducted in a lodgepole pine forest in central Montana, the study involved researchers monitoring noxious weeds after thinning and burning treatments and surveying treatment units and along roads.
Researchers found five species listed as noxious weeds in Montana: spotted knapweed, oxeye daisy, Canada thistle, common tansy, and houndstongue. With the exception of Canada thistle, noxious weeds were confined to roadsides and did not colonize silvicultural treatment areas. This example highlights the importance of roads for weed distribution and spread, and suggests that the effects of roadways should be considered when evaluating the potential for invasion of exotic plants after restoration treatments.
In the TCEF, weed control along adjacent roads and in heavily disturbed areas, such as slash piles, may be a cost-effective and efficient tactic to limit exotic plant invasion. Many questions remain and more research is needed on this topic. However, it is clear that monitoring invasive plants within treated areas and along roads should be a permanent component of forest restoration.