Roads Impact the Distribution of Noxious Weeds More Than Restoration Treatments in a Lodgepole Pine Forest in Montana, U.S.A.

Abstract

A century of fire suppression has created unnaturally dense stands in many western North American forests, and silviculture treatments are being increasingly used to reduce fuels to mitigate wildfire hazards and manage insect infestations. Thinning prescriptions have the potential to restore forests to a more historically sustainable state, but land managers need to be aware of the potential impacts of such treatments on invasion by exotic plants. However, the effects of these activities on the introduction and spread of invasive plants are not well understood. We evaluated noxious weed occurrence over a 9-year period (2001-2009) following thinning and burning treatments in a lodgepole pine forest in central Montana. Surveys were made in the treatment units and along roads for two shelterwood-withreserve prescriptions, each with and without prescribed burning, burned only, and untreated controls. Five species listed as noxious weeds in Montana were recorded: spotted knapweed (Centaurea stoebe), oxeye daisy (Leucanthemum vulgare), Canada thistle (Cirsium arvense), common tansy (Tanacetum vulgare), and houndstongue (Cynoglossum officinale). With the exception of Canada thistle, noxious weeds were confined to roadsides and did not colonize silvicultural treatment areas. Roadside habitats contributed more to the distribution of noxious plant species than did silvicultural treatments in this relatively uninvaded forest, indicating the importance of weed control tactics along roads and underscoring the need to mitigate exotic plant dispersal by motorized vehicles. In addition, these findings suggest that roadways should be considered when evaluating the potential for invasion and spread of exotic plants following forest restoration treatments.

The Spread of Exotic Plant Species at Mount St. Helens: The Roles of a Road, Disturbance Type, and Post-disturbance Management

“…However, in the Forbdominated Blowdown Zone, exotic species did not decrease with distance from the road. These results agree with other studies that have shown roads promote the dispersal and establishment of exotic species, and that these species spread further when canopy cover decreases (Parendes and Jones 2000, Hansen and Clevenger 2005, Birdsall et al 2012, Mortensen et al 2009.…”

Aliens in Transylvania: risk maps of invasive alien plant species in Central Romania

“…All except for one study species are wind dispersed, which is an effective long distance dispersal method (Cain et al 2000). Roads serve as invasion corridors, enabling the species establishment inside disturbed road margins (Birdsall et al 2011). Environments at greatest risk of invasion away from roads appeared to be heterogeneous agricultural areas.…”

Priority Actions for Sustainable Forest Management in the International Year of Forests

“…Anthropogenic environmental stressors are accumulating globally and are a major cause of forest declines. Country reports on forest losses from disease, insect outbreaks, and wildfires (FAO 2010) do not include how such disturbances can be amplified by human‐induced stressors, including mechanized fire suppression (Kauffman 2004); simplification of forest structure, ecosystem processes, and species composition by industrial logging (Lindenmayer & Franklin 2002); road building (Birdsall et al 2011); unsustainable hunting and trapping of wild animals (Paquet et al 2006); climate‐change‐induced tree mortality (van Mantgem et al 2009); and unsustainable harvest of medicinal plants (Ndangalasi et al 2007).…”