Reviewing the Role of Wildfire on the Occurrence and Spread of Invasive Plant Species in Wildland Areas of the Intermountain Western United States

Abstract

Fire is unlikely to be a simple, deterministic process that will result in increased rates of invasion by nonnative plants. Relative dominance of nonnative plants at any postfire site likely results from a combination of factors, including propagule pressure (aboveground and belowground), time since invasion, interspecific competition, disturbance history, rainfall patterns, soil nutrients, environmental heterogeneity, land use, plus the actual fire dynamics. Consequently, the role different factors play in nonnative plant invasion is still relatively unexplained, and the possibility that wildfire may promote nonnative plant species remains a concern. Our aim was to evaluate the state of knowledge concerning how nonnative plant species establish, survive, and spread following wildfire in wildland areas for the main vegetation types of the Intermountain West. Although the particular invading species varied with vegetation type, the most frequently reported species were annual grasses (e.g., downy brome [Bromus tectorum], Japanese brome [Bromus japonicus]) and long-distance, dispersing forbs (e.g., Canada thistle [Cirsium arvense], common dandelion [Taraxacum officinale], and prickly lettuce [Lactuca serriola]). Overall, many of the reviewed studies found an increase, followed by a long-term decline, in nonnative species after wildfire, particularly when other disturbances were minimal. Regardless of this finding, many people consider rapid detection and control of new, nonnative plant populations after wildfire one of the most effective management activities. That axiom may be correct, if the nonnative propagule pressure is high and the anthropogenic disturbances are frequent, but if this is not the case the question to answer is whether immediate management, including reseeding, will benefit the system or whether off-target effects could make that approach undesirable. Continued investigation and increased quantitative analysis of the complex factors that likely contribute to changes in nonnative plants dynamics following wildfire should improve our understanding of the issue and assist managers in allocating limited resources.

Understory Cover Responses to Piñon–Juniper Treatments Across Tree Dominance Gradients in the Great Basin

“…In a study of western juniper woodlands on Steens Mountain, southeastern Oregon, Bates et al (2013) found recovery of perennial herbaceous cover after burning Phase II (codominant trees with shrubs and perennial herbs) woodlands, but Phase III (dominant trees) woodlands had limited perennial herbaceous cover both before and after severe fire. We expect continued recovery of perennial herbaceous cover on our sites where cheatgrass cover is limited and residual perennials are already well adapted to the environmental conditions (Rew and Johnson 2010).…”

Monitoring Soil Erosion on a Burned Site in the Mojave-Great Basin Transition Zone: Final Report for the Jacob Fire Site

“…Over the past 30 years, blackbrush communities have become increasingly susceptible to wildfire due to drought and invasion by non-native annual grasses (Abella, 2009;Rew et al, 2010). Fire has long-term effects on these communities which experience little regeneration (Callison et al 1985;Abella et al, 2009).…”

Spread of common native and invasive grasses and ruderal trees following anthropogenic disturbances in a tropical dry forest

“…Anthropogenic changes to ecosystems can shift community assemblages during regeneration, triggering environmental changes that influence above-and belowground dynamics (Ammondt and Litton 2012). These changes can contribute to the establishment of invasive species in the short term, but if further disturbances are minimal, the spread of an invader within an affected ecosystem may ultimately decline over the long term (Rew and Johnson 2010). On the other hand, there is limited information about overlapping effects of niche alteration and plant invasion on native communities (Didham et al 2007;Gooden and French 2014).…”

“…Disturbance can negatively influence resource acquisition and use by native trees and saplings (Hoffmann et al 2009), increase fuel loads for wildfires, and alter understory vegetation structure (Rojas-Sandoval and Acevedo-Rodríguez 2014;Hoffmann et al 2012;Cordell and Sandquist 2008;Brooks et al 2004). The process of natural regeneration after a disturbance relies on the local plant community's ability to survive in a resource-depleted ecosystem, and amidst competition from potential invasive species, before the system can regain its optimal functionality (Ammondt and Litton 2012;Rew and Johnson 2010). If implemented according to an adaptive ecosystem management framework, human-facilitated efforts to restore ecological function can provide needed support when natural regeneration seems insufficient to restore and sustain the health, productivity, and biodiversity of the system (Griscom and Ashton 2011).…”