By creating extensive ladder fuels, the non-native fern Lygodium microphyllum can alter the fire regimes of the forests it invades ©Mandy Tu

Many invasive non-native plant species are well suited for rapid dispersal into, and persistence in, altered landscapes, including those with altered fire regimes. Because fire regime alteration is widespread (The Nature Conservancy 2004), the interaction between fire and invasives is considered by many to be an urgent conservation issue. According to Brooks et al. (2004) “invaders that alter fire regimes are widely recognized as some of the most important system-altering species on the planet.”

Some examples of how invasive species intersect or interact with fire in natural landscapes around the world:

• Non-native invasive plants can alter the quantity, arrangement, and/or flammability of fuels available to burn, thus changing the way fire naturally behaves in the invaded ecosystem. Depending on the nature of fuel alteration, the result may be either the promotion or suppression of fire.
  

  If these fire regime changes favor dominance of the invaders, a cycle can become established that leads to increased ecosystem alteration over time. For example, certain fire-loving, non-native plants can dramatically increase an area’s fire frequency, creating a positive feedback loop that promotes the non-native species at the expense of native plants and animals. A well-known example is cheatgrass (Bromus tectorum), an annual grass that is now found throughout the U.S. and southern Canada and which is considered to be the worst invader in large portions of grasslands, shrublands, savanna and desert in the western U.S.
  
  There are also implications for climate change. In the Great Basin alone, expansion of cheatgrass has released an estimated 8 ± 3 teragrams of carbon into the atmosphere, and will likely release another 50 ± 20 teragrams of carbon in the coming decades. As a result, this non-native species has changed portions of the western U.S. from a carbon sink to a carbon source.
  
  

• Human-caused disruption of natural fire cycles can contribute to invasion by native or non-native species, and can eventually result in wholesale ecosystem conversion.
  
  
• Fire exclusion can result in unnaturally severe fires which, in turn, can make these areas more susceptible to invasion by non-native plant species.
  
  
• Fuel manipulation (e.g., creating fuel breaks) and post-fire rehabilitation practices can disturb soil and facilitate the invasion and spread of non-native species.
  
  
• Fire can be a useful tool for the control of some invasive plants. Treatment effectiveness can be strongly dependent on seasonality, frequency and other factors.
  
  
• The Nature Conservancy’s Invasive Species Initiative is developing tools to help mitigate invasive species problems in natural areas.
  

Selected References

• Bradley, B.A., R.A. Houghton, J.F. Mustard and S.P. Hamburg. 2006. Invasive grass reduces aboveground carbon stocks in shrublands of the Western US. Global Change Biology 12:1815-1822.
  
• Brooks, M.L., C.M. D’Antonio, D.M. Richardson, J.M. DiTomaso, J.B. Grace, R.J. Hobbs, J.E. Keeley, M. Pellant, and D. Pyke. 2004. Effects of invasive alien plants on fire regimes. Bioscience 54:677-688.
  
• Emery, S.M. and K.L. Gross. 2005. Effects of timing of prescribed fire on the demography of an invasive plant, spotted knapweed Centaurea maculosa. Journal of Applied Ecology 42(1):60-69.
  
• Galley, K.E.M. and T.P. Wilson. 2001. Editors. Proceedings of the Invasive Species Workshop: the Role of Fire in the Control and Spread of Invasive Species. Fire Conference 2000: the first National Congress on Fire Ecology, Prevention, and Management. Miscellaneous Publication No. 11, Tall Timbers Research Station, Tallahassee, FL.
  
• Keeley, J.E. 2003. Fire and invasive plants in California ecosystems. Fire Management Today 63(2):18-19.
  
• Lesica, P., and B. Martin. 2003. Effects of prescribed fire and season of burn on recruitment of the invasive exotic plant, Potentilla recta, in a semiarid grassland. Restoration Ecology 11:516-523.
  
• The Nature Conservancy. 2004. Fire, Ecosystems and People. A Preliminary Assessment of Fire as a Global Conservation Issue. http://nature.org/initiatives/fire/science.
  
• van Wilgen, B.W., and D.M. Richardson. 1985. The effects of alien shrub invasions on vegetation structure and fire behavior in South African fynbos shrublands: a simulation study. Journal of Applied Ecology 22:955-966.