Invasive Species

Invasive Plant Information

One significant way that invasive plants can affect the areas they are invading is by changing fuel properties, which then affects fire behavior.  The most well-known effects of plant invasions on fire regimes involve those that increase the frequency, intensity, or length of the fire season.  Collectively, these changes increase what are commonly referred to as “fire hazards.” For example, annuals grasses that have invaded shrublands can increase the frequency of fire and the length of the fire season, and invaders that increase the woody fuel load can increase fire intensity. In addition, invading plants with high tissue flammability (i.e., Eucalyptus) can ignite easier and burn more intensely.

As fire regimes and other ecosystem properties become altered, restoration of pre-invasion conditions becomes increasingly more difficult and costly. As the invasive plant infestation spreads and alters the fire regime, the number of management actions and cost to restore native ecosystem functions increases, while the probability of success decreases. This is because restoration can ultimately require managing fuel conditions, fire regimes, native plant communities and other ecosystem properties, in addition to the invaders that caused the changes in the first place.  

As with other ecological impacts caused by plant invasions, the most cost effective way to prevent the establishment of an invasive plant / fire regime cycle is to take preventative steps early on in the process.

The San Mateo County Weed Management Area is a regional organization formed by public agencies, private landowners, the agricultural industry, and environmental organizations that are concerned with invasive plant species in the county. Their top eight invasive species of concern are the yellow star thistle, jubata grass, pampas grass, French broom, Scotch broom, cape ivy, gorse, and fennel.

Fire Management and Invasive Plants

Fire management can help maintain natural habitats, increase forage for wildlife, reduce fuel loads that might otherwise lead to catastrophic wildfire, and maintain natural succession. Today, there is an emerging challenge that fire managers need to be aware of: invasive plants.  

Fire management activities can create ideal opportunities for invasions by nonnative plants, potentially undermining the benefits of fire management actions. This manual provides practical guidelines that fire
managers should consider with respect to invasive plants.

 Download the USFWS Handbook on Fire Management and Invasives.