Invasive cheatgrass on the range.

Invasive Species Alter Fire Regimes and Fire Operations

By Ken Frederick

They have been called everything from the “bane of the rangeland” to a “biological emergency.”  “They” are invasive species, and they tend to draw disdain from all corners of resource management.  For the fire community, they mean more frequent, high-intensity fires that burn with extremely rapid rates of spread.

Those invasives then return quickly after a fire and further dominate and encroach into new areas, leading to a cycle of “quickly burn and rapidly return” that eventually pushes native grasses and shrubs out of their habitat.  Postfire reseeding and rehabilitation efforts under the right conditions and in the right locations can help stem that tide.  Unfortunately, invasive species have already established an unhealthy monoculture across large areas of the West.  Nearly every area is feeling at least some effect of these invaders.

While climate change and the explosive growth of the wildland-urban interface are often considered the most dramatic agents of change affecting wildland fire, invasive species are a significant culprit in the size and frequency of fires throughout the West.  For instance, invasive species, with their flammability and tendency to carry fire, have been a major factor in some of the West’s largest fires in the mid-2000s. 

In 2005, fires in Arizona burned nearly 250,000 acres of the Sonoran Desert, many in areas where fire had never before been recorded.  Fires encroached into these areas thanks to the spread and flammability of invasive species.  In early 2006, hundreds of fires (aided by invasive species) burned nearly a million acres in the Chihuahuan Desert of west Texas.

In 2007, the Murphy Complex Fire burned more than 650,000 acres in Idaho and Nevada, and the Milford Flat Fire, the largest in Utah history, scorched more than 363,000 acres.  Overall, between 1990 and 2008, more than 21 percent—16 million acres—of the Great Basin had burned at least once, according to a Great Basin Restoration Initiative report.

Although ecologists point out numerous invasive species with wildfire implications, several stand at the top of the list:

• Cheatgrass – An annual grass, this species already dominates some 25 million acres in the Great Basin alone.  Cheatgrass germinates in the fall, overwinters as a seedling, and grows rapidly in the spring.  By early summer, cheatgrass has already completed its life cycle.  The dead, dried out plants create an exceptional fuel bed for wildfire.

• Medusahead – Another winter annual, medusahead occupied an estimated 2.3 million acres in the early 2000s.  It commonly follows, and then replaces, cheatgrass.  Because it is high in silica, dead medusahead plants decompose slowly and remain available as a fuel for wildfire for several years.

• Buffelgrass – An African perennial grass, buffelgrass was introduced into the United States in the 1930s as livestock forage.  Currently, buffelgrass is present on an estimated tens of thousands of acres in 12 states, primarily across the southern third of the United States.  Buffelgrass is a threat because it increases the frequency and intensity of wildfires in the ecosystems it invades.  Like its cousins, buffelgrass responds well to fire and recolonizes burned areas faster than native grasses, shrubs, and cacti.

• Western Juniper – Though native to arid western ecosystems, juniper has taken advantage of fire exclusion to move out of its historic habitat and invade new areas.  Juniper affects fire regimes by displacing native plants from a landscape.  Once juniper is well established, its thick stands fuel high-intensity wildfires when weather conditions favor ignition and spread.  The hot-burning juniper fires often burn everything, essentially pushing the ecological “reset” button in the fire area.  Unfortunately, all too often, the burned ground is quickly invaded by invasive annual grasses.

Whether they are a “biological emergency” or a “bane on the rangeland,” most experts agree that invasive species are here to stay and that they will continue altering fire regimes and affecting BLM firefighting operations.  Firefighters will continue to face complex, rapidly spreading fires that burn with unusually high intensity across the BLM landscape.

Ken Frederick was a firefighter for more than a decade prior to entering public affairs.  His career has included stops in Washington, Arizona, and Idaho.  He is currently a public affairs specialist at the National Interagency Fire Center in Boise, Idaho.