The Whittier Fire burns in the mountains above above Goleta, California.

Flames flicker in the hills above Goleta, California. Non-native weeds infiltrating the state’s scrublands and woods have raised the risk of fire. Credit: Brian Stetson/Alamy

Environmental sciences

Rampaging weeds help to set the US landscape ablaze

Iconic landscapes of the western United States are more likely to burn if they are overrun by invasive grasses.

Invasion by non-native grasses sharply increases fire risk in a variety of ecosystems across the continental United States, from deciduous forest in the east to the deserts of the southwest.

Emily Fusco at the University of Massachusetts, Amherst, and her colleagues used government records, satellite fire data and computer models to analyse the impact of 12 species of non-native grasses on fire trends in 29 US ecological regions. The researchers then compared these patterns in invaded and uninvaded landscapes.

The results showed that fire had burned more of a habitat riddled with one of eight weed species than the same type of habitat without the invader. For example, flames had torched 2.3 times as much dry shrubland invaded by Schismus barbatus grass than dry shrubland free of this species. Of the eight fire-promoting weeds, six increased fire frequency in the ecosystems that they had invaded.

The authors suggest that the presence of invasive grasses should be considered more prominently in future land-management plans.