A JFSP Fire Science Exchange Network
Bringing People Together & Sharing Knowledge in the Northern Rockies

Invasive grasses increase fire occurrence and frequency across US ecoregions

Author(s): Emily J. Fusco, John T. Finn, Jennifer Balch, R. Chelsea Nagy, Bethany A. Bradley
Year Published: 2019

Fire-prone invasive grasses create novel ecosystem threats by increasing fine-fuel loads and continuity, which can alter fire regimes. While the existence of an invasive grass-fire cycle is well known, evidence of altered fire regimes is typically based on local-scale studies or expert knowledge. Here, we quantify the effects of 12 nonnative, invasive grasses on fire occurrence, size, and frequency across 29 US ecoregions encompassing more than one third of the conterminous United States. These 12 grass species promote fire locally and have extensive spatial records of abundant infestations. We combined agency and satellite fire data with records of abundant grass invasion to test for differences in fire regimes between invaded and nearby 'uninvaded' habitat. Additionally, we assessed whether invasive grass presence is a significant predictor of altered fire by modeling fire occurrence, size, and frequency as a function of grass invasion, in addition to anthropogenic and ecological covariates relevant to fire. Eight species showed significantly higher fire-occurrence rates, which more than tripled for Schismus barbatus and Pennisetum ciliare. Six species demonstrated significantly higher mean fire frequency, which more than doubled for Neyraudia reynaudiana and Pennisetum ciliare. Grass invasion was significant in fire occurrence and frequency models, but not in fire-size models. The significant differences in fire regimes, coupled with the importance of grass invasion in modeling these differences, suggest that invasive grasses alter US fire regimes at regional scales. As concern about US wildfires grows, accounting for fire-promoting invasive grasses will be imperative for effectively managing ecosystems.

Citation: Fusco, Emily J.; Finn, John T.; Balch, Jennifer K.; Nagy, R. Chelsea; Bradley, Bethany A. 2019. Invasive grasses increase fire occurrence and frequency across US ecoregions. Proceedings of the National Academy of Sciences of the United States of America 116(47):23594-23599. https://doi.org/10.1073/pnas.1908253116
Topic(s): Fire Effects, Ecological - Second Order, Invasive Species, Fire Regime, Fuels
Ecosystem(s): None
Document Type: Book or Chapter or Journal Article
NRFSN number: 20435
FRAMES RCS number: 59092
Record updated: Dec 16, 2019