Fuel Moisture Differences in a Mixed Native and Non-Native Grassland: Implications for Fire Regimes

Abstract

Non-native plants have far-reaching effects on many terrestrial ecosystems. There are several examples of non-native species altering fire regimes, either by increasing or decreasing the potential intensity and severity of fires. To investigate this phenomenon, we sampled fuel moisture content of four native grass species (Festuca californica Vasey, Danthonia californica Bol., Elymus glaucus Buckley, and Bromus carinatus Hook. & Arn.) and four non-native grass species (Phalaris aquatica L., Cynosurus echinatus L., Arrhenatherum elatius [L.] J. Presl & C. Presl, and Anthoxanthum odoratum L.) in northern California grasslands across the 2012 growing season. No significant differences in moisture content were found between native and non-native groups (P = 0.337). Across all dates, moisture content of the eight grass species differed (P < 0.001). The non-native annual Cynosurus echinatus had the lowest moisture content in August (21 %), and fell well below ignition thresholds before the other grasses. Phalaris aquatica, an aggressive perennial non-native, had the highest moisture content for all months and differed significantly from all species for all dates (P < 0.05). Our results suggest that some non-native species have the capacity to alter fire behavior by either increasing or decreasing fire intensity and rate of spread. These findings reveal another way non-native species complicate restoration and management of fire-dependent ecosystems.