Fire season and drought influence fire effects on invasive grasses: A meta‐analysis

Abstract Fire can shape plant communities when species respond differently to fire characteristics like season and intensity. If invasive plants are more vulnerable than native species to specific aspects of fire, managers could use prescribed fires to control non‐native species. We conducted a meta‐analysis of fire effects on six closely related Afro‐Eurasian and Australian grasses ( Bothriochloa bladhii , B. ischaemum , B. pertusa , Dichanthium annulatum , D. aristatum and D. sericeum , collectively ‘invasive bluestems’) that have invaded grasslands worldwide. Using data from 31 studies (only 3 from their native range), we evaluated whether these grasses (275 effect sizes) responded differently than native grasses (184 effect sizes) to fire season, fuel load and drought. Original data included 15 different response variables (e.g. biomass, survival) that were converted to standardized mean difference for analysis. Fires in summer, fall and early winter had negative effects on invasive bluestems; no fire season had significant positive effects. Most data were for B. ischaemum , but the other bluestems may also be vulnerable to summer fire. Native grasses did not show significant negative responses in any month. Drought (Keetch–Byram Drought Index) in the month before fire increased the negative effects of fire on invasive bluestems but not native grasses. Drought after fire led to similar negative effects on both groups. Unexpectedly, fuel load (which influences fire intensity) did not significantly influence fire effects in any analysis. At the fuel loads examined (~600–10,000 kg/ha dried herbaceous biomass), fire intensity may have been too low to cause meristem mortality. Between‐study heterogeneity was large in all analyses ( I 2 > 80%), suggesting that additional factors beyond those reported in the studies influence fire effects. These factors could include plant phenology, fire behaviour, weather conditions during the fire and soil characteristics. Synthesis and applications : Fires during summer and fall, especially during dry conditions, could harm invasive bluestems relative to native grasses, likely due to subtle differences in heat sensitivity, phenology and drought resistance. Other invasive species may have similar vulnerabilities to specific fire seasons and rainfall conditions that allow the use of fire as a control method.