The human-grass-fire cycle: how people and invasives co-occur to drive fire regimes

Invasive grass species can alter fire regimes, converting native terrestrial ecosystems into non-native, grass-dominated landscapes, creating a self-reinforcing cycle of increasing fire activity and flammable grass expansion. Analyses of this phenomenon tend to focus on the ecology and geography of the grass-fire cycle independent of human activities. Yet people introduce non-native grasses to new landscapes (eg via agriculture), facilitate their spread (eg via road networks), and are a primary source of ignition (eg via debris burning). We propose a new framework for this phenomenon that explicitly recognizes the important role of anthropogenic activities in the human-grass-fire cycle. We review links between land use and invasive species as well as ignitions, with a particular focus on the spatial and temporal co-occurrences of these activities to show that these two drivers of wildfires are inextricable. Finally, management strategies that could mitigate impacts are discussed.