Research gaps limit understanding of invasion-fire cycles

Abstract

Invasive plants can alter fuels and fire regimes in ways that facilitate their spread and dominance through a process known as the invasion-fire cycle. This phenomenon can result in considerable fire and ecosystem impacts, but mechanisms, habitat susceptibility, and prevalence of invasion-fire cycles are poorly understood. Here, we reviewed literature on invasion-fire cycles and describe how mechanisms by which and habitats in which invasion-fire cycles occur are influenced by invader growth form, including woody versus herbaceous and perennial versus annual species, among other factors, and highlight research needs to better understand invasion-fire cycles. We found evidence that annual herbaceous species facilitated more continuous and frequent fires in shrublands and deserts by increasing fine fuel continuity, while perennial grasses and woody invaders more often facilitated intense and vertically continuous fires in forest habitats by increasing fuel loads. There was some evidence woody invaders can suppress fires by decreasing fine fuels, and both woody invaders and perennial grasses and forbs can inhibit fires due to high fuel moisture and low flammability, but effects of fire suppression by invaders on native communities were ambiguous. Fire suppression and climate change may complicate effects of invasions on fire regimes directly, or indirectly through shifting abundances of fire prone or fire adapted native plant species. More research is needed to understand how propagule pressure, ignitions, climate, and resource availability affect invasion-fire cycles, and to determine relative importance of invasion-fire cycles in driving plant invasions and effects of invader driven changes to fire regimes on native communities.