Woody exotic plant invasions and fire: reciprocal impacts and consequences for native ecosystems

Fire regimes influence and are influenced by the structure and composition of plant communities. This complex reciprocal relationship has implications for the success of plant invasions and the subsequent impact of invasive species on native biota. Although much attention has been given to the role of invasive grasses in transforming fire regimes and native plant communities, little is known about the relationship between woody invasive species and fire regime. Despite this, prescribed burning is frequently used for managing invasive woody species. In this study we review relationships between woody exotic plant invasions and fire in invaded ecosystems worldwide. Woody invaders may increase or decrease aspects of the fire regime, including fire frequency, intensity and extent. This is in contrast to grass invaders which almost uniformly increase fire frequency. Woody plant invasion can lead to escape from a grass-fire cycle, but the resulting reduction in fire frequency can sometimes lead to a cycle of rare but more intense fires. Prescribed fires may be a useful management tool for controlling woody exotic invaders in some systems, but they are rarely sufficient to eliminate an invasive species, and a dearth of controlled experiments hampers evaluation of their benefits. Nevertheless, because some woody invaders have fuel properties that differ substantially from native species, understanding and managing the impacts of woody invaders on fire regimes and on prescribed burns should become an important component of resource and biodiversity management.