Summary

The synergistic impacts of multiple anthropogenic global change stressors, like drought, wildfires and invasion by non-native species, on natural systems is not widely studied. Fire intensity and frequency play an important role in determining plant composition post-fire, however, it is unclear how drought and fire characteristics impact recovery of native vs non-native plants. Kimball et al., conducted a rainfall manipulation experiment in coastal sage shrub environment to test the hypothesis that reduced rainfall, fuel load and fire severity caused by drought lead to higher invasion after fire.

Reduced water plots had lower native shrub cover and overall lower biomass compared to increased water plots, which were dominated by native shrubs. This lower biomass resulted in less severe fires and a conversion of plant community composition to non-native grasses. Increased water plots had higher native biomass and higher fuel load pre-fire, which resulted in a more severe fire and native shrub-dominated plant community post fire.

Take-home points:

  • Increased water plots saw higher fuel loads, dominated by native shrubs. These high fuel loads resulted in higher fire severity.
  • Native shrubs have adapted to fires and recover from high severity fires more easily than non-natives, which are typically generalists.
  • Reduced water plots (simulating drought) had reduced plant cover and fuel load, leading to reduced severity of fire.
  • Invasive plants were found to dominate high-frequency, low-severity fire environments.

Management Implications:

  • While severe fires can be harmful to forest systems, in fire-adapted systems like those in Southern California, they can limit invasive species spread and promote native plants’ recovery after fires.
  • Management strategies need to consider life history traits of native plant communities. Prescribed burning is recommended to reduce fuel load and fire severity in forest systems but should not be used in fire-adapted systems like CSS.