Data for: Long-term drought reduces wildfire severity and promotes invasive species

Anthropogenic climate change has increased the frequency of extreme
drought, wildfires, and invasions of non-native species. Studying
interactions amongst these multiple stressors is rarely done at the local
scale yet is key to anticipating impacts on vulnerable ecosystems. We
leveraged an existing experimental rainfall manipulation to evaluate the
relationship between precipitation, fuel load, and fire severity in a
Southern California coastal sage scrub system. We asked whether pre-fire
rainfall manipulation influenced fuel load and vegetation cover with
consequences for fire severity and post-fire community composition. We
measured plant biomass and community composition before and after the 2020
Santiago wildfire in experimental plots with three rainfall treatments.
After fire, we measured number of branches, diameter of the smallest
terminal branch, leaf percent cover, and height on three dominant native
shrub species (Malosma laurina, Artemisia californica, and Salvia
mellifera) to assess fire severity. Native shrubs had greater pre-fire
cover in added water plots compared to reduced water plots. Experimental
drought led to less fuel build-up, less native shrub cover, and more
invasive grass cover. The decreased biomass led to lower fire severity
indicated by smaller branch diameters and more terminal branches after
burning. Post-fire shrub cover was low in all plots, and lowest in added
and ambient plots compared to reduced water plots. There were fewer native
and more invasive species in post-fire droughted plots compared to
post-fire irrigated and ambient water plots. Our results demonstrate the
importance of fuel load to fire severity and plant community composition
on an ecosystem scale. Management strategies should focus on reducing fire
frequency to maintain the resilience of coastal sage scrub communities
facing drought. Control burns are not recommended for coastal sage scrub
communities because they will promote the growth of non-native plants.