California subalpine forest post-fire diversity and productivity

High severity fire may promote or reduce plant understory diversity in
forests. However, few empirical studies test long-standing theoretical
predictions that productivity may help to explain observed variation in
post-fire plant diversity. Support for the influence of productivity on
disturbance-diversity relationships is found predominantly in experimental
grasslands, while tests over large areas with natural disturbance and
productivity gradients are few and have yielded inconsistent results.
Here, we measured the response of post-fire understory plant diversity to
natural gradients of fire severity and productivity in a large-scale
observational study in California’s subalpine forests. We found that plant
species richness increased with increasing fire severity and that this
trend was stronger at high productivity. We used plant traits to
investigate whether release from competition might contribute to
increasing diversity and found that short-lived and far-dispersing species
benefited more from high severity fire than their long-lived and
near-dispersing counterparts. For far-dispersing species only, the benefit
from high severity fire was stronger in high productivity plots where
unburned species richness was lowest. Our results support theoretical
connections between fire severity, productivity and plant communities that
are key to predicting the consequences of increasing fire severity and
frequency on diversity in the coming decades.