Sequential Disturbance Effects of Hailstorm and Fire on Vegetation in a Mediterranean-Type Ecosystem

Abstract

Frequency and intensity of disturbance is projected to increase for many ecosystems globally, with uncertain consequences, particularly when disturbances occur in rapid succession. We quantified community response (52 shrub species and the tree Eucalyptus todtiana) to a severe hailstorm followed 2 months later by prescribed fire for a Mediterranean-type shrubland in southwestern Australia. Partial overlap of hailstorm path and fire perimeter provided a unique opportunity to compare storm and fire effects along a storm severity gradient (high–moderate–none) with and without fire. We quantified disturbance severity (bark and canopy removal, scorch height) and subsequent response (resprouting type, quantity and quality, and seedling regeneration) to evaluate evidence for disturbance interactions and implications for ecosystem recovery. Canopy loss, litter deposition, and tree bark removal increased significantly with hailstorm severity. Scorch heights in hailstorm + burn were significantly higher than fire alone, suggesting one disturbance conditioned the effect of the next. Hailstorm severity interacted with fire such that severely storm-affected shrubs and trees displayed reduced resprouting quantity and quality (length) after fire, implying resource depletion. Seedling regeneration was highest in fire-only plots for soil-stored seed species, while for serotinous species it was significantly reduced by the combination of storm and fire. Overall, our results show strong resilience of this Mediterranean-type ecosystem to storm or fire alone, whereas successive storm and fire reduced resprouting quantity and quality and selectively filtered recruitment of serotinous species, potentially altering species composition and structure. These results underscore the complex effects of linked and compound disturbances and reveal an important knowledge gap requiring future research.