Post-fire species composition and abundance of a lentic-breeding amphibian assemblage: case study of Ledson Marsh

Amphibians frequently inhabit wildfire-prone environments, but little is known how amphibians respond to fire. This study assessed the post-wildfire species composition and abundance of an amphibian assemblage in an 11.8-ha seasonal marsh. Pre-fire, four native amphibians occupied Ledson Marsh, including: California red-legged frog (Rana draytonii), Pacific treefrog (Pseudacris regilla), California newt (Taricha torosa), and roughskin newt (Taricha granulosa), in addition to the exotic American bullfrog (Rana [Lithobates] catesbeiana). Qualitative data revealed the California newt and Pacific treefrog were abundant species. In 2017, the Nuns Wildfire burned the majority of ground cover within the watershed. Nearly all marsh vegetation burned to charred and desiccated stubble. Renewal of substantial marsh vegetation occurred after one growing season, indicating a protected rootstock in a majority of perennial wetland plants. Post-fire, the same four native amphibians were still present. In addition, western toad (Anaxyrus boreas), a species previously undetected, also appeared. Appearance of western toad is consistent with its positive short-term response to fire, as described in other studies. The California newt and Pacific treefrog remained the two most abundant species post-fire. Over the short-term, the amphibian assemblage appeared resilient, or potentially benefitted, due to the temporary disturbance of wildfire within their lentic breeding habitat. The conclusion is based on the persistence of all pre-fire species, colonization by the western toad, and the return to an earlier successional stage, which may extend the longevity of the marsh. Since the rapid seasonal drying of habitat can increase the likelihood of fire under the current climate trajectory, we need a better understanding of the mechanisms that enable amphibians to cope with fire. This is particularly important over longer timelines and within wetland habitats that have the potential to burn.