Effects of time since fire on frog occurrence are altered by isolation, vegetation and fire frequency gradients

Abstract

Aim: To quantify how frogs in terrestrial environments respond to recurrent fire, and to what extent this is mediated by isolation from breeding sites or vegetation structure.Location: Jervis Bay, south- eastern Australia.Methods: We used data from 8 years of pitfall trapping, collected via a random strati-fied design, to quantify frog occurrence at 110 locations. We then used an information theoretic approach to compare 13 logistic generalized linear mixed models, each of which related frog occurrence to a distinct combination of additive and interactive ef-fects of fire, vegetation structure and proximity to known breeding sites.Results: For all four species, the effect of one or more fire variables on frog occurrence depended on both the density of breeding sites in the surrounding area, or on the vegetation structure at the trap locality. A classic “fire averse” response of initial de-clines followed by post- fire recovery did occur, but only in frequently burned, low- quality terrestrial habitats (i.e., heath vegetation for Uperoleia tyleri, or locations with few available breeding sites for the remaining species), or in some cases, when suitable habitats were infrequently burned. However, a “fire- dependent” result of negative ef-fects of time since fire was also evident for some species and contexts.Main conclusions: The effect of fire on frog occurrence can be mediated by environ-ment. Therefore, a single species could be identified as either “fire dependent” or “fire averse” depending on the combination of isolation, vegetation types and fire histories in the study region. Failure to account for the context specificity of fire response curves could lead to incomplete conclusions regarding the effect of time since fire—or the cumulative impacts of multiple fires—on faunal assemblages.