Interactive effects of land use, grazing and environment on frogs in an agricultural landscape

Improved management of human-modified landscapes must be part of global efforts to combat biodiversity loss. We aimed to identify which land management types and environmental factors influenced the use of grazing landscapes by frogs. We surveyed frog assemblages in remnant vegetation, four different paddock types (pasture, linear planting, coarse woody debris addition and fence), and two grazing regimes (continuous and rotational). Frogs were surveyed using pitfall and funnel traps in twelve grazing farms in south-eastern Australia. We found that grazed agricultural landscapes provide important habitats for a variety of species of frogs and that frog assemblages were influenced by both farm management type and environmental variables, and their interactions. Total frog abundance increased with proximity to water more strongly in remnants compared to paddocks. This difference in response may be due to different traits and behaviours of frogs in remnants compared to frogs in open paddocks. Rare frog species richness and abundance of a common species (Limnodynastes tasmaniensis) increased with taller ground cover in remnants but no such relationship occurred in paddocks. Different types of predation risk in remnants compared to paddocks may result in greater ground cover shelter requirements in remnants, as vegetation structure can strongly influence predation. Total frog species richness increased more rapidly with higher rainfall in continuously grazed versus rotationally grazed farms. Higher rainfall was associated with taller ground cover. Continuously grazed farms had shorter average ground cover than rotationally grazed farms and the increased ground cover height associated with more rain may bring ground cover to a height better able to provide shelter and reduce desiccation risk for frogs. Our study highlights the importance of both land management practices and environmental conditions and their interaction in shaping frog assemblages. Improved frog biodiversity conservation may be achieved in grazing landscapes by retaining patches of remnant vegetation, maintaining water bodies such as farm dams, and maintaining tall ground cover within vegetation remnants.