Amphibians are currently considered one of the most threatened vertebrate groups. While numerous studies have addressed the causes of amphibian population decline, little is known about effects of invasive plants. Chinese tallow, Triadica sebifera, is an exotic deciduous tree that has invaded the southeastern United States. Amphibian larvae in environments invaded by Chinese tallow may be negatively impacted as autumn leaf litter decomposes in natal areas. In a previous controlled experiment, tallow leaf litter negatively impacted two anuran species that breed in winter, but not two species that breed in late-spring and summer. These results suggested that the impact of invasive Chinese tallow on anuran larvae may be dependent on when leaf litter enters aquatic habitats and when amphibians are present in the water which, in turn, may be influenced by local weather and climate change. The objectives of this study were to determine whether the timing of leaf fall from Chinese tallow and the timing of breeding of southern leopard frogs, Lithobates sphenocephalus influence survival of frog larvae, and identify water chemistry changes that may cause larvae mortality. Tadpoles were raised in five mesocosm treatments, each treatment with Chinese tallow leaf litter at different stages of decomposition. Tallow leaf litter was introduced into mesocosms approximately nine, seven, five, three, and one week before introduction of L. sphenocephalus larvae. Hence, treatments represented scenarios where weather influences amphibian breeding phenology and timing of aquatic decomposition of Chinese tallow leaf litter. Three water chemistry measurements, pH, salinity, and dissolved oxygen, were recorded for each mesocosm throughout the experiment.
Tadpole survival was significantly lower in treatments with shorter leaf decomposition times (three weeks and one week). Treatments also had significant differences in water chemistry. Dissolved oxygen levels were significantly lower in the treatments where larvae survival was low. Hence, hypoxic conditions were associated with recent leaf decomposition. Our results suggest that when larvae and Chinese tallow leaf litter enter aquatic habitats at similar times, anuran mortality may be high. If tallow leaf litter enters the water earlier than anuran larvae, dissolved oxygen levels may have time to return to levels that allow larvae to survive. These results demonstrate the importance of understanding how invasive plant species affect anuran larvae in the context of local weather and climate change.