The impact of two salamander species on detrital communities and forest ecosystem function

Amphibian populations are declining in many areas and amphibian extinctions are increasingly common. Because terrestrial salamanders reputedly impact forest floor ecosystem processes through predation, either population decline or species loss may affect those processes. The purpose of this study was to quantify top-down predatory impacts of salamanders in a forest floor ecosystem. In a hardwood mesic cove in northwestern, North Carolina, mesh-bottomed enclosures with forest floor soil and leaf litter were erected. Enclosures were populated with three Plethodon cinereus, two Plethodon montanus, both salamander species, or neither species. The invertebrate prey community was sampled by extraction and sifting of leaf litter. Mesh bags with cellulose discs were buried within each enclosure and periodically removed to measure decomposition rates. Additionally, salamanders were collected from adjacent sites in the field for gut content analysis. Large invertebrates such as predatory spiders and earthworms were observed in gut content analysis. In treatments excluding salamanders, oribatid mites decreased by 113% compared to treatments containing both salamanders. Likewise, total mite counts decreased by 125% and total collembola counts were 44.5% less in treatments where both salamanders were present (highlighted by a decrease of 31.3% in Sminthuridae). We found that salamanders did have an indirect top-down effect on microinvertebrates, potentially due to a release from macroinvertebrate predator pressure. While there was not a significant difference among treatments with respect to decomposition bag data, percent weight loss in treatments with both salamanders was greater on average than in treatments where salamanders were excluded. Our data supports the conclusion that salamanders do have an impact on forest floor communities by affecting trophic cascades.