A salamander perspective on earthworm invasions of north temperate forest ecosystem

Background/Question/Methods

Nonnative species invasions are a major component of global change.  In the eastern deciduous of forests of North America, nonnative earthworm invasions have been transforming the structure and function of forest floor environments and having complex effects on the plants and animals that depend on those environments.  Earthworms are an important prey to many predators including woodland salamanders, and prior research shows earthworm invasions drive spatial and temporal variation in salamander abundance and prey availability.  We used double-labeled leaf litter applied to forest 72 replicated plots with and without earthworms to measure how earthworm invasions altered the rates and total amounts of energy and nutrients that move from leaf litter to salamander populations.

Results/Conclusions

Red-backed salamanders (Plethodon cinereus) occupied 100% of the 72 study plots, and the number of salamanders uniquely marked during pre-monitoring ranged from 2-10 per plot.  All marked animals recovered over subsequent sampling years were recovered in the same plot where they were initially marked. Salamanders on all study plots were measurably enriched with label within 5 months.  Salamanders on earthworm invaded plots initially (5 mos) had higher amounts of label; however, the total amount of C and N label that moved into salamanders over four years was 80%-90% lower on earthworm-invaded plots compared to worm free plots. This was consistent with more rapid decomposition of leaf litter, dramatically reduced invertebrate abundance, and increased microbial activity on earthworm-invaded plots. Our research shows that despite being a potentially abundant food source, earthworms reduce the net amount of energy and nutrients that flow from forest leaf litter to support salamander populations and altering the effect of on energy flow and nutrient cycling in forest ecosystems.  There is likely little that can be done to eliminate earthworms from invaded forests, but actions to reduce the introduction of earthworms to new areas through the movement of bait and soils could protect remaining non-invaded forests.