Funded by the EPA STAR Program  
Grant no. R828902

Principle Investigator
v John C. Maerz, Ph.D.
v Bernd Blossey, Ph.D.
Ecology and Management of Invasive Plants Program
Department of Natural Resources                    
Cornell University

v James K. Liebherr, Ph.D.
Cornell University Insect Collection
Entomology Department
Cornell University

 v Victoria Nuzzo
Natural Areas Consultants

We are studying the potential impacts of non-native plant invasions on invertebrate communities and the  woodland salamanders that prey upon those invertebrates.  Few invertebrates feed on nonnative plants, so the replacement of native plant communities with nonnative plants might significantly reduce the quality or abundance of invertebrates available to salamanders as prey (Blossey 1999).  We hypothesize that invasions by nonnative plants are negatively affecting salamander fitness and abundance.  Specifically, we hypothesize that invertebrate quality and abundance is reduced in areas invaded by nonnative plants, and salamander populations in those areas show reduced foraging success, reduced growth, lower fecundity, lower, survival, and lower abundance.

We have five study sites in three different regions depending on the focal plant species.  We are studying garlic mustard (Alliaria petiolata) invasions in central New York, Japanese barberry (Berberis thunbergii) invasions in northeastern Pennsylvania, and Japanese stilt-grass (Microstegium vimineum) invasions in southeastern Pennsylvania.  Each site is a mature hardwood forest with an advancing plant invasion.  We use an array of 15 coverboard monitoring plots inside the invaded area, and an array of 15 plots in the non-invaded area.  Coverboard monitoring plots consist of 1 m X 1 m plots bounded by two 1 m long coverboards that are at least 5 m apart.  Arrays of plots in the invaded and non-invaded areas are often only 15-30 m apart on either side of an advancing “invasion front”.  The 1 m X 1 m plots are used to monitor vegetation and litter levels and decomposition.  In addition, we take samples of leaf litter from the perimeter of the plots to extract invertebrates.  Coverboards are searched every 2-3 weeks from April through October/early November, and all salamanders are captured, identified, measured, and marked uniquely using Visible Implant Elastomers (VIE).  Several times each year we use stomach flushing to monitor salamander diets for comparison with invertebrates from leaf litter samples and to determine how much food salamanders are getting in different habitats.

Click here to download salamander monitoring protocols

Link to Northwest Marine Tehcnologies, Inc. for more inforation on VIE’s

Our preliminary results show that salamander abundance varies greatly between invaded and non-invaded habitats, but the direction and magnitude of the change is not always the same.  Generally, it appears that salamander abundance declines, but on occasion, the abundance increases dramatically in invaded habitats.  The age/size distributions of salamanders also change between invaded and non-invaded areas.  We tend to find fewer juveniles and more adults in invaded areas, though female salamanders in invaded habitats are often significantly more fecund than females from non-invaded habitats.  The patterns of salamander abundance in invaded and non-invaded habitats appear to be driven by invasions of nonnative earthworms and their associated impacts on leaf litter decomposition and arthropod abundance.  Earthworms create an increase in food for adult salamanders, probably driving fecundity up (Maerz et al. unpublished manuscript).  However, earthworms are not available as prey to juvenile salamanders, particularly during the first two years of life.  Meanwhile, earthworms significantly erode the leaf litter and humus layers, driving the abundances of small arthropods down (Hendrix and Bohlen 2002).  These arthropods are the key food supply for juvenile salamanders, and are also important to adult salamanders during dry spells.  Therefore, earthworms probably drive the demographic changes in salamander populations.

There is a strong connection between earthworms, their impacts, and the invasions of the nonnative plants.  For all three plant species, we are finding earthworm abundance is significantly greater and leaf litter decomposition is significantly higher in the plant-invaded area than in the adjacent non-invaded area.  Other investigators have also noted the connection between the presence of nonnative plants and increased earthworm abundance or leaf litter loss (Kourtev et al. 1999, Meekins and McCarthy 2001).  Earthworms might be facilitating the invasions of nonnative plants into forests by increasing nutrient availability and reducing native plant abundance (Hendrix and Bohlen 2002).  Kourtev et al. (1999) hypothesize that there is a positive feedback between nonnative earthworms and nonnative plants, where earthworms initially facilitate plant invasions, and then nonnative plants have a positive effect on earthworm abundance through enrichment of leaf litter quality.  Under this scenario, it is the interaction between these two groups of nonnative invaders that is driving the changes in the forest food web and salamander populations.  Ultimately, our research is showing that plant invasions in forests occur in the context of many other invasions.  The impacts of other nonnative species might mask, offset, or enhance the impacts of focal nonnative species.  The interactive effects of multiple invasions are likely to be significantly larger and less predictable than the effects of a single invader, and focusing on the potential for interactive effects of multiple invasions will better illuminate current impacts on native communities and ecosystems.

 

 

 

 

 

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References

Blossey, B.  1999.  Before, during, and after: the need for long-term monitoring in invasive species management.  Biological Invasions 1:301-311.

Dean, W. R. J. 1998.  Space invaders:  modeling the distribution, impacts and control of alien organisms.  Trends in Ecology and Evolution 14:256-258.

Ehrenfeld, J. G., P. Kourtev, and W. Huang.  2001.  Changes in soil functions following invasions of exotic understory plants in deciduous forests.  Ecological Applications 11:1287-1300.

Hendrix, P. F. and P. J. Bohlen.  2002.  Exotic earthworm invasions in North America: ecological and policy implications.  BioScience 52:801-811.

Jaeger, R. G.  1978.  Plant climbing by salamanders: periodic availability of plant-dwelling prey.  Copeia 1978:686-691.

Kourtev, P. S., W. Z. Huang, and J. G. Ehrenfeld.  1999.  Differences in earthworm densities and nitrogen dynamics in soils under exotic and native plant species.  Biological Invasions 1:237-245.

Meekins, J. F. and B. C. McCarthy.  2001.  Effect of environmental variation on the invasive success of a non-indigenous forest herb.  Ecological Applications 11:1336-1348.

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