Report written for:
The Edna Bailey Sussman Foundation
Caitlin M. Snyder
December 14, 2009
Non-native Earthworms as Agents of Forest Change in the Adirondack Park
Summary of proposed work
This project was undertaken in order to investigate nonnative earthworms as agents of
forest change in the Adirondack Park. My objectives were to first collect data on earthworm
species and their distributions; soil and litter characteristics; and plant and salamander
species assemblages on at least 20 sites across a pH gradient in the Adirondack Park. Second,
the land use history of sites would be compiled in order to assess the cultural and historical
aspects of the invasion. Land use history from existing records was proposed to be used to
determine probable earthworm dispersal methods (sources) and relationships between land
use and invasion. A report would then be provided to my host organization, the Adirondack
Park Invasive Plant Program (APIPP), and partner agencies such as the Adirondack Park
Agency and New York State Department of Environmental Conservation, detailing
earthworm distribution and species present. Finally, I planned to present an interactive
display about invasive earthworms for park visitors during APIPP’s Invasive Species
Awareness Week, July 5-11, 2009.
Narrative of work completed
Support provided by the Edna Bailey Sussman Foundation was used to conduct
research and educational outreach programs on nonnative earthworms throughout the
Adirondack Park, NY. Field work was completed over three watersheds, five counties, and
thirteen management areas within the Blue line from May through August, 2009.
Recreational fishing and boating locations were selected because they were assumed to be an
important contributor to the introduction and spread of earthworms, and also represent a key
part of the land use history within the Park. Sampling was conducted on earthworms, soil and
litter characteristics, and plant and salamander species assemblages at 44 popular fishing
access points and boat launches. Earthworms were sampled by randomly selecting at least
one 1ft2 plot on the forest edge per site (Photo 1). A biodegradable, efficient chemical
solution, consisting of a ground mustard seed and water, was applied to extract and collect
earthworms from the soil. In addition, forest floor characteristics were measured including
depth of the duff (leaves, twigs, and needles), percent cover of plants and corresponding
species, as well as soil pH and moisture. Salamanders were searched for within a larger,
surrounding plot by turning over any movable cover objects and looking on the forest floor.
A GPS location was taken at each site, and a sample site map was created (Figure 1).
Preliminary results
Of the 44 sites sampled across the Park, 37 were found to have at least one species of
earthworm present. The most common species encountered was Lumbricus rubellus, related
to the larger, common nightcrawler, and also sold as fishing bait. At least six different
species of earthworm were found in the Adirondacks in this study, across many ecological
groups and at varying densities. However, there are probably many more species
unaccounted for since most of the earthworms observed were juveniles and could not be
accurately identified to genus or species. Earthworms were placed into ecological groups
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according to their habits and characteristics: Epigeic species which dwell in the leaf litter and
are pigmented and often small (e.g. Dendrobaena sp); Endogeic species which dwell in
within the topsoil and are unpigmented and of varying sizes (e.g. Octolasion sp); Anecic
species which dwell deep in the soil and are pigmented and usually large in size (e.g.
Lumbricus terrestris, nightcrawler); Unidentified pigmented juveniles; and Unidentified
unpigmented juveniles (Figure 2). Densities were highly variable due to varying degrees of
recreational use and overall size of boat launches, but also probably depended on surrounding
vegetation, leaf litter layer composition, and soil texture, moisture, pH, and degree of
compaction, which were typically very different between the sites. Despite this variability, if
certain species assemblages (e.g. a high diversity or presence of each ecological group) and
high densities occur together both in time and space, then the forest floor could be negatively
impacted by physical and chemical disturbances (e.g. elimination of the duff layer) caused by
the action of nonnative earthworms.
Data obtained regarding plants and salamanders has yet to be correlated with
earthworm abundances and species assemblages. Salamanders were difficult to find around
the often highly disturbed boat launch sites. Only the red-backed salamander, a common
species in many types of woodland, was observed (Photo 2). Plants were variable among
sampling locations, and included tree species such as beech, birch, maple, hemlock, spruce,
and balsam fir. Herbaceous plants included blueberry, bunchberry, starflower, strawberry,
Canada mayflower, wild sarsaparilla, ferns, and grasses and weeds. In many cases more
sensitive plants such as trillium, pink lady’s slipper, false Solomon’s seal, rose-twisted stalk,
and bellwort were observed, possibly indicating that the earthworms in those sites were
having minimal disturbance to the forest floor.
Ms. Hilary Smith, director of APIPP, evaluated my work through biweekly meetings
where we discussed sites to sample and outreach opportunities for Invasive Species
Awareness Week (ISAW). For the educational component of my internship, I developed an
earthworm observatory in order to demonstrate the potential impacts of earthworms on soil
structure (Photo 3). During ISAW, July 5-11, 2009, I presented the earthworm observatories
along with an informational poster and brochures at the Adirondack Park Visitor Interpretive
Center in Newcomb, and at the Lake George Visitor’s Center in downtown Lake George.
These venues attract many visitors and work to inform the public about the unique biota of
the Park and current conservation issues. During the first day of ISAW, I traveled to down to
Lake George and worked an information booth about invasive species, including
earthworms, outside of the Visitor’s Center building (Photo 4). Throughout the week, nearly
1,270 visitors were recorded passing through the displays! The informational poster I made
will be displayed after ISAW at other venues on the ESF campus to help raise awareness
about the widely unknown impacts of earthworms on our natural ecosystems (Photo 5).
A summary report is currently being prepared for submission to APIPP, detailing
specifics such as the relationship between number of earthworms and variables including site
pH, leaf litter thickness, percent bare soil, and recreational activity. Using the collected data
from this summer, APIPP will be able to include nonnative earthworms in assessment of
habitat susceptibility to invasion from detrimental exotic plants such as garlic mustard, based
on research that indicates earthworms are a driving force behind plant invasion and
community change.
Discussion of future work
It is important to recognize that only recreational sites, often intensely used and
disturbed, were sampled and thus results are not representative of Adirondack forests as a
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whole. Nevertheless, this internship experience has helped provide insight into many of my
proposed questions, while also helping to develop additional questions for future research. In
addressing what the ecological and cultural factors affecting earthworms in the Adirondacks
are, I conclude that recreational areas such as fishing and boat access sites along lakes and
rivers are major proponents of earthworm introduction through disposed fishing bait, and
should become prevention targets. In addressing the current status of the invasion, I conclude
that earthworm populations may be in an early stage of invasion compared to most other
disturbed forests in New York. However, in order to keep the invasion and subsequent
impacts at a minimum, further work needs to be completed on how to reduce introduction of
earthworms at popular recreation sites. A recommended next step would be to look into the
dispersal of earthworms away from these introduction sites and into undisturbed areas of
Adirondack forests. It would be essential to know if earthworms are merely concentrated
around these fishing access sites, or if they have dispersed into nearby undisturbed forests.
Finally, in addressing the consequences of earthworm invasion, I support other
researcher’s hypotheses that earthworms in large numbers and diverse species assemblages
can potentially change Adirondack forests, but perhaps not to the extent to which they have
changed more deciduous, fertile, and higher pH ecosystems. Additional research, which I
hope to conduct next summer as part of my MS degree at SUNY ESF, should focus on
investigating the specific consequences of prey community and habitat changes for
bioindicator species, such as woodland salamanders, in order to more completely assess
changes in forest health and integrity across food webs from nonnative earthworms.
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Figure 1: Map of the 44
sites sampled during the
summer of 2009.
Figure 2: Number and type
of earthworms collected at
the 44 sites within the Park.
5
451
259
TOTAL
11
Anecic
22
Endogeic
96
Epigeic
70
Unidentified
unpigmented
juveniles
500
450
400
350
300
250
200
150
100
50
0
Unidentified
pigmented
juveniles
Number of individuals
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Photo 1: Earthworm plot
(center frame) and
vegetation plot at a
sampling site. (Photo by
C.M. Snyder)
Photo 2: An eastern redbacked salamander eyes an
earthworm. (Photo by C.M.
Snyder)
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Photo 3: An earthworm
observatory simulates the
soil structure in forests void
of earthworms (right)
versus invaded forests
(left). Observatories were
displayed at venues around
the Park during ISAW.
(Photo by C.M. Snyder)
Photo 4: Caitlin Snyder, recipient of a 2009
Sussman internship with APIPP, works an
earthworm information display during ISAW
at the Lake George Visitor’s Center. (Photo
by E. DeBolt)
Photo 5: Informational poster
created for ISAW (Photo by
C.M. Snyder)
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Acknowledgements:
Sincere thanks to the Edna Bailey Sussman Foundation for supporting this internship.
Without this funding, many ecological studies on smaller organisms like earthworms would
be overlooked, and their life histories and impacts left unknown. I’d also like to acknowledge
my host organization, APIPP, and Ms. Hilary Smith for helping to provide insight into my
field work and educational outreach this summer.