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Exotic, Invasive Earthworms: A Clear and Present Danger to Regeneration in Our Northeastern Sugarbushes Bruce L. Parker & Margaret Skinner The University of Vermont, Entomology Research Laboratory 661 Spear Street, Burlington, VT 05405�0105 Contact Information: Tel: 802:656-5440

& Josef GÓ§rres The University of Vermont, Plant and Soil Science Department 258 Jeffords Hall, Burlington, VT 05405

This proposal addresses an emerging Maple Syrup industry issue: Management of exotic annelid worms, an invasive pest threating sugarbush forest health.

Executive Summary. Historically earthworms have been perceived as indigenous native organisms that enhance soil fertility. Few realize they are exotic species, some of which are invasive and represent a serious threat to sugarbush health. These worms are disrupting the natural biodiversity by transforming the forest floor structure and chemistry by rapidly consuming the understory

Fig. 1. Hatchling Amynthas worm found in soil. They could be anywhere, and they are spreading everywhere.

leaf litter layer which prevents maple regeneration and reduces the fertility and moisture-holding capacity of sugarbush soil. New, particularly aggressive, more destructive East Asian earthworm species (genus Amynthas, a.k.a. Alabama Jumpers or Snake Worms) are colonizing our forests and sugarbushes (Fig. 1). 9,10,11 In the past these worms were mainly observed in warmer Southern climates, where they are used as bait and compost worms. 9 They have now spread to Vermont and other New England states. In areas where Amynthas has become established, the leaf litter is gone within a few months, leaving bare soil and survival of maple seedlings is limited (Fig. 2). One of the first places where they have been noticed was in sugarbush in Shelburne, VT, where the reduced abundance 1

of understory plants was combined with a large number of squirming worms near the soil surface.11 They can reach densities of over 25 per square foot. Little is known about the distribution of Amynthas worms, or their impact on sugar maple regeneration in the northern states. This research will determine the current abundance and distribution of Amynthas worm species in northern New England sugarbushes and determine the relationship between worm density and several other factors, including forest management practices, coldhardiness zone and soil characteristics. The impact of these invasive worms on understory diversity and maple regeneration will also be assessed. Technical and Scientific Merit: Earthworms are beneficial organisms that indicate

Fig. 2. Forest understory, the one on the left has a wide variety of plants, including an abundance of maple regeneration and is worm free; the one on the right lacks regeneration or plant growth and is infested with worms. Images from Univ. of Minnesota Great Lakes Worm Watch.

healthy soil, Right? THINK AGAIN! We were brought up to believe that worms are good for our garden because they enhance soil fertility and aerate the ground. Only recently have researchers discovered that worms have a Dark Side.1 All earthworms in the forests of northern New England are exotic. Lumbricid earthworms were transported to the New World by European colonists. Though worms in our region are exotic, some species are also recognized as invasive, and these represent a serious threat to forest biodiversity by transforming forest floor structure and chemistry. 6,7,8,9 Görres & Melnichuk11 reported that in Vermont sites where they found Amynthas, the understory litter had disappeared and there was no sign of canopy tree regeneration. These aggressive Amynthas worms have been found in soils of varied drainage classes, suggesting they can adapt to a variety of conditions. There is no indication that cold winters significantly reduce their populations in subsequent seasons. Human activities such as fishing, gardening, hiking and “off roading” are primary means of dispersal.9 The threat to forest biodiversity is so serious that Wisconsin’s Dept. of Natural Resources placed Amynthas spp. on their list of prohibited species, along with more familiar forest pests like the


Asian Longhorn Beetle and Emerald Ash Borer.12 Before suitable management strategies can be developed, the extent of the problem must be evaluated. That is the objective of this project. Demonstrated Need. Based on the evidence from Southern regions, the impact of these invasive worms of the forest ecosystem can be significant. Given the impact of forests observed in other regions, it is likely the long-term health and sustainability of sugarbushes are being affected, and this will increase as their distribution expands.8,9 Amynthas invasions have been shown to reduce understory plant biodiversity and abundance and subsequently wildlife habitat. These earthworms reduce the forest undergrowth, rendering ground-dwelling birds more vulnerable to predation. In addition, nutrient cycling processes are altered by invasive earthworms which further change the forest community.13 Amynthas spp. change soil structure even more dramatically by replacing the upper soil and leaf litter with a thick layer of globular castings that appear to have deleterious effects on roots and mycorrhizal associations, critical to the health and well-being of maple trees. These worms are voracious feeders, consuming the annual litter layer so rapidly that none remains by the fall, which disrupts the moisture-holding and insulating potential of the forest floor. This has an obvious negative impact on mature maple trees during periods of drought and can reduce maple seedlings survival, a key process in sustaining sugarbushes. Several invasive pests have threatened the maple resource, and sugarmakers must take a proactive approach to these issues. Based on evidence to the South, the worm invasion is upon us, and research is needed to obtain baseline information for the battle ahead. Scope and Duration of the Project. This is a 3-yr project to be conducted in commercial sugarbushes to determine the presence of invasive worms relative to forest management practices. This will enable us to evaluate worm abundance and distribution over time. Year-to-year differences in weather are expected to influence worm populations once they are established at a site. Though there is observational evidence that these worms are present in hardwood forests, quantitative data on their distribution and abundance in sugarbushes is scarce11. Little is known about the impact of Amynthas worms on sugarbush regeneration and biodiversity of the forest understory. 3

Project Goals and Objectives: Long term goal. Gain a better understanding of the distribution, abundance, species diversity and impact of invasive exotic earthworms in sugarbushes in northern New England, from which strategies to combat them can be considered. Supporting objectives. 1. Determine the distribution, abundance and species diversity of invasive exotic earthworms in sugarbushes in northern New England relative to forest overstory and understory composition in sugarbushes across three coldhariness zones. 2. Assess the impact of Amynthas earthworms on sugar maple regeneration as a function of conditions at the forest floor (leaf litter depth, soil pH, etc.). 3. Identify current areas affected by Amynthas worms using a survey of sugarbush owners. Obj. 1. Research plots will be used at nine sites in active sugarbushes located in NH, VT, and NY, covering three USDA cold-hardiness zones (3, 4 and 5). These sites were established for a past project studying relationships between insects, diseases and tree composition. Use of these plots enables us to use existing data on soil type and forest management practices in our analyses. In each coldhardiness zone, there will be three sugarbushes, each with two plots: one comprising 90-100% sugar maple (Traditional sugarbush management), and the other managed for 25% non-sugar maple species (Ecological management). Four sub-plots have been established ~200 m apart in each plot. At each sub-plot, earthworm density will be determined in July when their abundance is highest, with a liquid extraction method developed by the Univ. of MN2. This uses a harmless solution of ground mustard and water, which is poured over a 1-sq ft area. If worms are present, they will come to the soil surface within 2 min. Three sites per sub-plot will be selected for sampling. Worms will be preserved in EtOH and keyed to species3. The abundance of worms by species, and density and biomass of earthworms on an area basis will be determined.


Obj. 2. Three 1-meter sq. vegetation plots will be established at random in each sub-plot, within which the understory vegetation will be identified and quantified. Several physical soil characteristics will be measured to further understand the impact of worms on the forest.5 Depth of the O and A horizons will be determined at three locations within each sub-plot using a soil corer (in worm-free soil the O horizon or litter layer is usually thick and the A horizon is absent or thin; the opposite occurs in worm-infested areas). Data will be analyzed to determine plant species richness and correlated with worm biomass and soil type and other characteristics.4 Obj. 3. We will prepare information on how to detect and id earthworms and share it with sugarmakers and add it to our website. Presentations will also be given at several regional sugarbush events. Sugarmakers will be asked to complete a short survey on the worm incidence in their sugarbushes. This will allow us to judge the extent of infestation in sugarbushes regionally. Expected Outcomes & Products: Data-based knowledge will be generated on the threat of invasive earthworms to the long-term health and sustainability of North American sugarbushes. Sugarmakers will gain an appreciation for how to minimize the spread of these invasive organisms. Application of Research to the Industry. Research will be conducted in commercial sugarbushes in NY, VT and NH, but results will be applicable throughout Northern New England, NY and PA and will be broadly publicized regionally and nationally. Articles will be prepared for the “Maple Syrup Digest�, and the PI will attend NAMSC meetings to report the findings. Best Practice Application. Scientists at UVM conform to best management practices as specified by the Department of Risk Management. Collaboration. Collaborators include growers, entomologists, foresters and a professional soil ecologist who has conducted research on worm bioecology over the past decade. In-kind/Partial Support and Potential for Continued Support. The senior scientists will contribute their time to the project, and UVM will contribute indirect costs. If this proposal is funded, we will submit complementary proposals to other Sugarmaker associations and USDA. 5

Literature Cited: 1. Great Lakes Worm Watch. 2009. Worm Research Studies around the Nation. Univ. of Minnesota. 2. Great Lakes Worm Watch. 2009. Sampling Earthworms. Univ. of Minnesota. 3. Great Lakes Worm Watch. 2009. Worm identification. 4. Great Lakes Worm Watch. 2009. Sampling Plants. 5. Sampling Soils and Soil Characteristics. Univ. of Minnesota. 6. Bohlen, P.J., S. Scheu, C.M. Hale, M.A. McLean, S. Migge, P.M. Groffman & D. Parkinson. 2004. Non-native invasive earthworms as agents of change in northern temperate forests. Front. in Ecol. & the Envir. 2:427-435. 7. Hale, C.M., L.E. Frelich & P.B. Reich. 2006. Changes in cold-temperate hardwood forest understory plant community in response to invasion by European earthworms. Ecology 87: 16371649. 8. Burtelow, A.E. P.J. Bohlen & P.M. Groffman. 1998. Influence of exotic earthworms on soil organic matter, microbial biomass and denitrification potential in forest soils of the northeastern United States. Appl. Soil Ecol. 9: 197-202. 9. Callaham, M.A., P. Hendrix & R.J. Phillips. 2003. Occurrence of an exotic earthworm (Amynthas agrestis) in undisturbed soils of the southern Appalachian Mts. USA. Pedobiologia 47: 466–470. 10. Bernard, M. J., M.A. Neatrour & T.S. McKay. 2009. Influence of soil buffering capacity on earthworm growth, survival, and community composition in the western Adirondacks and central New York. Nor. Nat. 16:269-284. 11. GÜrres, J.H. & R.D.S. Melnichuk. 2012. Asian invasive earthworms of genus Amynthas Kinberg in Vermont. No. Nat. 19: 313-322. 12. Wisconsin Department of Natural Resources. 2012. Little worms, big consequences. and 13. Snyder, B.A., M.A. Callaham & P.F. Hendrix. 2010. Spatial variability of an invasive earthworm (Amynthas agrestis) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mtn. Nat. Park. Biol. Inv. 13: 349-358.


Exotic, Invasive Earthworms: Clear and Present Danger to Regeneration in Our Northeastern Sugarbush  

Bruce L. Parker & Margaret Skinner, The University of Vermont, Entomology Research Laboratory Josef Gӧrres, The University of Vermont, Plant...

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