Fig. 1. Adult Amynthas worm found in leaf litter on the forest floor. They could be anywhere, and they are spreading everywhere.

Project Title: Earthworms: A Real Threat to Our Northeastern Sugarbushes

Investigators:

Bruce L. Parker1, Donald R. Tobi1 and Josef Gorres2

1. The University of VermontEntomology Research Laboratory661 Spear Street, Burlington, VT 05405‐0105bparker@uvm.edu , dtobi@uvm.edu Tel: 802:656-5440

2. The University of Vermont Plant and Soil Science Department258 Jeffords Hall, Burlington, VT 05405jgorres@uvm.edu

Project Summary/Abstract:

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. New particularly aggressive, more destructive East Asian earthworm species (genus Amynthas, a.k.a. Alabama Jumpers or Snake Worms) are colonizing our Northern forests (Fig. 1). In the past these worms were mainly observed in warmer Southern climates, where they are used as bait and compost worms. They have now spread to Vermont and other New England states. In areas where Amynthas has become established, the understory litter had disappeared and there was no sign of canopy tree species regeneration. A Shelburne VT sugar maple stand with a complete lack of understory plants was found to be infested with Amynthas worms in 201011 (Fig. 2). Little is known about the distribution of Amynthas worms, or their impact on sugar maple regeneration in Vermont and other northern states. We were recently notified that a proposal we submitted to the North American Maple Syrup Council (November 2014), also dealing with the abundance and distribution of exotic worms, was selected for funding. That project compliments work we propose herein. With funding from the Chittenden County Maple Sugarmakers we will be able to expand the scope of this research to better determine the current abundance and distribution of worm species in Northern sugarbushes relative to forest management practices, and assess their impact on understory diversity, maple regeneration and various soil characteristics.Project Objectives:

Long term goal: Gain 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:

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Fig. 2. Forest understory. The stand 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. Picture on right is Shelburne, Vermont sugarbush infested with Amynthas worms.

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 working 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.).

Expected Outcomes & Products: Data-based knowledge of the current status and threat of invasive earthworms (in particular, Amynthas sp.) to the long-term health and sustainability of sugarbushes in northern New England.

Scope of Work:

Limited studies have been conducted in Vermont and other nearby states on the occurrence of Amynthas worms in forests. Their distribution and abundance in sugarbushes is unknown, though there is observational evidence suggesting that they are present in some locations11. Little is known about the impact of Amynthas worms on sugarbush regeneration and general biodiversity of the forest understory. Worm sampling methods developed by the Univ. of Minnesota for the Great Lakes Worm Watch will be used.1

Obj. 1: Research plots will be established 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 our prior CCSMA-funded research studying the relationship between the occurrence of insects and diseases and sugarbush tree composition. This will enable us to use existing data on soil type and forest management practices in our analyses. Within 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 are established ~200 m apart within each plot. At each sub-plot, earthworm density will be determined in July when their abundance is highest, with a liquid extraction method.2 This uses a harmless solution of ground mustard and water, which is poured over a 1-sq ft area (Fig. 2). If worms are present, they will come to the soil surface within 2 minutes. Three sites per sub-plot will be selected for sampling annually. Worms will be collected, preserved in EtOH and keyed to species3. The abundance of worms by species, and the density and biomass of earthworms on an area basis will be determined.

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Obj. 2. Three 1 M2 vegetation-plots will be established at random within each sub-plot to assess understory vegetation, identifying and quantifying plants species within the square. Data will be analyzed to determine plant species richness, and correlated with worm biomass.4 The relationship between worm biomass and sugar maple regeneration will also be analyzed. 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 standard 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).Project Justification:

Earthworms are beneficial organisms that indicate healthy soil, Right? THINK AGAIN! We were brought up to believe that worms were good for our garden because they enhanced soil fertility and aerated the ground. Only recently have researchers discovered that worms have a Dark Side. 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 New aggressive, even more destructive East Asian earthworm invaders in the genus Amynthas (a.k.a. Alabama Jumpers or Snake Worms) are colonizing our forests.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 These worms have been found in soils of varied drainage classes, suggesting they can adapt to a variety of conditions. Görres & Melnichuk11 reported that in VT sites where they found Amynthas, the understory litter had disappeared and there was no sign of canopy tree regeneration. These worms were found in soils of varied drainage classes, suggesting they can adapt to a variety of conditions. 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 Emerald Ash Borer and the Asian Longhorn Beetle.12

Little is known about the distribution of Amynthas, or their impact on regeneration in Northern sugarbushes, though in the South, there is already evidence that these invasive earthworms are impacting forest biodiversity.8,9 Amynthas invasions have been observed 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

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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 Vermont sugarmakers have always been at the forefront of addressing these issues proactively. Based on evidence to the South, the invasion of the worms is upon us, and research is needed to obtain baseline information for the battle ahead.

Literature Cited:

1. Great Lakes Worm Watch. 2009. Worm Research Studies around the Nation. Univ. of Minnesota. http://www.nrri.umn.edu/worms/research/studies.html

2. Great Lakes Worm Watch. 2009. Sampling Earthworms. Univ. of Minnesota. http://www.nrri.umn.edu/worms/research/methods_worms.html

3. Great Lakes Worm Watch. 2009. Worm identification. http://www.nrri.umn.edu/worms/identification/index.html

4. Great Lakes Worm Watch. 2009. Sampling Plants. http://www.nrri.umn.edu/worms/research/methods_plants.html

5. Sampling Soils and Soil Characteristics. Univ. of Minnesota. http://www.nrri.umn.edu/worms/research/methods_soilscollect.html

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: 1637-1649.

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. Görres, J.H. & R.D.S. Melnichuk. 2012. Asian invasive earthworms of genus Amynthas in Vermont. No. Nat. 19(2): 313-322.

12. Wisconsin Department of Natural Resources. 2012. Little worms, big consequences. http://dnr.wi.gov/wnrmag/2012/12/worms.htm and http://dnr.wi.gov/topic/invasives/documents/classification/grf_crazy_worms.pdf

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.

Timeline:

This is a 3-year project, which 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. Base line data on plant biodiversity and soil characteristics will be collected during the early summer in Year 1, whereas worm collection will be done in late summer when populations are highest. Identification of the worms will be done as quickly as possible as they degrade over time in EtOH. Data analysis will take place during the winter after sampling has been completed. Worm collections will be made

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annually, and plant and soil sampling will be repeated as needed if changes to the forest floor are observed. Reports will be prepared for and presentations given as necessary at the annual meeting of the CCSMA.

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