Bernadette Williams Wisconsin DNR Forestry Division
Pioneers in the colonization and preparation of the land, they pre-date the invasion by fungi, land plants, insects (400 to 500 million years), dinosaurs and mammals (200 million years), and hominids (4 million years). They are ubiquitous in all but the driest of regions and the present day world distribution of roughly 7000 species in 18 families.
Earthworm Functional Groups
epigeic - litter dweller
endogeic - topsoil dweller
anecic - subsoil dweller
Earthworms are promiscuous, polygamous, hermaphrodites but some can reproduce parthenogenetically.
Worms eat dirt. They are detritivorous where they
feed on decaying organic matter (leaf litter) and geophageous (dirt) and feed mainly in the soil layers.
A layer of dark, fertile humus made of rotting plants lies at the soil’s surface. Underneath, the topsoil contains plant roots, and plant and animal remains that bacteria and fungi are helping to rot down. The subsoil contains fewer plant and animal remains but has plenty of minerals washed down from the layers above. Below are rock fragments, then solid bedrock.
Changes to the Soil Environment
Influence the physical, chemical, and biological properties of the soil through: • Burrowing • Casting • Feeding • Mucus secretion Death/decomposition
The effects of the above depends on the functional group of earthworms.
Changes to the Soils Physical and Biological Properties
Physical
• Mixing of the soil profile • Incorporation of organic
materials • Water infiltration & holding capacity • Soil aeration • Soil erosion • Soil structure & aggregate formation Biological • Micro-organisms • Nematodes • Food source for birds and
mammals • Plant productivity
Earthworms in Sugar Maple Forests
• Loss of the duff layer is the most important impact in sugar maple forests
• Earthworm droppings
denser than the native soils compacting the forest floor rather than aerate it.
• Research shows degraded root structures and fewer sugar maples in forests infested with earthworms. (*slight variation depending on worm species and functional group)
Healthy vs. Unhealthy Forest Floor and Soil.
Earthworms have considerable capacity to change the nature of their environment to suit their survival. Ecological requirements (moisture, temperature, and food supply) greatly influence the rates of reproduction and growth.
Healthy, undisturbed forests are typically dynamic ecosystems anchored in a complex soil structure that teems with macro- and microscopic life and the key to health in our state’s forest resides in a rich fungal based soil that slowly decomposes its organic matter.
There is a nutrient balance between the vegetation above ground and below the leaf litter on the forest floor. When a forest becomes heavily infested with earthworms the leaf litter is depleted and the soil is now vulnerable to invasive species which in turn causes a decrease in the diversity of native plants and animals.
Earthworm Invasion
Dispersal
• Source Population • Human Activity • Natural Expansion
• Forest Edges • Rivers Streams
Resource Quantity • Plant Productivity
• Soil & Organic Matter
Physical Effects • Burrowing & Casting • Loss of Leaf Litter • Soil Aggregates
• Porosity • Hydrology • Erosion
Resource Quality • Vegetation Type • Litter C&N Ratio
• Tannins, Polyphenotics Soil Factors
• Moisture Hydrology • Texture, Sand/Silt/Clay
• Acidity
Geochemical Effects • Mixing Soil Layers
• Mineral Weathering • Change of Mineralogy
Biological Effects • Change in Soil Habitat • Faster Nutrient Cycling • Less Fungally Dominated
• Fewer Mycorrhizae • Change in Rooting Zone
• Altered Seedbed
Ecological Consequences
Ecosystem Properties • Carbon Loss (short term) • Carbon Stabilization (long term) • Nitrogen Retention? • TREE NUTRITION • TREE REGENERATION
Ecological Communities • Invasive Plant Invasions • Loss of Native Plant Communities • Soil Invertebrate Community Shifts • Microbial Community Shifts
Predation Earthworms have many, many predators (eg. Bears, foxes, moles, birds, snakes,
frogs, fishes, insects, ants, leeches, planarian flatworms, and even a few cannibalistic earthworms; in addition parasites (eg. Flies, helminthes, nematodes, protozoans,
bacteria, and viruses).
Hunger, W. Sevenoh
What YOU Can Do to HELP!
While we don’t have a way of ridding the forests of worms once they are established, we can keep them from spreading to forests that are not yet invaded.
• Don’t release live bait on land or in the water
• Dispose of live worms in the trash.
• Avoid introducing worms and their eggs
(vermicomposting) to native landscapes. Earthworm-free areas still exist.
• Wash your shoes and tire treads.
SPREAD THE WORD CONTAIN YOUR CRAWLERS!
Keep Worms out of Wisconsin’s Woods!
FOR MORE INFORMATION: dnr.wi.gov SEARCHinvasives
