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Summary

nutrient cycles in temperate or temperate/coniferous forests. These earthworms increase the cycling and leaching of nutrients by breaking up decaying organic matter and spreading it into the soil. Since these northern forests rely on thick layers of decaying organic matter for growth and nutrition, they are diminishing in diversity and young plants struggle in these envirnments. Many species of trees and other plants may be incapable of surviving such drastic changes in available nutrients (Cambell, 2009).This change in the plant diversity directly affects the other organisms of the envirnment and often leads to increased invasions of other exotic species as well as overall temperate forest

decline.

File:Temperate and boreal forests''', Biol Invasions (2006) 8:1235–1245 (2006)

Invasive Earthworms

nutrient cycles

(Cambell, 2009). By redistributing nutrients, mixing soil layers, and creating pores in the soil, they can drastically effect the characteristics of the soil important to the rest of the ecosystem. In addition, earthworms break up decomposing matter on the surface of the soil and carry or mix it into the surrounding soil often carrying some of the nutrients deeper into the soil (Bohlen, 2004). The earthworms are migrating north into forests and are believed to be primarily destroying forests between 45^o and 60^o latitude in North America (Frelich, 2006).

Influence on Nutrient cycles

Most northern forests rely on a thick layer of decomposing organic matter as their primary nutrient source (Cambell, 2009). These nutrients, carbon, phosphorus, and nitrogen, are necessary for the production of many components of the cells, making it a limiting factor often in growth and maturation. When organisms die, their bodies slowly decompose forming a layer of nutrients on the forest floor (Hendrix, 2006). This provides for the growth of the trees, ferns, and smaller ground plants. When earthworms are introduced into areas where they previously didn't reside, the earthworms breakup the organic layer. They often mix the nutrients into the soil where they become leached and unavailable to most species of plants. WIthout this important source of nutrients, many species of plants cannot survive.
Carbon, nitrogen, and phospherous are necessary components of different cellular products, including

protiens (Cambell, 2009).The primary carbon source for forests is located in the decomposing organic matter found on the surface of the forest floor, and this also is a large source of nitrogen and phosphorus. When earthworms invade forest soil they break up this layer of organic material. This is the mechanism in which the nutrients become unavailable. Once the organic material is broken up, nitrogen, phospherous, and carbon can be leached into the soil. This leads to increased mineralization and loss of nutrients. Overall effects include: a decrease in the thickness of the organic layer, increased bulk density, spreading of the organic matter and humus, and increased rate of decomposition

(Bohlen, 2004), (Eisenhauer et al. 2007), (Frelich, 2006). These envirnmental alterations (drier, brighter, nutrient deficient soil) cause the community wildlife diversity to decrease and it generally creates a more simple ecosystem.

Effects on Organisms

When many of the species cannot survive, the diversity of the forest decreases drastically. Without the nutrients available, some species are completely erraticated which provide important biological

betula, and maples suffer greatly in the changing habitats, as well as many forest herbs like aralia, viola,and botrychium

. These plants are commonly eradicated from the temperate forests after only months of the invasive's presence. Also, since a decrease in overall groundcover and canopy vegatation is witnessed, food for other organisms becomes scarce (Cambell, 2009). With this implication, some organisms are forced to leave the areas, and the few plants remaining are often eaten shortly after germination.

These invasive earthworms destroy the native species habitat and many species suffer besides plants since their available food and shelter becomes greatly limited. As stated above, often animals are forced to leave or starve due to decreased overall vegetation. With decreased ground level vegetation, many terrestrial organisms like insects, small mammals, and other vertebrates must compete for less resources, leading to decreased diversity and population (Szlavecz et al. 2006). In addition, the native species of worms have to compete with the invasives, which they often can't since their envirnment changes to drastically. Many of these worms die since they are not well adapted to the new conditions of the forest soil (Hendrix, 2006).

Generally, the addition of earthworms to a forest a clear decrease in diversity is observed, and often other exotic species follow that can survive the nutrient diminished envirnment better than the natives. For example, in newly invaded forests

garlic mustard

, invasive species, make drastic increases in population density (Frelich, 2006), (Szlavecz et al. 2006). To summarize, we see a decrease in diversity, seedlings population, organic matter volume, and overall habitat. In addition, we see increased invasive species often, and decreased diversity of non-plant organisms.

Origins

Most of the harmful invasive earthworms are European or Asian and came over in soil during the 1700s but our own recreational practices and construction methodes are the primary mode of transportation for the earthworms now (Frelich, 2006). Their movement in the soil is quite slow on their own, but with human transportation their migration drastically increases. The earthworms are commonly used as bait for fishing, and many escape or are released. This is a very common way in which they move into new locations. In addition, many are moved physically in soil through construction practices. Either they can be moved in dirt loads from one location to another, or be trapped in dirt attached to wheels of larger trucks (Eisenhauer et al. 2007). Some propose a major mode of transportation is through logging trucks which move from location to location with large amounts of dirt attached to their wheels.

Solutions

At this point there is no known way to remove the earthworms from the soil where they are destroying forests but simple methods may help us slow the migration and destruction of our forests (Frelich, 2006). One way to help reduce their migration would be to reduce the number of worms released during fishing practices. This seems harmless to many, but releasing them increases the number of available mates for the worms assisting their proliferation and migration efforts. In addition, large trucks participating in logging and consturction should wash their vechicles often, and remove dirt from their wheel treds before arriving in new forest areas. Ideally, the movement of dirt from one location to the other could regulated so that dirt from areas with earthworms commonly isn't moved into forests without the invasive species. This is a logical step for many different species of invasives found in dirt, but is nearly impossible to regulate (Eisenhauer et al. 2007). All in all, it would take years to restore an area of forest, even if the worms could be removed (Eisenhauer et al. 2007),(Frelich, 2006). Allowing seedlings, native species, and previous nutrient conditions to stabalize would take a great deal of time and effort. Restoring forests to their natural state will be a challenge for future generations to study and perfect considering ~50% of our terrestrial carbon pool is incorporated into forests, and the benefit forests provide in the oxygen cycle.

Future experiments are examening evidence that certain characteristics of the soil habitat could have a great effect on the ability of te earthworms to invade an envirnment. High salinity, sandy soils have been shown to have increased resistance to these invasive earthworms (Frelich, 2006). Additionally, low pH and high carbon to nitrogen ratio plant material may assist in resistance of forest ecosystems to invasive earthworms. Alternatively, high pH, and low C:N ratios appear to be more susseptible. These envirnmental factors may be points of interest when designing procedures or protocols to protect forests and destroy the invasive earthworms before they destroy the northern forests.

References

(1) Blakemore, R. J. American Earthworms from North of the Rio Grande- a Species Checklist. Rep. Yokohama, Japan: YNU, 2006.
(2) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson Benjamin Cummings, 2009.
(3) Bohlen, Patrick J., and Peter M. Groffman. "Influence of Earthworm Invasion on Redistribution and Retention of Soil Carbon and Nitrogen in Northern Temperate Forest." Ecosytems 7 (2004): 13-27.
(4) Eisenhauer, Nico, Stephan Partsch, Dennis Parkinson, and Stefan Scheu. "Invasion of a deciduous forest by earthworms: changes in soil chemistry, microflora, microarthropds, and vegetation." Soil Biology and Biochemistry 39 (2007): 1099-110.
(5) Frelich, Lee E., Cindy M. Hale, and Stefan Scheu. "Earthworm invasion into previously earthworm-free temperate and boreal forests." Biological Invasions 8 (2006): 1235-245. Print.
(6) Hendrix, P. F., G. H. Baker, and M. A. Callaham Jr. "Invasion of exotic earthworms into ecosystems inhabited by native earthworms." Biological Invasions 8 (2006): 1287-300.
(7) Szlavecz, Katalin, Sarah A. Placella, and Richard V. Pouyat. "Invasive earthworm species and nitrogen cycling in remnant forest patches." Applied Soil Ecology 32 (2006): 54-62.