Invasive earthworms of North America
Encyclopedia
Invasive species
of earthworms, specifically from the suborder Lumbricina, are migrating and spreading through North America. Their introduction is having drastic effects on the multiple 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 environments. 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 environment and often leads to increased invasions of other exotic species as well as overall temperate forest
decline.
, since they alter many different variables of their ecosystem drastically since they are detritivores (Frelich, 2006). Of the 182 taxa of earthworms found in the United States of America and Canada, 60 or almost 33% are invasive species (Blakemore, 2006). Specifically, Lumbricus terrestris, rubellus, friendi, and Dendrobaena octaedra have been studied for their ability to invade previously uninhabited locations and disturb the local ecosystems (Blakemore, 2006), (Frelich, 2006). These earthworm species are primarily from Europe and Asia, and they are disturbing many 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 45o and 60o latitude in North America (Frelich, 2006).
as their primary nutrient source (Campbell, 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 phosphorus are necessary components of different cellular products, including carbohydrates, ribonucleases, and proteins (Campbell, 2009).The primary carbon source for forests is CO2 from the atmosphere. However, all other nutrients are taken up by trees and plant from the soil. These nutrients are replenished from the decomposing organic matter on the surface of the forest floor. 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, phosphorus, 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 environmental alterations (drier, brighter, nutrient deficient soil) cause the community wildlife diversity to decrease and it generally creates a more simple ecosystem.
s to the ecosystem
. In addition, young plants rarely can grow without that available nitrogen source nearby (Bohlen, 2004). Since young plants do not have the elongated root systems that older trees have, they often cannot attain enough nutrients to survive (Eisenhauer et al. 2007). Thus, few saplings or under-canopy plants grow to full maturity and generally only the larger trees with extensive root systems survive. The addition of earthworms to an environment has been shown to decrease mycorrhizae associations with roots. This adds to the problem of finding available nutrients for plants (Frelich, 2006). Specifically, trees like populus, 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 ground cover and canopy vegetation 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 environment 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 environment better than the natives. For example, in newly invaded forests buckthorn
and 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.
and migration efforts. In addition, large trucks participating in logging and construction should wash their vehicles often, and remove dirt from their wheel treads before arriving in new forest areas. Ideally, the movement of dirt from one location to the other could be regulated so that dirt from areas where earthworms are common is not 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 stabilize 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 examining evidence that certain characteristics of the soil habitat could have a great effect on the ability of the earthworms to invade an environment. High salinity and 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 susceptible. These environmental 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. Another possible solution would be the introduction of the New Zealand Flatworm (Arthurdendyus triangulatus) which is invasive to Europe and is in the process of wiping out the earthworms native there. As those earthworms native to Europe are invasive here it is most interesting as to why this has yet to be suggested as a biological control, which is a task it is well suited for.
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
of earthworms, specifically from the suborder Lumbricina, are migrating and spreading through North America. Their introduction is having drastic effects on the multiple nutrient cycles in temperate or temperate-coniferous forests. These earthworms increase the cycling and leaching
Leaching
In general, leaching is the extraction of certain materials from a carrier into a liquid . Specifically, it may refer to:...
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 environments. 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 environment and often leads to increased invasions of other exotic species as well as overall temperate forest
Temperate forest
Temperate forests correspond to forest concentrations formed in the northern hemisphere. Main characteristics include: wide leaves, big and tall trees and non seasonal vegetation...
decline.
Invasive earthworms
Earthworms are from the suborder Lumbricina, and are primarily engineers of their environment. Earthworms are considered keystone speciesKeystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
, since they alter many different variables of their ecosystem drastically since they are detritivores (Frelich, 2006). Of the 182 taxa of earthworms found in the United States of America and Canada, 60 or almost 33% are invasive species (Blakemore, 2006). Specifically, Lumbricus terrestris, rubellus, friendi, and Dendrobaena octaedra have been studied for their ability to invade previously uninhabited locations and disturb the local ecosystems (Blakemore, 2006), (Frelich, 2006). These earthworm species are primarily from Europe and Asia, and they are disturbing many 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 45o and 60o latitude in North America (Frelich, 2006).
Influence on nutrient cycles
Most northern forests rely on a thick layer of decomposing organic matterOrganic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...
as their primary nutrient source (Campbell, 2009). These nutrients, carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, 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
Leaching (agriculture)
In agriculture, leaching refers to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planting, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss.Leaching may also refer to ...
and unavailable to most species of plants. Without this important source of nutrients, many species of plants cannot survive.
Carbon, nitrogen, and phosphorus are necessary components of different cellular products, including carbohydrates, ribonucleases, and proteins (Campbell, 2009).The primary carbon source for forests is CO2 from the atmosphere. However, all other nutrients are taken up by trees and plant from the soil. These nutrients are replenished from the decomposing organic matter on the surface of the forest floor. 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, phosphorus, and carbon can be leached into the soil. This leads to increased mineralization
Mineralization
Mineralization may refer to:* Mineralization , the process through which an organic substance becomes impregnated by inorganic substances...
and loss of nutrients. Overall effects include: a decrease in the thickness of the organic layer, increased bulk density
Bulk density
Bulk density is a property of powders, granules and other "divided" solids, especially used in reference to mineral components , chemical substances, ingredients, foodstuff or any other masses of corpuscular or particulate matter. It is defined as the mass of many particles of the material...
, spreading of the organic matter and humus, and increased rate of decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
(Bohlen, 2004), (Eisenhauer et al. 2007), (Frelich, 2006). These environmental 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 eradicated which provide important biological nicheEcological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s to the ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
. In addition, young plants rarely can grow without that available nitrogen source nearby (Bohlen, 2004). Since young plants do not have the elongated root systems that older trees have, they often cannot attain enough nutrients to survive (Eisenhauer et al. 2007). Thus, few saplings or under-canopy plants grow to full maturity and generally only the larger trees with extensive root systems survive. The addition of earthworms to an environment has been shown to decrease mycorrhizae associations with roots. This adds to the problem of finding available nutrients for plants (Frelich, 2006). Specifically, trees like populus, betula, and maples
Maples
-People:* Chauncy Maples , British Anglican missionary and bishop in Africa* John Maples, Baron Maples , British politician* Marla Maples , American actress, former wife of Donald Trump...
suffer greatly in the changing habitats, as well as many forest herbs like aralia
Aralia
Aralia , or Spikenard, is a genus of the plant family Araliaceae, consisting of 68 accepted species of deciduous or evergreen trees, shrubs, and rhizomatous herbaceous perennials. The genus is native to Asia and the Americas, with most species occurring in mountain woodlands...
, viola
Viola
The viola is a bowed string instrument. It is the middle voice of the violin family, between the violin and the cello.- Form :The viola is similar in material and construction to the violin. A full-size viola's body is between and longer than the body of a full-size violin , with an average...
,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 ground cover and canopy vegetation 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 environment 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 environment better than the natives. For example, in newly invaded forests buckthorn
Buckthorn
The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...
and garlic mustard
Garlic Mustard
Garlic mustard is a biennial flowering plant in the Mustard family, Brassicaceae. It is native to Europe, western and central Asia, and northwestern Africa, from Morocco, Iberia and the British Isles, north to northern Scandinavia, and east to northern India and western China...
, 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 18th century but our own recreational practices and construction methods 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 proliferationProliferation
Proliferation may refer to:*Nuclear proliferation*Chemical weapon proliferation*Cell proliferation* The proliferative phase of wound healing...
and migration efforts. In addition, large trucks participating in logging and construction should wash their vehicles often, and remove dirt from their wheel treads before arriving in new forest areas. Ideally, the movement of dirt from one location to the other could be regulated so that dirt from areas where earthworms are common is not 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 stabilize 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
Oxygen cycle
The Oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within its three main reservoirs: the atmosphere , the total content of biological matter within the biosphere , and the lithosphere...
.
Future experiments are examining evidence that certain characteristics of the soil habitat could have a great effect on the ability of the earthworms to invade an environment. High salinity and 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 susceptible. These environmental 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. Another possible solution would be the introduction of the New Zealand Flatworm (Arthurdendyus triangulatus) which is invasive to Europe and is in the process of wiping out the earthworms native there. As those earthworms native to Europe are invasive here it is most interesting as to why this has yet to be suggested as a biological control, which is a task it is well suited for.