Invasive grasses of North America
Encyclopedia
Grasses are one of the most abundant floras on all continents except Antarctica. Their divergence
is estimated to have taken place 200 million years ago. Humans have intentionally and unintentionally introduced these species to North America
through travel and trade. On the North American plains, prairie
s, grassland
s, and meadow
s at least 11% of grasses are non-native. North America is considered a hotspot for many invasive plant species of grasses, which threatens all of the endangered native grass species and potentially threatens other grass species. Conservation tactics and management policies can help prevent invasive species
from taking over and driving native North American plants to extinction.
These factors give an upper hand, which will allow the invader to outcompete the native plants. For example, a study conducted in the Mojave desert
of California
by Smith et al. in 2006, found that invasive grass species increase in areas with higher concentrations of carbon dioxide
(CO2), especially in arid conditions which make up 20% of Earth’s terrestrial surface area. Therefore, the annual invasive grasses will outcompete the natives because they use CO2 to their advantage.
in the reproduction process. Another invasive grass impact example, at the ecological level, is Cordgrass
or more specifically Spartina anglica
. This species arose in England as an allotetraploid of two wild species and was introduced intentionally, to control erosion on the coasts of North America. It now flourishes spreading across the mudflats of the Pacific coast changing them into salt marsh
es, which has tremendous effects on the fauna of the mudflats such as clams, worms, and anemones.
allowed the native grasses Danthonia californica
and Festuca roemeri to flourish and out compete the non-natives. This is an effective method for the control of invasive grasses but it will take many hours of hard manual labor, which could be costly. Using chemicals is an effective way to control non-natives but it is not very ecologically friendly. Chemicals such as herbicides can contaminate waterways or kill other plants in the immediate area. Biological control is the use of other organism to reduce the invader grass. This has been proven to be effective but has also ricocheted back in a negative way. Other options include using multiple approaches at the same time, for example, mowing a specific region of grass land and then using an herbicide to target the invasive. The ultimate way to control invasive grasses in North America is to prevent them from entering in the first place. The first step of this prevention is identifying and regulating the grasses' pathway. After that it needs government assessment and policies to see that these pathways are blocked or regulated.
Genetic divergence
Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes through time, often after the populations have become reproductively isolated for some period of time...
is estimated to have taken place 200 million years ago. Humans have intentionally and unintentionally introduced these species to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
through travel and trade. On the North American plains, prairie
Prairie
Prairies are considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type...
s, grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s, and meadow
Meadow
A meadow is a field vegetated primarily by grass and other non-woody plants . The term is from Old English mædwe. In agriculture a meadow is grassland which is not grazed by domestic livestock but rather allowed to grow unchecked in order to make hay...
s at least 11% of grasses are non-native. North America is considered a hotspot for many invasive plant species of grasses, which threatens all of the endangered native grass species and potentially threatens other grass species. Conservation tactics and management policies can help prevent invasive species
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....
from taking over and driving native North American plants to extinction.
Attributes
Non-native grasses are classified as invasive if they have the following three attributes:- The grass must have a pathway to be delivered to a new location, e.g. boat, shoe, animal, vehicle, feed, contaminated seed, etc.
- It is able to tolerate its new environment long enough to establish and reproduce.
- It is able to co-exist with native plants. Invasive grasses can outcompete native plants species by manipulating environmental conditions through either chemicals or other physiological factors.
These factors give an upper hand, which will allow the invader to outcompete the native plants. For example, a study conducted in the Mojave desert
Mojave Desert
The Mojave Desert occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, southwestern Utah and northwestern Arizona, in the United States...
of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
by Smith et al. in 2006, found that invasive grass species increase in areas with higher concentrations of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2), especially in arid conditions which make up 20% of Earth’s terrestrial surface area. Therefore, the annual invasive grasses will outcompete the natives because they use CO2 to their advantage.
Impacts
There are many impacts involving invasive grasses in North America, which range from an ecosystem level to a community level to a genetic level. Such impacts influence habitat structure, disturbance regimes, and nutrient cycling. A successful invasion of a grass may result in new hybrid species, which can have both good and bad results. A good result could be a new species. A bad result could produce a sterile species, which would eventually lead to the extinction of that grass. European Cheatgrass invading the North American prairies is an example of a disturbance regime because it burns quickly and is very susceptible to fire. As a result, it gives invasive grasses a head startHead start (positioning)
In positioning, a head start is a start in advance of the starting position of others in competition, or simply toward the finish line or desired outcome...
in the reproduction process. Another invasive grass impact example, at the ecological level, is Cordgrass
Cordgrass
Spartina, commonly known as cordgrass or cord-grass, is a genus of 14 species of grasses in the family Poaceae. They are native to the coasts of the Atlantic Ocean in western and southern Europe, northwest and southern Africa, the Americas and the southern Atlantic Ocean islands; one or two species...
or more specifically Spartina anglica
Spartina anglica
Spartina anglica is a species of cordgrass that originated in southern England in about 1870. It is an allotetraploid species derived from the hybrid Spartina × townsendii, which arose when the European native cordgrass Spartina maritima hybridised with the introduced American Spartina...
. This species arose in England as an allotetraploid of two wild species and was introduced intentionally, to control erosion on the coasts of North America. It now flourishes spreading across the mudflats of the Pacific coast changing them into salt marsh
Salt marsh
A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh...
es, which has tremendous effects on the fauna of the mudflats such as clams, worms, and anemones.
Management
In order to keep North American native grasses from potentially going extinct from invasive grasses, it is important to control or better yet prevent such invasions in the first place. There are many ways to go about this such as controlling species mechanically or physically. This includes hand removal of grasses or by machine. In a five-year study conducted by Wilson et al. (2001) in Western Oregon, showed that mowing prairies of the invasive grass Arrhenatherum elatiusArrhenatherum elatius
-Introduction:Arrhenatherum elatius, with the common names false oat-grass, tall oat-grass, tall meadow oat, onion couch and tuber oat-grass, is a perennial species of grass, common in the temperate regions of Europe....
allowed the native grasses Danthonia californica
Danthonia californica
Danthonia californica is a species of grass known by the common name California oatgrass. This plant is native to two separate regions of the Americas, western North America from California to Saskatchewan, and Chile.-Description:...
and Festuca roemeri to flourish and out compete the non-natives. This is an effective method for the control of invasive grasses but it will take many hours of hard manual labor, which could be costly. Using chemicals is an effective way to control non-natives but it is not very ecologically friendly. Chemicals such as herbicides can contaminate waterways or kill other plants in the immediate area. Biological control is the use of other organism to reduce the invader grass. This has been proven to be effective but has also ricocheted back in a negative way. Other options include using multiple approaches at the same time, for example, mowing a specific region of grass land and then using an herbicide to target the invasive. The ultimate way to control invasive grasses in North America is to prevent them from entering in the first place. The first step of this prevention is identifying and regulating the grasses' pathway. After that it needs government assessment and policies to see that these pathways are blocked or regulated.