Invasive grasses of North America

Grasses are one of the most abundant floras on all continents with the exception of Antarctica. Their divergence is estimated to be about 200 million years ago.cite journal |last=Wolfe |first=H. Kenneth |authorlink= |coauthors="et al." |year=1989 |month= |title=Date of the Monocot-Dicot Divergence Estimated from Chloroplast DNA Sequence Data |journal=PNAS |volume=86 |issue=16 |pages=6201–6205 |doi=10.2307/34294 |url= |accessdate= |quote= |doi_brokendate=2008-10-03 ] Humans have introduced these species both intentionally and unintentionally, through travel and trade, especially in North America. On the North American plains and prairies 11% of grasses are non-native.cite book |title=Principles of Conservation Biology |last=Groom |first=Martha J. |authorlink= |coauthors=Meffe, Gary K.; Carroll, C. Ronald |year=2006 |edition=3rd edition |publisher=Sinauer Associates |location=Sunderland, MA |isbn=0878935185 |pages= |url= ] It seems as if North America is a hotspot for many invasive grasses, which creates a major threat to all of the endangered grass species and a potential threat to other grass species in the surrounding areas. With conservation tactics or specific management policies humans can prevent invasive species from taking over and driving native North American plants to extinction.

Determining an invasive grass

In order for a non-native grass to become an invasive it has to have go through three processes. 1) The grass must have a pathway to be delivered to a new location. E.g. Boat, shoe, animal, etc. 2) The grass must be able to tolerate its new environment long enough to establish and reproduce. 3) The grass must be able to co-exist with the native plants. Invasive grasses are able to out compete native plants species by manipulating environmental conditions either through chemicals or other physiological factors such as genetics. These factors give an upper hand, which will allow the invader to out compete the native plants. For example, a study conducted in the Mojave desert by Smith "et al." in 2006, found that invasive grass species increase at higher concentrated carbon dioxide (CO₂) areas, especially in arid conditions which make up 20% of earth’s terrestrial surface area.cite journal |last=Smith |first=Stanley D. |authorlink= |coauthors="et al." |year=2000 |month= |title=Elevated CO₂ increases productivity and invasive species success in an arid ecosystem |journal=Nature |volume=408 |issue=6808 |pages=79–82 |doi=10.1038/35040544 |url=http://www.as.wvu.edu/biology/bio463/Smith%20et%20al%202000.pdf |accessdate= |quote= ] Therefore, the annual invasive grasses will out compete the native’s 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 is has a low burn rate, which makes it very susceptible to fire. As a result, it gives invasive grasses a head start in the reproduction process. Another invasive grass impact example, at the ecological level, is Cordgrass or more specifically Spartina anglica. This plant is native to the East coast of N. America and was introduced intentionally, to control erosion on the Pacific coast of North America. It now flourishes spreading across the mudflats of the Pacific coast changing them into salt marshes, which has tremendous effects on the fauna of the mudflats such as clams, worms, and anemones.cite journal |last=Thompson |first=John D. |authorlink= |coauthors= |year=1991 |month= |title=The Biology of an Invasive Plant: What makes "Spartina anglica" so successful? |journal=BioScience |volume=41 |issue=6 |pages=393–401 |doi=10.2307/1311746 |url= |accessdate= |quote= ]

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 elatius allowed the native grasses Danthonia californica and Festuca roemeri to flourish and out compete the non-natives.cite journal |last=Wison |first=Mark V. |authorlink= |coauthors=Clark, Deborah L. |year=2001 |month= |title=Controlling invasive Arrhenatherum elatius and Promoting Native Prairie Grasses through Mowing |journal=Applied vegetation Science |volume=4 |issue=1 |pages=129–138 |doi=10.2307/1479045 |url=http://oregonstate.edu/~wilsomar/PDF/WC_AVS_00.pdf |accessdate= |quote= |doi_brokendate=2008-10-03 ] 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 requires governmental assessment and policies to see that these pathways are blocked or regulated.

Conclusions

In this day and age it is almost impossible to prevent every non-native invasive grass into North America, but with the help of paid workers, volunteers, implementation plans, and tight regulations we will be able to control potential invaders. As for the invasive grasses that are already here, it is important to keep a strict control by implementing control strategies stated above. It is also important to use efficient yet effective methods so we can still maintain a large biodiversity of flora.

References

External links

* [http://marine.rutgers.edu/dmcs/ms309/Lec25/Lee02-TrEE-17-8-386.pdf Evolutionary Genetics of Invasive Species]
* [http://www.pnas.org/cgi/reprint/104/10/3883.pdf Increased genetic variation and evolutionary potential drive the success of an invasive grass]