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My 2010 Young Naturalist Award Essay (Finalist)
Washington International School, Washington D.C.
Introduction
My study asks the general question: can a natural ecosystem be restored in a place over-run with Non-Native Invasive plant species (NNIs)? The more specific questions are: is the removal of Non-Native Invasive plant species an effective method, which slows or prevents re-growth; and, does the removal of Non-Native Invasive plants promote the restoration and re-growth/re-colonization of native plant species? I hope that the removal of Non-Native Invasive plant species will be effective over time and that this will promote the growth of native plants.
I began my research by completing the Montgomery County “Weed Warriors” training course which teaches identification and removal techniques for Non-Native Invasive plants. A certified “Weed Warrior” is permitted to remove invasive species from County Parks and in Regional Parks of Montgomery County, Maryland.
Every week, I selected an area where I removed all of the Non-Native Invasive plant species in a section of Matthew Henson State Park.
What are “Non Native Invasive” Plants?
I found that Non Native Invasive Plants (NNI) are species of plants that were introduced, most of them intentionally, from areas that are beyond their natural range of dispersal. NNIs are often very adaptable, aggressive, and have a high reproductive capacity. When invasive plant species colonize a new area, they often gain an ecological “edge” over the native plants because the insects, diseases, and foraging animals, that naturally keep these plants’ growth in check, in its native ecosystem, are not present in its new habitat.
Why are “Non Native Invasive” Plants a problem?
Non Native Invasive plants are harmful to the local ecosystem. These plants did not evolve in the local environment, but were brought here from thousands of miles away. Non Native Invasive plants often “crowd out” native species - by germinating earlier, covering over other plants, and by being profuse seeders – thereby taking over an entire ecosystem. The loss of native vegetation affects the native insect and bird species, who no longer have the plants to eat or use as nests. Some native animals, such as deer, will not eat invasive plants while other native animals, such as birds, prefer the sweeter berries from invasive plants to native berries –which contain less sugar but has the lipids that birds need to survive the winter . Non Native Invasive plants cause a great loss of biodiversity.
What “Non Native Invasive” Plants are found in Matthew Henson State Park?
The most common Non Native Invasive plants in Matthew Henson include, but are not limited to: Japanese Stilt Grass, Mile-a-Minute Vine, and Wine Berry Vines. Less common Non Native Invasive plant include Porcelain Berry, Canadian Thistle, and Garlic Mustard.
Japanese Stilt Grass [Microstegium vimineum]
Japanese Stilt Grass is probably the most pervasive invasive plant in the Turkey Branch ecosystem.
According to the University of Maine:
“Japanese stilt grass is a highly aggressive species capable of colonizing a wide variety of habitats. It is successful in both high and low light conditions and in moist to moderately dry soils. It readily invades natural areas, replacing native species with nearly monospecific stands. It spreads opportunistically following disturbance, especially where canopy openings have resulted…”
Mile-a-Minute Vine [Polygonum perfoliatum]
The second most pervasive invasive plants in the Turkey Branch ecosystem is the Mile-a-Minute Vine, also known as Devil’s Tear and Tearthumb. According to the University of Maine:
“Mile-a-minute weed grows rapidly, reputedly up to six inches per day, sprawling over other vegetation and blocking sunlight. Thickets of mile-a-minute weed can reduce plant diversity in natural areas and degrade wildlife habitat. It is particularly aggressive in riparian areas (land adjacent to rivers and streams), a habitat type that many animal species depend upon. Mile-a-minute weed is a threat to tree regeneration in open areas such as plantations and nurseries. The species spreads via birds and waterways. Birds eat the abundant fleshy berries and spread the seeds in their droppings. Birds are probably responsible for the spread of this species along power lines and fencerows, and in old fields. The berries float, which probably helps spread the plant along stream corridors. These efficient methods of spread have helped this invader become widely distributed in a relatively short period of time.”
Wine Berry Vines [Rubus phoenicolasius]
According to the Wisconsin Department of Natural Resources:
“The Wineberry is a perennial shrub with long arching canes (stems) up to 9 feet in length. Wineberry comes from Asia and has become a serious pest in eastern and Midwestern states. It produces a large number of fruits that are readily eaten and dispersed by birds. Seeds passed by birds sprout and form dense, impenetrable thickets, crowding out native vegetation. It also spreads vegetatively when tips of the canes touch the soil, take root and produce new plants. Wineberry prefers moist soils and plenty of sunlight but can thrive in disturbed areas, wetlands, forest edges, floodplains, open-canopy woodlands and roadsides.”
Results
Introduction
Every week, I selected an area where I removed all invasive plant species in a section of Matthew Henson State Park. After 12 weeks of clearing weeds, I decided to use statistical analysis in order to determine the effectives of my weeding efforts. I chose 12 weeks because some plants are beginning to go to seed. I wanted to see if my efforts reduced the number of invasive plants and if these efforts enabled more native plant species to flourish.
My methodology is to select a number of areas, measuring 3 feet by 3 feet, in places that I weeded between 1 to 12 weeks ago. I uprooted and counted every invasive plant and also counted the native plants that were left in the ground. I also selected 20 3 feet by 3 feet areas in places that I did not weed to use as a “control” group [see tables 5 and 6]. I then compared the average number of invasive plants/square yard with my control [non-weeded areas'] average. I also compared the average number of native plants/square yard in weeded areas to the average for the “control” areas.
In order to determine if the average number of invasive plants/square yard were significantly different between areas that I weeded and the control areas, that I did not weed, and whether the average number of native plants/square yard were significantly different between areas that I weeded and the control areas, that I did not weed, I used the Student t Test.
where :
X1 = the average number of invasive plants/square yard in areas I have not weeded
X2 = the average number of invasive plants/square yard in areas I weeded
s1 is that variance of untreated areas and s2 the variance of the weeded areas and n1 and n2 are the number of samples.
My Null Hypothesis is:
There is no statistically significant difference in the average number of invasive plants/square yard between areas where I weeded and areas that I did not weed.
There is also no statistically significant difference between the average number of native plants/square yard in the areas that I weeded and those areas that I did not weed.
My Research Hypothesis is:
There is a statistically significant difference in the average number of invasive plants/square yard between areas where I weeded and areas that I did not weed.
There is also a statistically significant difference between the average number of native plants/square yard in the areas that I weeded and those areas that I did not weed.
At the 99% confidence interval, with 38 degrees of freedom ((n1+n2) – 2) the table value is 2.7. If my t value is greater than 2.7, I accept the Research Hypothesis over the Null Hypothesis.
Assessing the Success in the Removal of Invasive Plant Species
I did not have much success in restoring native plants. When I compared the average number of native species/square yard in weeded areas to the average number of native species/square yard in the “control” area, I find the following student t test values:
Weeks Since Last Weeded t test value
1-3 Weeks 3.5
4-6 Weeks 3.3
7-8 Weeks 3.3
9-12 Weeks 3.3
Weeding invasive plants is effective in spite of the fact that some invasive plants grow back over time. Areas weeded three months ago have significantly fewer invasive plants than when compared to un-weeded areas which had an average of 181 invasive plants/square yard. These findings can be seen graphically:
Assessing the Success in the Restoration of Native Plant Species
Weeding out NNIs did not have contribute in restoring native plants. When I compared the average number of native species/square yard in weeded areas to the average number of native species/square yard in the “control” area, I found the following student t test values:
Weeks Since Last Weeded t test value
1-3 Weeks 0.8
4-6 Weeks 2.1
7-8 Weeks 1.0
9-12 Weeks 0.7
This finding is not surprising. Most of the native plants are eaten by deer. Deer do not eat, or forage, in areas where Japanese Stilt Grass (the number one invasive in Matthew Henson Park) is growing. So, once this invasive is removed, the deer eat the natives.
Conclusion
This study has found that it is not been possible to entirely eliminate invasive plant species from an area. However, this study has found, and shown statistically, that weeding significantly reduced the number of invasive plants in the ecosystem. It appears, from the graph, that re-weeding after the forth week may be an effective means of limiting re-growth of invasive plant species.
This study found that weeded areas did not host larger native plant populations compared to un-weeded (control) areas. Sadly, by removing invasive plants, such as Japanese Stilt Grass - through which deer will not forage for food - native plants were exposed and eaten.
I will continue in my efforts to restore Matthew Henson’s ecosystem and will use what I have learned this year to increase the effectiveness of my efforts. I will also monitor the effectiveness of the removal of invasive plant species over more than one growing season.
Citations
“Current and Historical Rare, Threatened, and Endangered Species of Montgomery County, Maryland*”. Maryland Department of Natural Resources Wildlife and Heritage Service, 2007. Web. Sep. 24, 2010
“Invasive Species: About NISIC – What is an Invasive Species?”. National Invasive Species Information Center. Jan 2010. Web. Sep. 24, 2010.
“Invasive Species.” Federal Register 64 (25). Executive Order 13112 of February 3, 1999: 6183-6186.
“Invasive Species – Wineberry or Wine Raspberry (Rubus phoenicolasius) – WDNR.” Wisconsin Department of Natural Resources. N.p., n.d. Web. Sep. 24, 2010.
“Rock Creek Watershed Restoration Action Plan, July 2001.” Montgomery County Department of Environmental Protection, Rockville, MD, Jul. 2010. Web. Sep. 24, 2010.
“The T-Test.” Social Research Methods. Oct. 20, 2066. Web. Sep. 24, 2010.
“Turkey Branch Watershed Restoration”. Montgomery County Department of Environmental Protection, Rockville, MD, Dec. 2006. Web. Sep. 24, 2010.
“The University of Maine – Cooperative Extension Publication – Bulletin #2533”. The University of Maine. 2004. Web. Sep. 24, 2010.
“The University of Maine – Cooperative Extension Publication – Bulletin #2529”. The University of Maine. 2004. Web. Sep. 24, 2010.
“Watershed Restoration Fact Sheets.” Montgomery County Department of Environmental Protection, Rockville, MD. < Watershed Restoration Factsheets. >
Appendix
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