By: Christopher Aultman, Dylan Henry, Charlotte Leivo
The following paragraphs will go into detail about the early records, uses and likely reason that contributed to the popularity and naturalization of the following groundcover species: English Ivy (Hedera helix), Lily of the Valley (Convallaria majalis), Goutweed (Aegopodium podagraria) and Periwinkle (Vinca minor).
English Ivy, Hedera helix, has been widely used by early Europeans as an insulator on stone buildings throughout the year (Sternberg, Viles, Cathersides, & Edwards, 2010). This may have had a large impact on English Ivy being imported to North America, with early records placing the plant in Virginia by 1762 (Wells & Brown 2000). The plant later became widely used for aesthetic purposes instead of as an insulator with the change of heating systems and house design (Sternberg, Viles, Cathersides, & Edwards 2010). The horticulture industry utilized the appeal of this plant to sell and distribute the ivy across North America, with the American Ivy Society widely promoting it currently (Waggy, 2010). Despite the horticulture industry’s success with selling English Ivy, it is having a profoundly negative impact on the natural ecosystem. The ivy was used for erosion control in the 1900’s which may have contributed to the plant’s establishment in many areas across United States. Birds also contribute to the dispersal of the seeds (Waggy, 2010). These factors have likely contributed to the plant negatively impacting the forestry industry by disrupting the growth patterns of the forest, which indirectly impacts the local distribution of the animal species (Waggy, 2010).
Lily of the Valley, Convallaria majalis, has been widely depicted in ancient lore with associations to the Virgin Mary being called Our Lady’s Tears and the virgin goddess of Ostara in Germany when they were pagans. (World of flowering plants, 2014) The plant was further used in a wine concoction to treat various ailments leading to the liquid being known as “Golden Water”. (Haas, N.D) These deeply rooted legends and uses in the culture of early Europeans may have lead to the plant being widely cultivated in North America. The American Gardening book indicates that Lily of the Valley was exclusively imported from Germany in the 1800’s. (Bailey, 1894) As time progress the plant was recommended to be planted for numerous hardy conditions where no other exotic plants would survive. (Bailey, 1894) This plant then escaped cultivation, becoming naturalized in native ecosystem and having the same effect on the landscape as the other groundcovers.
Goutweed, Aegopodium podagraria, was brought over by colonial settlers to America with early records placing it in North America since the 1850’s. (Waggy, 2010) Historically, goutweed was used for food and for its medicinal properties in treating gout, in many European countries, this was likely the reason behind bring the plant to North America. (Waggy, 2010) Goutweed is now being grown as an ornamental groundcover because of its rapid growth rate and hardiness in many environments. Nurseries throughout North America have widely promoted the plant for this use. (Waggy, 2010) As people became more irritated with the plant outcompeting the other plants in the garden people have disposed of the plant in various forests to be rid of the plant. (Waggy, 2010) This is now creating problems for the overall health of ecosystems and is getting the attention of the forestry industry and other natural groups.
Like goutweed, periwinkle was likely brought over initially for its edibility by early European settlers. Early records indicate that periwinkle has been in Virginia since 1771(Wells & Brown, 2000) but may have been in North America earlier than this. The range of periwinkle is due to the horticulture industry, in the American Gardening book periwinkle was recommended on numerous accounts to be used for erosion control along the riparian zone (Bailey, 1894). This could have impacted the naturalization of the plant in native ecosystems in North America. As time progressed the plant was widely distributed and sold in many greenhouses and nurseries in North America for its gorgeous blue flowers and tolerance for shade (Stone, 2009). It is likely that periwinkle escaped cultivation from homes that bordered forested ecosystems (Darcy & Burkart, 2002), bringing rise to problems in the environment.
The reproductive strategies deployed by the following groundcovers; Goutweed, Lily of the Valley, English Ivy, and Periwinkle have contributed to the successful establishment of the natural environment. Once in an ecosystem the rapid expansion by vegetative growth allowed the groundcovers to quickly form dense mats on the forest floor. This resulted in outcompeting native plant species and restricting available sunlight that killed germinating native flora, including tree species (Waggy, 2010. Stone, 2009. Darcy & Burkart, 2002). The ability of English Ivy to grow vertically on trees and the use of adventitious roots allows it to create what is known as “Ivy deserts” in a forest as it affects all strata of a forest (Waggy, 2010). The rhizomes of goutweed and lily of the valley allow them to grow in numerous soil and shade conditions. Where then creep inward to areas that their seeds cannot properly germinate. The strong fragrances of these two groundcovers have been known to attract numerous pollinators to their flowers (Waggy, 2010. Ohara, Araki, Yamada, Kawano, 2006).
Other factors that possibly lead to these plants becoming established in an Ecosystem would be disturbed ecosystems. These ecosystems could have become disturbed by different factors. Overabundance of deer within an ecosystem results in the deer over browsing the native flora, which would lead to an open space where these invasive plant species can enter the area (Rawinski, 2008). Once these plants establish they quickly grow out of control unopposed because the deer do not favour these exotic plants. Other factors could be recent fires that disrupted the ecosystem or improper human management of the forest stands.
The negative impacts that the groundcovers have on a forest has recently started to raise concerns with environmental-related organizations and naturalist alike as they are decreasing the biodiversity in these forest ecosystems. As the formation of dense mats on the forest floor are affecting the forest’s ability to replenish varying levels in the canopy layer, weakening the overall health of the forest (Waggy, 2010). The biggest concerns for this comes from Periwinkle and English Ivy based on studies that confirmed they had an incredibly negative effect on the germination and growth of seedlings (Waggy, 2010. Darcy and Burkart, 2002). The high fragrance of goutweed and lily of the valley has gotten naturalists concerned about the pollinator to native plant species interaction, which may lower the seed reproduction of wanted native plant species (Waggy, 2010. Ohara, Araki, Yamada, & Kawano, 2006). Periwinkle, English Ivy and Goutweed have been known to negatively impact riparian zones and floodplains as they widely establish themselves in these areas or were once used as erosion control in these locations (Waggy, 2010). Furthermore, as native plants species begin to disappear in regions native fauna will begin to decrease in areas where these ground covers are taking over the forests.
Critical Assessment of Current Management Strategies:
Introduced invasive plants threaten ecosystems due to their excessive growth and have both ecological and economic impacts. Invasive species threaten native wildlife and ecosystems and are causing ecological havoc in many of our most sensitive habitats, pushing many of our native plants and animals to the brink of extinction (Padullés & Vila & Barriocanal, 2015). Each method option is described in the next paragraphs.
The best way to ultimately control these groundcover species is prevention. This can be achieved by maintaining a healthy ecosystem where these plants cannot establish themselves in. Other methods of preventing these species from invading these natural spaces is to educate the public on ways to ensure the plant cannot spread into these ecosystems. Like not planting these plants on areas that border the ecosystem where they could spread vegetatively or creating deep barriers that the roots would not be able to grow past.However, if the plants have already established themselves in these regions there are the following methods of control: Do nothing, Biological Control, Chemical Control, Mechanical or Physical Control. The following paragraphs will go into detail for the effectiveness of each control for English Ivy, Goutweed, Lily of the Valley, and Periwinkle.
Doing nothing is always an approach that can be taken to address this issue. Many people have voiced their opinion on the severity of invasive species establishing themselves in an environment or if it’s just natural and these species are just becoming integrated in the environment. This suggests that if a long enough time passes these plant species will be adopted into the diet of native fauna as some evidence of White-tailed Deer and Volcano Rabbit browsing on Periwinkle (Stone, 2009) is already coming to light. English Ivy is another plant species that has been documented to be incorporated in White-tailed Deer diets (Waggy, 2010). Currently there is no known species that native species that consume lily of the valley or goutweed but it has been noted that many pollinator species are widely attracted to these species and aid in the pollination. However, if these plants are left alone to grow out of control it would completely disrupt many ecological functions in an environment as they spread quickly by rhizomes and will out-compete all layers of a forest by restricting light to tree seedlings or ground flora (Stone, 2003. Waggy, 2010). Several studies focusing on the effects of leaving certain study plots unchecked in Michigan, Illinois, Oregon, Sweden, Czech Republic and the Netherlands indicate that the plant populations exponentially in the environment if unopposed. Resulting in potential losses in the Forestry Industry as wood production in these areas begin to decline without the growth of new trees. Other similar industries that benefit from resources coming from these forest ecosystems may also be negatively impacted.
Biological control is another control method that proves to be effective in multiple studies that took place in Europe and United States for Goutweed, English Ivy and Periwinkle. One common biological control method for these species are the use of livestock; cattle, goats and sheep to limit or eliminate these species from an environment. In Oregon, a study was performed to look at the effects of goat browsing on English Ivy in managed plots in a forest ecosystem. The study showed that high intensity, short duration browsing of the juvenile stages of English Ivy resulted in the decrease of plant cover to 23% in the 1st year of browsing, and to 4% plant cover in the following year (Ingham & Borman, 2010). A similar study has been performed in New Zealand but substituted with sheep instead of the goat that yielded similar results. Another study done in the Netherlands showed the effects of large cattle browsing in forest ecosystems of bramble and groundcovers. This study showed that the effects of cattle browse and trampling effects on the ecosystem resulted in English Ivy and Periwinkle to disappear in the plot by 2004 despite there being no significant difference in frequency between the ungrazed and grazed plot in 2002 (Van Uytvanck & Hoffman, 2009). A study that was conducted in the Czech Republic, examined the effects of cattle grazing on forb species at a grassland site, the site contained varying intensities of Goutweed. This study revealed that varying intensities of cattle grazing resulted in the vast decrease or disappearance of Goutweed present at the pasture plots (Pavlů, Hejcman, Pavlů, Gaisler, & Nežerková, 2006). Therefore indicating that livestock browsing of all three species can be executed in a forest ecosystem and be effective in managing these invasive groundcovers species, the exception being Lily of the Valley. The study based out of Oregon further indicated that goats could be used within urban parks. (Ingham & Borman, 2010) The management strategy utilizes the agricultural industry to control invasive species in an ecosystem indicating the combined benefits of providing food for livestock that may be used for producing dairy, food, and/or textile products. Making this method cost effective as there is a source of income coming in from the used animal species but could cause other problems as the may consume wanted native flora and could compact the soils depending on the animals used.
Chemical control methods may be one of the most commonly used management strategies for large populations of invasive plant species throughout Canada and the United States of America. A study was done in Oregon that indicated performing chemical control on English Ivy in the winter proved to be effective (Waggy, 2010). Further studies completed in New Zealand indicated that basal application after the mature plant was cut proved effective for a short duration (Griffiths, 2010). It has been noted that Goutweed and Periwinkle persist after the use of Glyphosates because of the vegetative growth response following the procedures and the deep rhizomes that likely were not affected by the spraying (Waggy, 2010. Stone, 2009). The same is true for Lily of the Valley because it contains deeply rooted rhizomes that escapes the chemicals (Kosinski, 2003). Therefore proving that the application of herbicides is only a short-term solution to a long-term problem.
physical and mechanical control:
The most common way that many conservation areas remove invasive ground cover like periwinkle and goutweed is by implementing physical and mechanical control methods to remove the plant body and roots (CVC, 2017). This method of removal is only effective if the entire root mass is removed due to rhizomes being able to rapidly recolonize in the soil. If the entire plant is not removed the plant will continues to grow new shoots (CVC, 2017). Excavation can be very affordable if completed with volunteers and hand tools. However heavy machinery can be used which will increase cost but reduce the duration of the project. In some cases these methods are the only available control methods for invasive plant species that do not utilize chemicals, Lily of the Valley is one of these species. A study done in Poland, simulated the effects an animal would have if they were to consume Lily of the Valley on a yearly basis by continually mowing populations of the plant (Kosinski, 2003). This study was successful in showing that if Lily of the Valley was intensively mowed back and trampled upon, the plant will decrease in vegetative cover (Kosinski, 2003). However, some of these methods may not be effective in a forest ecosystem as it will provide an entry point for new invasive species or will make it so new species cannot regrow in the area this is dependant on the material used to smother the plant. Therefore, indicating that these methods are best used in conjunction of previously mention methods to effectively remove the species or strategies of replanting native plant species in the area immediately following these methods. This method is incredibly physically demanding and involves a lot of labour if done on a larger scale, thus being an ineffective of management due to the high resource need.
Table 1: Illustrates a comparison of doing nothing,biological control, fire management, physical and mechanical control, herbicides and prevention as a method to resolve the invasion of Vinca minor L., Convallaria majalis, Aegopodium podagraria & Hedera helix in North America.
|Do Nothing||$||Cost Effective||Would cost more to maintain landscape with the outspread of targeted species expanding. Species would continue to thrive and choke out native plants.||–|
|Biological Control||$$||Effective in natural removal and fertilizing of area.||Consumes wanted native plant species.||+|
|Physical and Mechanical Control||$$-$$$$||Only targeted species are removed from the area. Can be cheap.||Labour intensive. Soil compaction. Disturbed soils could provide suitable germination for other invasives||+|
|Herbicides||$$$||Effective initial short-term treatment||Plants that are not targeted may also be affected by spray methods||–|
|Prevention||$||Natural ecosystem restored.||Effective in preventing plants initially but does not work if the invasive plants are already present.||++|
Bailey, L.H. (1894) American Gardening: A Journal of Horticulture. 1893-1894 (Vol. 15). New York, NY: A. T. De La Mare PTG. & PUB. CO., Ltd.
Darcy, A.J., & Burkart, M.C. (2002). Allelopathic Potential of Vinca minor, an Invasive Exotic Plant in West Michigan Forests. Bios, 73(4), 127-132. Retrieved from http://www.jstor.org/stable/4608646
Griffiths, K. (2010) Control methods of English Ivy in Puahanui Bush, NZ. The Conservation Company LTD. Retrieved from http://www.theconservationcompany.co.nz/pdf/Control%20methods%20for%20English%20ivy.pdf
Haas, L.F. (N.D). Convallari majalis (lily of the valley) (also known as Our Lady’s tears, ladder to heaven).Journal of Neurology, Neurosurgery & Psychiatry 1995;59:367.
Ingham, C. S., & Borman, M. M. (2010). English Ivy (Hedera spp., Araliaceae) Response to Goat Browsing. Invasive Plant Science & Management, 3(2), 178-181. doi:10.1614/IPSM-09-021.1\
Kosinski, I. (2003) The Influence of Shoot Harvesting on the Age Structure of Convallaria majalis L. Populations. Acta Societatis Botanicorum Poloniae (Vol 72). No. 1: 53-59,2003
Ohara, M., Araki, K., Yamada, E., & Kawano, S. (2006). Life-history monographs of Japanese plants. 6: Convallaria keiskei Miq. (Convallariaceae). Plant Species Biology, 21(2), 119-126. doi:10.1111/j.1442-1984.2006.00157.x
Pavlů, V., Hejcman, M., Pavlů, L., Gaisler, J., & Nežerková, P. (2006). Effect of continuous grazing on forage quality, quantity and animal performance. Agriculture, Ecosystems And Environment, 113349-355. doi:10.1016/j.agee.2005.10.010
Padullés Cubino, J., Vila Subirós, J., & Barriocanal Lozano, C. (2015). Propagule pressure from invasive plant species in gardens in low-density suburban areas of the Costa Brava (Spain). Urban Forestry & Urban Greening, 14941-951. doi:10.1016/j.ufug.2015.09.002
Rawinski, T.J. (2008) Impacts of White-Tailed Deer Overabundance in Forest Ecosystems Overview. Forest Service, U.S. Department of Agriculture, Northeastern Area State and Private Forestry. (Producer). Retrieved from https://www.na.fs.fed.us/fhp/special_interests/white_tailed_deer.pdf
Sternberg, T., Viles, H., Cathersides, A., & Edwards, M. (2010). Dust particulate absorption by ivy (Hedera helix L) on historic walls in urban environments. Science Of The Total Environment, 409162-168. doi:10.1016/j.scitotenv.2010.09.022
Stone, K.R (2009) Vinca Major, V, Minor. In: Fire Effects Information System [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Retrieved from http://www.fs.fed.us/database/feis/plants/vines/vinspp/all.html
Vandepitte, K., De Meyer, T., Jacquemyn, H., Roldan-Ruiz, I., & Honnay, O. (2013). The Impact of extensive clonal growth on fine-scale matting patterns: a full paternity analysis of a lily-of-the-valley population (Convallaria majalis). Annals of Botany, 111(4), 623-628
Van Uytvanck, J., & Hoffman, M. (2009) Impact of grazing management with large herbivores on forest ground flora and bramble understory. Acta Oecologia, 35(4):523-532. DOI: 10.106/j.actao.2009.04.001
Waggy, M. A. (2010) Aegopodium podagraria. In: Fire Effects Information System. [Online.] U.S Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Retrieved from https://www.fs.fed.us/database/feis/plants/forb/aegpod/all.html
Waggy, M. A. (2010) Hedera helix. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2017, February 11].
Wells, E., & Brown R.L. (2000). An Annotated Checklist of the Vascular Plants in the Forest at Historic Mount Vernon, Virginia: A Legacy from the Past. Castanea, 65(4), 242-257. Retrieved from http://www.jstor.org/stable/4034007
World of Flowering Plants (2014) Legends and Facts about the Lily of the Valley. (Online) Retrieved from http://worldoffloweringplants.com/legends-facts-lily-valley/