September 5, 2019
Plant Talk 10 Exotic Invasives
Hello plant enthusiasts,
i also taught classes on Challenges and Opportunities with Exotic Invasive Plants at Living Web Farms and Medicinal Polypores for the Asheville Mushroom Club. The Living Web class will eventually be up on the You Tube channel in video form…
Some upcoming events where I will be working in the next few weeks follow including the Chow Chow Food festival, Mountain State Fair, Roan Mountain Naturalist Rally, and United Plant Savers anniversary.
Anise Hyssop (Agastache foeniculum) from the Lamiaceae
Clematis spp. Ranunculaceae
Four O’Clocks (Mirabilis spp.) Nyctaginaceae
Gentian (Gentiana spp.) Gentianiaceae
Nasturtiums (Tropaeolum majus) Tropaeolaceae
Trees and shrubs include Abelia x grandiflora
But the lion’s share of the blooms this time of year belong to the Asteraceae including, Beggar’s Ticks (Bidens spp.) Boneset (Eupatorium perfoliatum), Compass Plant (Silphium spp.), Coreopsis spp., Echinacea spp., Goldenrods (Euthamia spp., Solidago spp.), Ironweeds (Vernonia spp.), Marigolds (Tagetes spp.), Ragweed (Ambrosia spp.), Sunflower (Helianthus spp.), Wingstems (Verbesina spp.) and Zinnia spp. to name a few.
Fruits Ready for Harvest
Apples (Malus spp.), Asian Dogwood (Cornus kousa), Autumn Olive (Elaeagnus umbellata), Pawpaw (Asimina triloba), Pears (Pyrus spp.), Persimmons (Diospyros virginina), Plums (Prunus sp.), and Spice Bush (Lindera benzoin) fruits are ready and rocking just to name a few! The Blueberries (Vaccinium spp.) at upper elevations such as Sam’s Knob are peaked, but Black Fruited Viburnums (Viburnum spp.) and American Rowan (Sorbus americana) will be ready to pick up their soon.
Tomatoes are barely hanging on but Peppers from the same Solanaceae family are bumping. Will be making the first round of hotsauce soon. i have a little Pepperetum including the hottest pepper in the world “Carolina Reaper” and other legendary varieties like “Ancho”, “Cayenne”, “Ghost Bhut”, “Habanero”, “Jalapeño” “Serrano” and “Thai Hot”.
Introduction to Exotic and Invasive Plants and the Evolution of my Personal Connection to Them
Exotic invasives are a topic that i have explored for a many years starting with my graduate research in 2007. The following is a revision and distillation from my graduate research which initially focused on information for the southeastern U.S. but now features information from around the country as well as other countries such as Australia, Canada, Hungary, Israel and New Zealand.
Many names are given for exotic invasives. These include noxious, nonindigenous, alien, and non-native weeds. Andow (2005) offers a general definition. “Invasive alien species become established in natural or semi-natural ecosystem or habitat, are agents of change and threaten native biological diversity.” Invasive plants may come from far away continents or adjoining areas within one continent. In the U.S. most exotic invasive plants come from Europe or Asia collectively known as Eurasia.
The study of this issue is a central focus within the science of Ecology (Bazely, 2003; Booth, Murphy, & Swanton, 2011; Elton, 2000; Graham, 2010; Monaco & Sheley, 2012; Myers, 2003; Ross & Lembi, 2009; Shibu, 2013; Vilà et al., 2011).
The author Charles Mann fairly recently wrote a book called 1493 (2011), which is a sequel to 1491 (2006) and in it he explores in part how vastly transformed the landscape of America has become due to the presence of recently introduced organisms. This phenomenon includes not only plants, but microbes, insects, mollusks, rodents, earthworms, and of course people, etc… An interesting piece about the establishment of foreign plants since the 1600s maps the trajectory of the phenomenon into the 1800s as well (R. N. Mack, 2003).
Invasion ecology is the study of how invasive species interact in the environment. It is concerned with five questions: Which taxa invade? How fast? What makes ecosystems invasible? What is the impact? How can we contain, control, or eradicate harmful invaders? All of these questions are related to the particular habitat in question (Radosevich, Holt, & Ghersa, 2007; Rejmanek, 2005).
Many factors relate to whether a plant will become invasive. These include the type of plant and the type of ecosystem in question. Plant characteristics include reproductive strategies, relation to biotic and abiotic forces, age to reproduction, and reproductive success. Specific reproductive strategies include seed dormancy regimes and adaptations for spread by humans and other agents of nature. Plants that have seeds that are the same size and shape of crop seeds may elude winnowing processes (Westbrooks, 1998). Plants that have flexible reproductive regimes are more likely to become invasive. Plants that have a number of pollinators, the potential for self- pollination, and other means of asexual reproduction are some examples. Plants that reproduce early in their life cycle and make copious amounts of seeds that are readily distributed are also potential invasives.
Other plant characteristics that aid in invasiveness include; long life, production of biological toxins, prickles, spines, thorns, the ability to parasitize other plants, and a high photosynthetic rate. Plants that show “fitness homeostasis” or the ability to flourish in a number of environments have a larger potential to become exotic invasives (Rejmanek, 2005). St John’s Wort (Hypericum perforatum) is a big problem in the western USA due to its ability to cause photosensitivity in livestock. Thistles of various types such as Star Thistle out west (Centaurea solstitialis) and various species from other Aster family genera all over are well known for their spines i.e. (Cirsium spp., Carduus spp., Carthamus spp. and Milk Thistle Silybum marianum).
Ecosystem characteristics that effect exotic invasive potential include, availability of water, climate regime, position as a disturbed or climax environment, soil quality, nutrient resource availability, species diversity, and the type of plants already present. Characteristics of reproduction, historical exposure to selective pressure, and post-disturbance recovery rates are factors related to the resistance of plants that are already present to the invasion by exotics.
Only a fraction of introduced species are actually detrimental. These are known as “transformer species”. These plants actually change the character of the ecosystem that they inhabit. There are several ways in which a species may change the ecosystem including excessive use of water, changing the nutrient regime, changing the fire regime, altering the pattern of erosion, accumulation of litter, altering carbon storage, and accumulation of salt (Cronk & Fuller, 2001; Rejmanek, 2005). Some studies have looked directly on the effect to fire regimes and soil regarding exotic invasives (M. Brooks, 2013; M. L. Brooks et al., 2004; Ehrenfeld, 2003).
Trends in Exotic Invasive Plant Potential
Some families seem to exhibit more of a propensity toward invasiveness. These include the
Likewise, some families are underrepresented in the exotic invasive flora including Acanthaceae, Orchidaceae, Podocarpaceae, Rubiaceae, and Zamiaceae. However, even in these underrepresented families exceptions do exist (Mooney, 2005).
According to the data from www.invasives.org NC, SC, TN, GA, KY, and VA have 300 species listed at some level of invasiveness (Miller, Chambliss, & Bargeron, 2006). These plants represent 76 Families. Forty families have only one species represented, while eight families have only two species represented. Sixteen families have between three and five species represented. The remaining eleven families have 178 species represented. This includes well over half the total. The eleven top invasive families follow including the number of representative species in parentheses;
Grass family, Poaceae (61)
Figwort family, Scrophulariaceae (8)
Aster family, Asteraceae (28)
Rose family, Rosaceae (8)
Bean family, Fabaceae (27)
Honeysuckle family, Caprifoliaceae (8)
Mint family, Lamiaceae (10)
Tomato family, Solanaceae (6)
Smartweed family, Polygonaceae (9)
Mustard family, Brassicaceae (6)
Bindweed family, Convolvulaceae (9).
The top three families listed have over one third of the total number of invasive species! Asteraceae, Fabaceae and Poaceae are three of the most diverse species rich families in the world. However, they still represent a disproportionate amount of invasives given their percentage of total world flowering plant flora. Asteraceae contains roughly 25,000 spp. Fabaceae has about 19,350 spp. and Poaceae has about 10,000 spp. out of a total of approx 350,000 spp. (Groombridge & Jenkins, 2002; Heywood, Brummitt, Culham, & Seberg, 2007; “Home,” 2016). This equals roughly 17% of total world flora. The data related to plant family level invasiveness may be used in conjunction with other information to predict possible invasive tendencies. Correlating acreage affected by family and even genus may help set priorities of which invasive plants to control first. Genus diversity within prevalent exotic invasive plant families might also give clues as to the propensity of certain plants to invade.
The predominant life forms of invading plants in the southeastern USA are listed here with number of species following in parentheses; Forbs/Herbs (118), Grasses (61), Shrubs (39), Vines (30), Aquatic Plants (26) and Trees (19) (Miller et al., 2006). Connecting acreage affected with plant form may also help set control priorities. Unfortunately, at this time much work is left to be done in analyzing how many acres are truly affected by this diverse array of species. Some estimates have been made for individual species. For instance, Kudzu (Pueraria montana) and Japanese honeysuckle (Lonicera japonica) alone are often thought to cover millions of acres (Forseth & Innis, 2004; Lemke, Hulme, Brown, & Tadesse, 2011). Total coverage by exotic invasives in the U.S. in 1998 already amounted to well over 100 million acres and was estimated to be growing at a rate of 8-20% annually (U.S. Dept of Interior, 1998). The use of Geographic Information Systems (GIS) and satellite imagery may help characterize the nature of coverage by various exotic invasive plants (Shawna J. Dark, 2004; Gelbard & Belnap, 2003; Pyšek et al., 2004).
Some exotic invasives have been studied rather in depth like Japanese Knotweed (Reynoutria japonica) (Child, 1999; Child & Wade, 2000; Gerber et al., 2008; Hulina & Đumija, 1999; Kelley, 2016; Lecerf, 2007; D. Moore, 2006).
Another one would be Garlic Mustard (Alliaria petiolata) (D. J. Burke, 2008; Cipollini & Gruner, 2007; Kathryn Barto & Cipollini, 2009; Lankau, 2011; McCarthy & Hanson, 1998; Prati & Bossdorf, 2004; Rodgers, Stinson, & Finzi, 2008; Vaughn & Berhow, 1999; Wixted & McGraw, 2010).
Many others are in need of further study. One study clearly shows that plants like Privet (Ligustrum sp.) at 3.2 million acres and Multiflora Rose (Rosa multiflora) at almost a million acres are much bigger problems in regards to total acreage covered compared to the current assessment of Kudzu at 227,000 acres (Finch, 2015).
Scope of Exotic Invasive Plants
Invasive species tend to continue to proliferate, unlike other forms of pollution that may naturally degrade over time once the source has been controlled (Weber, 2003). Exotic invasives can lower the value of land for various uses. The control of exotics and losses of production because of them cost billions of dollars each year plus other costs to the environment as well (Burrell, 2006; Keller, Lodge, Lewis, & Shogren, 2009; Myers, 2003; Pimentel, Zuniga, & Morrison, 2005; Vilà et al., 2011).
About 8,000 species or just over 2% of all known plants are considered to be invasive. Of these about 200-250 spp. or approx .07% of the total known species are recognized as major problems in world agriculture, with about 80 taxa representing the primary and most troublesome species (Westbrooks, 1998). At least 4,500 species of foreign plants and animals have been introduced that have free-living populations in the U.S. since the time of European colonization. Of that total at least 675 cause some form of economic damage (Westbrooks, 1998). Almost 3,500 species of plants are recognized as weeds in the U.S. (Weed Science Society of America, 2007). Typically about 65% of weeds come from exotic locales. Some references also cover the scope of worldwide weeds as well (L. Holm, Doll, Holm, Pancho, & Herberger, 1997; L. G. Holm, 1991; Weber, 2017).
A lot of work has been done from researchers in different ecotypes about the nature of plant invasions. In New England some region specific literature has been generated (Gavier-Pizarro Gregorio I., Radeloff Volker C., Stewart Susan I., Huebner Cynthia D., & Keuler Nicholas S., 2010; Huebner, Olson, & Smith, 2005; Royer & Dickinson, 1999). Connecticut has a nice array of specific resources for the state (Bugbee & Balfour, 2010; Capers, 2005; Connecticut Invasive Plant Council, 2004). Nearby Massachusetts has developed a resource as well (Weatherbee & Somers, 1998). Same for Maine (Maine Volunteer Lake Monitoring Program, 2007).
A number of resources are available for the southwestern U.S. too (Chambers & Hall, 2001; Chambers & Hawkins, 2002; Thomas & Guertin, 2007; M. R. White, 2008, 2011).
Likewise for the Pacific Northwest (PNW) (Boersma, Reichard, & Van Buren, 2006; Ciesla, 2002; Gray, Barndt, & Reichard, 2011; Harrington & Reichard, 2007; Sherley, 2000; Skrine, 2005). Alaska at the extreme of the PNW region has a literature all its own (Bauder, 2005; Hébert, 2001; Shephard, 2007). This is also the case a little further inland in Montana (Carpenedo & Saul, 2010; Rens, 2003).
California probably has more published resources than most places (Bossard, Randall, & Hoshovsky, 2000; Coates, 2006; Colvin, 2008; Shawna Jeanette Dark, 2003; Di Tomaso & Johnson, 2006; Donlan, Croll, & Tershy, 2003; K. Moore & Hyland, 2002; Rejmánek & Randall, 1994; Robbins, Bellue, & Ball, 1970; Strauss, Webb, & Salamin, 2006; Williams, Rogers, & Howe, 2013).
The Midwest has a little bit that i have been able to turn up so far (Czarapata, 2005; Gonzalez & Christoffersen, 2006; Gould & Gorchov, 2000; Howe, 2008; Klein, 2004; M. D. Smith & Knapp, 2001; Trebitz & Taylor, 2007). Some state specific references include Oklahoma (Cooper, Oklahoma Invasive Plant Council, & Meeting, 2010; Oklahoma Invasive Plant Council, 2010) Wisconsin (Hoffman & Kearns, 1997; Wisconsin Bureau of Endangered Resources, 2010) and Minnesota (Trails and Waterways Division, 2002).
Many resources for the southeast are cited throughout this class. However to put a fine point on it North Carolina has a couple resources (Cole, Megalos, & Temple, 2013; C. Smith, 2008; Western North Carolina Tomorrow, 2000). Tennessee has at least one specific resource as well (Lambdin & Grant, 2000). Kentucky as well (Haragan, 1991) and Georgia too (C. W. Evans, Bargeron, Moorhead, & Douce, 2008).
Neotropical places like Hawaii have a unique issue for the U.S. in regards to invasives (M. C. Mack, D’Antonio, & Ley, 2001; Staples & Cowie, 2001; Stone, 1993). Palau has one resource I have been able to find as well (DeMeo, 2002). Florida has some similar issues to Polynesia and shares a number of plants with that area as well (Gordon, 1998; Langeland, 1998; Ramey, 2005; Simberloff, Schmitz, & Brown, 1997).
Canada is amongst a number of other countries have developed literature on exotic invasives (Haber, 2000; Havinga, 2000; Lavoie, Jean, Delisle, & Létourneau, 2003; D. J. White, Haber, & Keddy, 1993; Wikeem, 2006).
Australia is another great example of very robust literature in regards to exotic invasives (Ainsworth & Swane, 2004; G. Burke, 1996; Glanznig, Kessal, & McLachlan, 2004; Groves, Lonsdale, & Boden, 2005; Jones, Griffith, & Vere, 2006; Martin, 2003; Navie & Adkins, 2008).
New Zealand also has some (Hetherington, 2012) as does India (Bhatt, 2012).
To get out of the former British colonies i would like to cite work that has been done in Israel, South Africa and Hungary (Botta-Dukát, 2008; Bromilow, 2001; Dufour-Dror, 2012; Henderson, 2001).
Are you aware of a resource about exotic invasives around you? If so please share in the comments below, in an email to me or on the Facebook group.
Effects on Biodiversity
Non-native plants are considered to be the second biggest threat to biodiversity following development (Westbrooks, 1998). Some exotic invasives poison other biota either through allelopathy or through their toxicity to grazing animals. Garlic mustard (Alliaria petiolata) and Tree of Heaven (Ailanthus altissima) are two exotic invasives in Appalachia that exude toxins from their roots that are not good for other plants. Some studies has been conducted on the Tree of Heaven in particular cited here (Buck, 2002; Heisey, 1990, 1996; Lawrence, Colwell, & Sexton, 1991). Numerous studies have been conducted on the effects of Garlic Mustard as well (D. J. Burke, 2008; Cipollini & Gruner, 2007; Kathryn Barto & Cipollini, 2009; Lankau, 2011; McCarthy & Hanson, 1998; Prati & Bossdorf, 2004; Vaughn & Berhow, 1999).
In 1998 the habitat of two-thirds of all threatened and endangered species was already imperiled by invasives (U.S. Dept of Interior, 1998). Exotic invasives can exacerbate the fire regime which may change available habitat for native plants and cause threats to human settlements (M. Brooks, 2013; M. L. Brooks et al., 2004). Chinese Silvergrass (Miscanthus sinensis) is a plant in Appalachia and beyond that may increase fire risk. At the same time this genus is also being looked at as a potential source of biofuel (Christian, Riche, & Yates, 2008; Clifton‐Brown, Breuer, & Jones, 2007; Clifton‐brown, Stampfl, & Jones, 2004; Heaton, Dohleman, & Long, 2008; Khanna, Dhungana, & Clifton-Brown, 2008).
Riparian areas are also often severely affected by exotic invasives (Bugbee & Balfour, 2010; Carpenedo & Saul, 2010; De Waal, 1994; Lavoie et al., 2003; May, 2007; Trebitz & Taylor, 2007; D. J. White et al., 1993; Zedler, 2004). Tamarisk (Tamarix spp.) in the western U.S. is a very challenging problem in riparian areas (Morisette et al., 2006; Wang, Silván-Cárdenas, Yang, & Frazier, 2013).
Native herbivores don’t always feed on non-native plants as readily as food sources they are used to (Darke & Tallamy, 2014; Gosper, Stansbury, & Vivian‐Smith, 2005; S. B. Smith, DeSando, & Pagano, 2013; Tallamy, 2009).(Darke & Tallamy, 2014; Tallamy, 2009).
Open water environments are notorious for the introduction of exotic invasives (Rejmanek et al. 2005). Many plants from just a few families have quickly become noxious weeds.
These families include:
Most of the genera listed for these families have Class A highest priority status in the Carolinas. However, they do not even appear in the standard flora for this area that was written only four decades ago (Radford, Ahles, & Bell, 1968). The absence of such important invasives from a relatively recent survey of plant life shows the quick moving nature of some infestations. Elpel covers many of these exotic invasive water families listed alphabetically. Alismataceae (173), Azollaceae (41), Haloragaceae (112), Najadaceae (174), and Potamogetonaceae (175).
A well-developed literature addresses the phenomenon of aquatic invasions specifically (Bugbee & Balfour, 2010; Capers, 2005; Carpenedo & Saul, 2010; De Waal, 1994; Henderson, 2002; Lecerf, 2007; Maine Volunteer Lake Monitoring Program, 2007; May, 2007; Ramey, 2005; D. J. White et al., 1993; Zedler, 2004). North Carolina State University has also developed and App to identify Aquatic Plants.
How are Exotic Invasive Plants Introduced?
Invasion typically follows a certain order. These steps include introduction, naturalization, facilitation, spread, interaction with animals and other plants, and stabilization (Cronk & Fuller, 2001). Vectors for the introduction of exotic invasive plants include ports, botanical gardens, plant collectors, foreign produce, nurseries, research stations, factories, and travelers.
The rate of spread can vary by orders of magnitude depending on the confluence of various factors (Rejmanek, 2005). Certain vectors are more dangerous than others. This phenomenon is largely due to awareness, scale and repetition of risky behavior. It is necessary to prioritize which vectors are the biggest issues and reduce their potential (Rejmanek, Richardson and Higgins, 2005).
Globalization and the liberalization of trade have led to increased introduction of exotic invasives by accident. Plants have been known to hitchhike on boats or in their ballast water and then set up residence. Domestic sources can also lead to accidental introduction of exotic invasives. For example, hay that is used for mulch may contain seeds of exotics. Hay used for forage on public lands must often be certified weed free (United States, 1998).
Most exotic invasives have been introduced intentionally by the horticulture trade (Weber, 2003; Westbrooks, 1998). “In most countries horticultural releases have been considered safe, and little has been done to manage potential environmental risks of these introductions despite abundant scientific evidence that these introductions can cause environmental harm” (Andow, 2005). According to one study over half the species invading natural areas in the U.S. were introduced through the trade in ornamentals (Randall & Marinelli, 1996). For instance, gardeners at the Biltmore Estate near where i live are thought to be potentially responsible for introducing invasives (Alexander, 2007). Wildflower seed mixtures often contain a certain percentage of weed seeds. Therefore, buyers should acquire mixes with a low percentage of weed seeds and control any weeds that germinate before they become a problem.
Some of the most noxious exotic invasives are still for sale and used for a number of applications. These include Chinese silvergrass (Miscanthus sinensis), Periwinkle (Vinca spp.), Japanese Honeysuckle (Lonicera japonica), Oriental Bittersweet (Celastrus orbiculatus), Lespedeza (Lespedeza spp.), Autumn Olive/Silverthorn (Elaeagnus spp.), and Heavenly Bamboo Nandina domestica. It is hard to understand why the sale of these plants is not outlawed. The continuing sale of known exotic invasives represents an example of externalized costs. The horticulture industry is allowed to make a profit off of something that costs tax payers subsequently many millions of dollars.
Alternatives to planting exotic invasives do exist. Some varieties of Heavenly Bamboo (Nandina domestica) are sterile. Cultivars of Silver Grass (Miscanthus sinensis) can also vary widely in seed viability and fertility (Miller et al., 2006). A number of books speak to the virtues of native plants that have analogous uses to exotic invasives (Ainsworth & Swane, 2004; Burrell, 2006; Dept. of Conservation & Wellington Conservancy, 2005). The North Carolina Native plant society has a list as does the North Carolina botanical garden and NC State University. The NC botanical garden also has a list of sustainable native plants nurseries from across the country.
Using native plants in a garden has many benefits. They attract beneficial wildlife and insects, they allow a gardener to create a garden that reflects the native beauty of the region, and they make a garden more sustainable (Society, 2016). Because of all this, they are an increasingly popular plant choice for home and public gardens. Native Plants of the Southeast shows you how to choose the best native plants and how to use them in the garden (Mellichamp & Stuart, 2014). This complete guide is an invaluable resource, with plant profiles for over 460 species of trees, shrubs, vines, ferns, grasses, and wildflowers. Each plant description includes information about cultivation and propagation, ranges, and hardiness. Comprehensive lists recommend particular plants for difficult situations, as well as plants for attracting butterflies, hummingbirds, and other wildlife. The use of native plants for landscaping will lessen the viable populations that may escape from foreign cultivars. The growth and sale of native plants presents a significant economic opportunity for local nurseries and landscapers. Many natives that are endangered can have their populations bolstered by use in the landscape. One great example is the current use of Witch Alder (Fothergilla spp.) in the landscape. This is a native plant with many positive aesthetic values that is now rather rare in the wild.
The maintenance of ecological functionality has led to the introduction of many exotic invasives. Many plants have been introduced to prevent erosion and as forage for wildlife. Some examples include Kudzu (Pueraria montana), Lespedezas (Lespedeza spp.), and various members of the genus Elaeagnus. The literature is littered with plants that were introduced for their forage potential. Unfortunately, such plants have a built in dispersal mechanism by birds and other wildlife that may lead to long distance establishment away from the original planting area.
Institutional Framework for Control of Exotic Invasive Plants
All applicable stakeholders need to be involved in exotic invasive control including land managers, conservation associations, federal agencies, universities, horticulturalists, weed scientists, government officials, media, private citizens, local businesses, tourism boards, etc. The exotic invasive phenomenon is too large to be controlled by any one entity. Millions of dollars spent on remediation measures will do no good if plants continue to be dispersed through lack of awareness.
A global invasive species database and early warning system can be found at www.issg.org/database/welcome (Poorter, 2005). The best indicator of potential invasiveness of a species is its invasiveness in a similar habitat elsewhere (Poorter, 2005). Databases from host countries, weed manuals, and plant floras are all useful tools (Ball et al., 2001; Haragan, 1991; L. G. Holm, 1991; Robbins et al., 1970; Royer & Dickinson, 1999; Western North Carolina Tomorrow, 2000).
Campaigns to inform the public about the threat from exotic invasives take on a number of forms. Federal, state and local authorities all produce a variety of materials including pamphlets, brochures, videos, interpretive exhibits, and classes. Nonetheless, much is left to be done to educate the public about the challenges faced regarding exotic invasives. The Department of Transportation in North Carolina published a guide about exotic invasives that may serve as a model for other areas (C. Smith, 2008). There is a campaign in the community of Sandy Mush near where i live to come together for the removal of invasives. What organizations around you are doing this kind of work? Write about them in the comments below or on Facebook is you can.
Pest Risk Analysis (PRA) is one tool under the banner of the International Plant Pest Convention (IPPC). The IPPC was signed by the United States and is administered under the Food and Agriculture Organization (Andow, 2005). The implementation of IPPC rules has led towards a presumption of safe until proved otherwise. Therefore, PRA’s must be conducted in a timely fashion to head off possible pest problems before they become an overwhelming issue.
The National Park Service of the U.S. also has a qualitative risk assessment tool. Their models use a point scale to rank a species potential for invasiveness, cost of control, and the consequences of delay. All these factors are combined to determine which organisms should be prioritized for management (Andow, 2005). National parks are constantly under threat from exotic invasives due to their large size and especially diverse habitats.
Many other entities within the U.S. government do work concerning exotic invasive plants. The U.S. Department of Agriculture’s, Animal and Plant Health Inspection Service (APHIS) is responsible for the prevention of the introduction of foreign weeds. They work to eradicate introduced pests and regulate the importation of potential invasives. The Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW) is a group of 17 organizations dedicated to determining ecologically sound ways to manage invasive plants on federal and private lands.
Regional research centers can possibly offer the resource of limited introduction as an intermediate step in assessing if a problem may arise. This type of research is very time consuming and somewhat limited by definition. For instance, a species may respond differently under various conditions of soil types, nutrient regimes, and climate that are hard to replicate. Nonetheless, research is necessary to justify appropriate rules and regulations concerning exotic invasives. The Southeast Early Detection Network is a regional resource to help reporting across different interest groups and agencies the invasion of plants but also wildlife, insects and diseases. There is now also an Early Detection and Distribution Mapping System set up by various chapters across North America.
Tools of Control
Prevention is the cheapest and most effective means of exotic invasive control (Westbrooks, 1998). One aspect of prevention is education and the North Carolina Invasive Plant council has a host of resources for teachers including videos, games, articles and songs!
Other types of control include mechanical, chemical, burning, and biological. (Di Tomaso & Johnson, 2006; Kaufman & Kaufman, 2007; Miller, Manning, & Enloe, 2010; K. Moore & Hyland, 2002; Wikeem, 2006).
Practitioners must first decide where to focus efforts. They need to decide whether to concentrate on outlying areas in which invasives are spreading or look to areas of particular biological interest. Economics are also a key factor in deciding control strategies. Ultimately an Integrated Pest Management (IPM) strategy is the most effective means of controlling exotic invasive plants (Chace, 2013; Clout & Williams, 2009; Miller, 2007; Morris, 2009; Myers, 2003). IPM is a holistic approach to managing pests taking into account economic, environmental, and social implications of infestations.
Mechanical control can be a useful practice though it is typically employed in partnership with responsible herbicide use for larger scale invasions (Miller, 2007). Brush cutting can allow for the treatment of plants basally and of the more susceptible tender re-growth. Use of various disking implements and rakes may only serve to propagate certain asexually reproducing species. String trimmers may be used to wound waxy leaves and provide for more effective herbicide uptake. Repeated application of mechanical techniques such as brush cutting and mowing can eventually exhaust the re-growth potential of some plants such as Multiflora Rose (Rosa multiflora) (Kay, Lewis, & Langeland, 1995). Girdling and mulching are two other mechanical techniques that are effective with certain species.
Herbicides should be the last resort, but are sometimes necessary for heavy infestations of particular species. Judicious use of the least persistent, most effective, and environmentally friendly herbicides is therefore sometimes warranted (Randall & Marinelli, 1996). A number of methods are used with the application of chemical herbicides. These include foliar sprays, stem injection, cut-treat, basal sprays, and soil spots. Care must be exercised when applying herbicides. Responsible applicators uses the right chemical, in the right quantity, at the right time of year, using the right technique and following all precautions as noted on the label.
Organic herbicides do exist. They are mostly based on high concentrations of vinegar often in concert with other botanical oils (Abouziena, Omar, Sharma, & Singh, 2009; Brainard et al., 2013; Cai & Gu, 2016; G. J. Evans & Bellinder, 2009; G. J. Evans, Bellinder, & Hahn, 2011; Glenn J. Evans, Bellinder, & Goffinet, 2009).
Much research has being conducted on the use of biological controls for exotic invasives (Callaway, DeLuca, & Belliveau, 1999; Coombs, Clark, Piper, & Cofrancesco, 2004; Ding et al., 2006; Dufour, 2000; Hinz & Schwarzlaender, 2004; Hoddle, 2004; Keane & Crawley, 2002; Louda, Kendall, Connor, & Simberloff, 1997; MacKinnon et al., 2005; Markin, 1991; Messing & Wright, 2006; Pearson & Callaway, 2003; Schat & Verkleij, 1998; Simberloff & Stiling, 1996; Van Driesche, 2002; Zheng, 2005).
Scientists will often go to the home range of an introduced plant and observe its natural predators. Caution must be used before large scale introduction of such predators. The possibility of unexpected deleterious side effects from biological predator introduction needs to be assessed first. Biological controls also need to be as target specific as possible.
Multiflora rose (Rosa multiflora) presents an example of a biological control success story. One disease and two insects are now preying on multiflora rose and are expected to largely control it eventually (Amerine, 2000). It remains to be seen if these predators will move onto native roses when and if the exotic invasive one becomes eradicated. Some people also use animals such as goats to control invasives such as Kudzu, Multiflora rose, and other brambles (Kay et al., 1995). Other friends of mine feed their goats Privet (Ligustrum sp.). Care must be taken, as animals can also be vectors for the spread of invasives if they consume fruits which produce viable seeds post digestion (Miller, 2007).
Many exotic invasives have uses in their places of origin. Some of these plants are used for food, medicine, and crafts. Harvesting for use may become another method of deterrent if the general public can be encouraged to take up some of these traditional practices. This phenomenon would essentially create a resource from a menace. i presented research on this idea for the 2008 Society for Economic Botany Conference held at Duke University. A recent publication by Timothy Lee Scott (2010) does an excellent job of exploring the potential of invasive plant medicine in particular. A website www.alienweeds.com covers many aspects of using invasives for crafts. Nancy Gift (2009), who is a Harvard and University of Kentucky trained Weed Scientist in her book A Weed by any other Name also speaks vividly about the “virtues of a messy lawn”. Authors Fred Pearce (2015) and Tao Orion (2015) have also jumped on the band wagon of reframing our relationship to these organisms and how we characterize them.
My research shows that a significant amount of exotic invasives can be used for food, medicine, crafts and more. i have recorded a total of 123 species out of 300 species listed as invasive by SC, NC, KY, VA, TN, and GA to have some potential use. Fifty-six species listed as top priority by at least one of these states has a potential use. The large majority of plants with a use can be employed for food, medicines, or natural dyes (Buchanan, 1995; Cannon & Cannon, 2003; Couplan, 1998; Duke, 1992; Duke & Foster, 1999; Peterson, 1978). Kudzu is one example of an exotic invasive plant that can be used for all manner of applications including food, medicine, fuel and fiber (Baldwin, 2003; Benlhabib, Baker, Keyler, & Singh, 2004; Forseth & Innis, 2004; Hoots & Baldwin, 1996; Keung & Vallee, 1998; Penetar, Toto, Lee, & Lukas, 2015; Shebek & Rindone, 2000; Shurtleff & Aoyagi, 1985).
The exotic invasive literature rarely if ever addresses these potential uses or their possibility as a means of control. i hope to help rectify these omissions as time goes on. You can see the list at the following http://www.botanyeveryday.com/resources?expand=19.
A number of websites have also taken on the task of featuring the employment of exotic invasives for various uses including Eat the Invasives, Invasivore, and Forager’s Harvest. i am particularly fond of the art work of Patterson Clark featured at Alien Weeds.
Further Research with Exotic Invasives
Further research might focus on a variety of questions. What is the economic and social viability of pursuing identified uses? How effective are harvesting practices in relation to controlling target species? What other uses might be identified? What is the correlation between form of plant and area affected? What are the relations between major invasive families and genus diversity? What is the most effective means to pursue notification and conversation with various regulatory bodies to align invasive categorization and treatment prioritization? Global climate change also seems like it will possibly contribute to the spread of exotic invasive species (Clements & Ditommaso, 2011; Mooney, 2005; Rahel & Olden, 2008; Thuiller, Richardson, & Midgley, 2007; Ziska, Blumenthal, Runion, Hunt, & Diaz-Soltero, 2011).
The role of exotic invasives in Appalachia might be studied through the Appalachian Plant Materials Center. The Southeast which includes most of southern Appalachia has over 300 species considered as exotic invasives. The field of exotic invasive control needs further studies to determine the full economic impact of exotic invasives. These types of studies would help justify the expense of control efforts and the prevention of further infestations.
Lists of possible native analogues for various areas need to be further compiled. Dr. Sunshine Brosi made the point to me that the ability to distinguish between natives and exotic invasive relatives is also important. A couple guides have pointed out exotic invasives and their native look alikes (Maine Volunteer Lake Monitoring Program, 2007; Sarver, 2008). Good natured people trying to control invasives may instead remove their often rare and threated native relatives by accident i.e. native Bittersweet (Celastrus scandens) while trying to remove Oriental Bittersweet (Celastrus orbiculatus). As an aside, i learned at an international ethnobotany conference that Oriental Bittersweet is consumed as food in at least one part of China (Kang, Łuczaj, Ye, Zhang, & Kang, 2012). However, i would state that this same community consumes other plants known to be dangerous if not toxic and the Bittersweet family (Celastraceae) is typically not consumed for food as far as i know. Dr. Brosi also brought to my attention the fact that support of exotic invasive uses can sometimes have unforeseen deleterious consequences (Nuñez, Kuebbing, Dimarco, & Simberloff, 2012).
Another thing to think about regarding conservation biology is using as local as possible plant material for native species planting as seed or propagules from afar are in essence genetically exotic albeit on a smaller scale than plants from further afield. A factor which is an especially important consideration if the species worked with is rare in distribution.
Nurseries can be engaged to fill the niche of native plant production. A number of resources exist to help this practice (Bir, 1992; Burrell, 2006; Cullina, 2000, 2002; Foote & Jones, 1989; Harper-Lore & Wilson, 2000; North Carolina Wild Flower Preservation Society, 1977; Tennessee Valley Authority, 1998). Prairie Moon Nursery is one of my favorite seed suppliers though their genotypes might be from outside the Appalachian region. Native plant growers can also supply material for the re-vegetation of public natural areas.
Hopefully, this information on exotic invasive plants has empowered you to be more aware of what you might introduce to the area where you live and how you might help control the exotics that are already running rampant across the land.
For the next class we will cover major Medicinal plant families. The class will be posted around September 15th.
Below are items to think about/comment on. Please write me directly at firstname.lastname@example.org or leave information in the commentary under this class.
i WOULD REALLY LOVE TO HEAR WHAT YOU HAVE TO SAY!!!
- Do some research into the utility for invasive plants around you and share that info with some people
-Do your part to remove some exotic invasives from a sensitive area either alone or in partnership with a local organization
- Plan a fall garden
- Attend a workshop or a class and write up a brief description of plants or information learned.
- Post any clear photos of question plants to Facebook or send in an email.
Praises to all that have donated to the cause. i encourage everyone reading this to donate as they are able financially, commentarialy, or energetically... Your contributions greatly help me continue this crucial work of ethnobotanical research and education. Please let me know your thoughts in general and anyway i can help this class serve you best.
Here’s a great map to see a visual representation of the relative infestation of invasive plants in the U.S. from the Forest Service
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