About WIGL + FAQs

The WIGL Collaborative uses the two-part definition for invasive species that was established by a federal executive order in 1999. The first part is that a woody invasive species is a species of shrub, tree or woody vine that is not native to the place being considered (in our case, the Great Lakes Basin). The second part is that woody invasive species cause or are likely to cause harm to the environment, the economy and/or to human health. 

Invasive species collaborations are one strategy that the Great Lakes Restoration Initiative (GLRI) uses to implement the invasive species portion of its Action Plan. These collaborations are intended to collect and exchange information on the best methods for controlling invasive species in and around the Great Lakes. Additionally, these collaborations are intended to improve the flow of information from researchers and regulators to land managers (public and private) and to the regulated community. The Phragmites Collaborative was the first of these projects established through GLRI in 2012.

We decided our approach on which species to include through discussion between participating partners. Our initial focus is on 28 woody species that are currently regulated as invasive by one or more Great Lakes jurisdiction. 

Woody invasive species are a problem due to the impacts that they have on the environment, the economy, and/or on human health.

Woody invasive species usually have several characteristics that allow them to out-compete native plants for resources (sun, water, soil nutrients, etc.). In a worst-case scenario, certain woody invasive species will form single-species stands where virtually no other plants grow. Natural areas that are dominated by invasive plants are often not able to function properly as wildlife habitat, particularly for species that are more sensitive to habitat disturbance.

Woody invasive species can cause economic problems, especially in woodlots and managed timber forests where dense growth of invaders can prevent tree seedlings from growing to regenerate the timber stand. Some invasive woody species can cause problems for agriculture either by encroaching onto fields and pastures or by hosting pests that can damage crops. Where they grow very thick or tall, woody invasive species can pose a hazard along roadsides, utility corridors, and even hiking trails, costing money to manage.

Finally, although none of our initial focal species are acutely poisonous to people (though we don’t recommend you eat the berries of most of them!), they can harm human health in other ways. Some species of invasive shrub provide extra cover and for mice, which play an important role in the life-cycle of the ticks that carry human diseases. By managing invasive plants, we can make forested areas less hospitable to ticks and safer for human visitors. 

Everybody can take care not to spread the seeds woody invasive species by cleaning their boots and any other equipment and animal companions after visiting a natural area. You can pledge to take this important precaution through our friends at PlayCleanGo!

Everybody can learn to identify invasive woody species and report them using EDDMapS (all locations), iMapInvasives (NY & PA), or MISIN (MI).

Homeowners and commercial site managers can avoid planting woody invasive species. There are so many amazing alternatives; there is really no need to! Site managers can also remove any existing woody invasive plants on their property and replace them with alternatives.

Municipal officials can remove any invasive species from their community’s street tree list or park planting list.

Nursery and garden center managers can phase out the production and sale of non-regulated woody invasive species on a voluntary basis. Local businesses may even benefit from forming partnerships with local invasive species groups to coordinate buy-back or exchange programs for target species.

The truly dedicated can volunteer at local natural areas to help manage woody invasives. Look up your local land trusts, forest preserves, park districts, etc. Most could use the help!

Everybody can tell their friends!

Every species is different, but there are traits that are common in invasive woody plants. Woody invasives often:

• Produce a lot of seed each year
• Grow quickly compared to native plants
• Reach sexual maturity relatively quickly
• Leaf out earlier in the spring and lose leaves later in the fall compared to native plants
• Are able to rapidly colonize areas after disturbance (flood, fire, land clearing, etc.)
• Produce seeds that are readily dispersed by birds, wildlife and/or people
• Reproduce vegetatively as a primary or secondary mode of reproduction
• Are adapted to a broad range of soil and/or light conditions
• Display high genetic variability
• Live in close association with humans

Almost all of our focal species were brought to North America as garden plants. Often, they were introduced hundreds of years ago, long before the concept of invasive species was developed and before anyone was aware of the potential impacts on native biodiversity. It is important to note that botanic gardens and plant breeders still import ornamental plants, though are hopefully doing so with a greater awareness of the invasive species risks. The Midwest Invasive Plant Network (the WIGL Collaborative’s founding partner) is currently working with public gardens to improve monitoring and information sharing on recently imported plant species.

There are a number of different ways invasive plants can spread. People have purposefully planted many of our focal species in new places – sometimes in their gardens and sometimes along highways for erosion control or between farm fields as wind breaks. People can also accidentally move seeds from place to place on their clothing, animals or vehicles after hiking, horseback riding or off-roading in an infested area. 

Many of our focal species are moved from place to place by birds and other types of wildlife which eat the fruits or seeds and deposit them elsewhere. Birds may contribute the most to this problem because their flight allows them to travel greater distances and to move invasive plant seeds further away from their source.

The seeds of some woody invasive species are moved from place to place by wind or in moving water.

Not necessarily. There are a number of factors that impact where a plant species can grow and where it can reproduce successfully. These include hardiness (a plant’s ability to withstand cold winter temperatures), light requirements, soil requirements, exposure to pests and diseases, and competition from other plants. As you look at the distribution information in our species profiles, you will see that certain parts of the region, particularly northern Minnesota and the Upper Peninsula of Michigan, have fewer reported woody invasive species than the southern parts of the Great Lakes watershed. This is likely at least partially due to hardiness – these are the coldest parts of the region. 

Another consideration is that many invasive woody plant species thrive in disturbed areas such as abandoned lots, retired farmland, forest edges, urban parks, transport and utility right-of-ways, and stream banks. Invasive woody species may not be able to compete as effectively in high quality natural areas, where native plants are long established. However, this is definitely not a hard rule. Invasions often start on the edges of natural areas, but over time birds and animals spread seed to interior areas.

“Cultivar” is a combination of the words “cultivated variety.”  A cultivar of a plant species has been specially bred by plant biologists or horticulturalists to improve the plant in some way. A cultivar will usually share many characteristics with the species, but will have certain traits that are different. Some cultivars are bred to be more attractive than the species, while others are bred to resist pests or diseases. Cultivars are sold at garden centers and online under trade names that usually appear in quotation marks or with a trademark symbol. If you’ve ever encountered a plant tag with a catchy name like ‘Hello Dolly’ or ‘Hot Cocoa’, that’s a cultivar name.

Cultivars are important in invasive species discussions because they can have more or fewer invasive characteristics than the species. In some cases, plant breeders have worked to develop cultivars of invasive woody species to make them less invasive. These cultivars generally produce less seed than the species and, in some cases, produce virtually no viable seed. Reduced fertility and sterile cultivars are a hot topic because there have been cultivars developed in the past that were promoted as sterile, but that have gone on to successfully reproduce and contribute to invasive species populations. While reduced fertility cultivars are not a “silver bullet” for woody invasive plant issues, we have presented scientifically supported information about low-seed and sterile cultivars in our species profiles where it is available.

Nurseries and garden centers develop, stock and sell certain invasive species and their cultivars because there is a demand for them in the market. Some invasive species are popular in gardening and landscaping for having relatively unique aesthetic qualities (e.g., the brilliant red foliage of winged burning bush or the symmetrical up-right shape of Callery pear). Some invasive species are popular for being tolerant of poor conditions or requiring little maintenance. Others may attract birds or wildlife.  In some cases, state governments have banned the sale or planting of certain woody species known to be invasive. You can view our species profiles or visit our regulatory information page to learn more.