Blog & News

By Simon Wilmot

Invasive plant species are among the leading threats to native wildlife and species-at-risk on PEI, displacing native species, reducing local biodiversity, altering food-web structures and changing how ecosystems respond to disturbance. Below we have highlighted some of the impacts invasive plants species have on wildlife and biodiversity on PEI to demonstrate the importance of prevention and management efforts. 

Invasive Plant Impacts on Food Webs  

A number of PEI species at risk are insectivores including little brown myotis (Myotis lucifugus), northern myotis (Myotis septentrionalis) , eastern wood-pewee (Contopus virens) common nighthawk (Chordeiles minor) and the olive-sided flycatcher (Contopus cooperi) and therefore are susceptible to declines in invertebrate species. Invasive plant species reduce the diversity, abundance and taxonomic richness of terrestrial invertebrates at heavily invaded sites. Declines in invertebrates reduce the availability of resources for insectivores negatively impacting populations of insectivore species. 

Monarchs are particularly vulnerable to the impacts of invasive plants displacing nectar plants and swamp milkweed. There are a number of invasive species that threaten monarch habitat currently on PEI, however, the most significant threat comes from dog-strangling vine (Vincetoxicum rossicum) currently not present on PEI but present in Nova Scotia.  The vine threatens the monarch butterfly due to its similarity in appearance to swamp milkweed leading to butterflies laying their eggs on the plant. Monarch larvae are unable to complete their life cycle on the vine and do not survive.

Monarch Butterfly on Swamp Milkweed, Beth Hoar, Green Thumb Photography

Threats to Riparian Areas

Invasive plant species are a significant threat to the ecological integrity and ecosystem services provided by riparian areas. Invasive species can alter nutrient cycling, hydrology, erosion rates, food webs and energy budgets in riparian areas and reduce biodiversity. Critically for fish species, changes in riparian vegetation can have cascading impacts through the terrestrial-aquatic interface, disrupting terrestrial inputs to aquatic food webs. 

Dense stands of riparian invasive species such as knotweeds (Fallopia sp.) and giant hogweed (Heracleum mantegazzianum) inhibit the  establishment of woody plants and floodplain trees, such as black ash (COSEWIC threatened species). Eventually, heavily invaded riparian areas are transformed from diverse ecosystems to herbaceous monocultures or ecosystems with little diversity that are unable to sustain native wildlife.

Giant Hogweed Control, Queens County, PEI:  Nicolas Bergeron, Pisquid River Enhancement Project and Hillsborough River Association

Purple loosestrife is another invasive species impacting riparian areas and wetlands on PEI. This  emergent, perennial riparian plant is common on PEI,  fast-spreading and can cause local reductions in native plant species by richness displacing native sedges, cattails and other plants. It can also cause seasonal shifts in the availability of local nutrients in water bodies due to varying decomposition rates  compared to native riparian species. Purple loosestrife can also impact wetland hydrology, severely impacting the significant functions of wetlands such as providing breeding habitat for amphibians and other fauna.

Invasive Plant Threats to Forested Areas

PEI species at risk such as Canada Warbler (Cardellina canadensis), Eastern Wood-Pewee (Contopus virens), Evening Grosbeak (Coccothraustes vespertinus), Olive-sided Flycatcher, Rusty Blackbird (Euphagus carolinus) and various endangered lichen species are dependent on healthy diverse Acadian forest habitat. There are a number of invasive plant species currently present on PEI that threaten these habitats, in particular, Oriental bittersweet (Celastrus orbiculatus), garlic mustard (Allliaria petiolata) and glossy buckthorn (Frangula alnus). Oriental bittersweet and garlic mustard are not widespread, but are present on the island in multiple locations, while glossy buckthorn is common in many areas. 

Oriental Bittersweet 

Oriental bittersweet (Celastrus orbiculatus) is a deciduous, woody vine native to southeast Asia that has become established in various locations across PEI but most significantly in the Georgetown area (See picture to the right).  This vine poses a significant threat to native plant communities and is identified as a high level threat to deciduous, coniferous, and mixed conifer-deciduous forests, old fields, grasslands, riparian areas, and fresh wetlands. With its rapid twining growth, bittersweet climbs over and smothers vegetation as it makes way to the top of the canopy, girdling trees and shrubs as it climbs restricting nutrient and water flow. Weakened and overloaded trees are susceptible to wind throw and loss of limbs.

Oriental bittersweet, Georgetown, PEI, photo by Simon Wilmot, PEI Invasive Species Council 

Garlic Mustard

Garlic mustard (Allliaria petiolata) is a significant threat to forest ecosystems due to its ability to  successfully invade forest understories and become the dominant understorey species. It is also an allelopathic species, producing chemicals in its roots that inhibit the growth of other plants species. These chemicals also affect the growth and regeneration of mycorrhizal fungi that support trees and plants ability to absorb nutrients and water. Recent studies have shown that arbuscular mycorrhizal fungi are almost completely eliminated from the roots of tree seedlings growing in soils where Garlic mustard have invaded. Garlic Mustard is currently present in several locations on PEI, including the Stratford and Cavendish areas. 

Glossy Buckthorn 

Glossy buckthorn (Frangula alnus) is common across PEI forming dense thickets that crowd and shade out native vegetation, transforming ecosystems visually, structurally, and chemically. Glossy buckthorn alters soil characteristics, increasing soil nitrogen, carbon, pH and moisture. Once glossy buckthorn exceed approximately 30 % cover in woodlands it suppresses seedling growth further reducing species diversity and disrupting succession. Glossy buckthorn stands also decreased the recruitment of native shrubs and reduce the diversity of bird foods. 

Early Detection and Rapid Response to Plant Invasions 

The most cost-effective way to manage the potential negative impacts of new invasive species is through Early Detection and Rapid Response (EDRR). Detecting new invaders when they first arrive in an area and then mobilizing rapidly to control and eradicate them before they become well established and start to spread further. The PEI Invasive Species Council (PEIISC) has been providing leadership in the creation of a province-wide EDRR, consolidating existing data on invasive species, launching an observation recording tool, raising public awareness and recruiting volunteers and organizations to map invasive species. 

The PEIISC uses the EDDMapS, or Early Detection and Distribution Mapping System, to record observations and map the distribution of invasive species across PEI. EDDMapS is a digital tool used to across Canada and the US to understand the spread of invasive species.  The public are encouraged to download the EDDMapS app to their smartphone and report observations of invasive species. This data will allow the PEIISC and other conservation organizations to plan and engage in invasive species management activities to protect native ecosystems and wildlife habitat. 

More information:

Becker, R. H., Zmijewski, K. A., & Crail, T. (2013). Seeing the forest for the invasives: mapping buckthorn in the Oak Openings. Biological invasions, 15(2), 315-326.

Bottollier‐Curtet, M., Planty‐Tabacchi, A. M., & Tabacchi, E. (2013). Competition between young exotic invasive and native dominant plant species: implications for invasions within riparian areas. Journal of Vegetation Science, 24(6), 1033-1042.

Casagrande, R. A., & Dacey, J. E. (2014). Monarch butterfly oviposition on swallow-worts (Vincetoxicum spp.). Environmental Entomology, 36(3), 631-636.

Dukes, J. S., Pontius, J., Orwig, D., Garnas, J. R., Rodgers, V. L., Brazee, N., … & Ayres, M. (2009). Responses of insect pests, pathogens, and invasive plant species to climate change in the forests of northeastern North America: What can we predict?. Canadian journal of forest research, 39(2), 231-248.

Mattila, H. R., & Otis, G. W. (2003). A comparison of the host preference of monarch butterflies (Danaus plexippus) for milkweed (Asclepias syriaca) over dog‐strangler vine (Vincetoxicum rossicum). Entomologia Experimentalis et Applicata, 107(3), 193-199.

Wolfe, B. E., Rodgers, V. L., Stinson, K. A., & Pringle, A. (2008). The invasive plant Alliaria petiolata (garlic mustard) inhibits ectomycorrhizal fungi in its introduced range. Journal of Ecology, 96(4), 777-783.