Invasive species

The September 2012 meeting of the PEI Garden Club

Shannon Mader from the Island Nature Trust and the PEI Invasive Species Council spoke about invasive species on PEI.  This is a brief synopsis of her message.

An invasive species is an organism living outside its natural range which causes economic and environmental problems.
Some invasive species present on PEI:


himalayan balsam is related to Jewelweed, a native plant



wild cucumber vine

glossy buckthorn

bittersweet nightshade

Other invasives:

• purple loosestrife - It changes the habitat of ponds.  It is not as pervasive on PEI as it is in other areas.  A biological control has been released here. 
• multiflora rose - widespread
• periwinkle - not widespread - found in Strathgartney Park
• giant hogweed affects human health.  The sap in the stems can burn skin.
• garden heliotrope - white flowers
• field bindweed
• Japanese knotweed

Invasive species suffocate other plants, reduce biodiversity, crowd out diverse species, alter wildlife habitat, change soil chemistry, and can change water levels.  They compete with and can displace native species.  For example, Norway Maple prevents other species from growing close by.  This negatively impacts forests.  It increases fire hazards and decreases the process of regeneration, increases erosion and sedimentation into nearby waterways.

Invasive species affect agriculture.  They reduce crop yield and cause farmers to increase their herbicide use.  It encourages new diseases and the insects that eat the imported plants.

For every 100 introduced plants, 10 will become naturalized, and one will become invasive.  Most imported plants are not invasive. 

Why do some plants spread so rapidly?
The problem with invasives is that there is a lack of natural controls such as preditors, competitors, and disease that are present in their natural environments.  They grow and reproduce quickly.  They can thrive in a broad range of habitats:  shade and sun, dry and wet soil.  They germinate early, produce a great many seeds which are usually small and can travel further.  The seeds survive the winter, or the plants reproduce vegetatively, such as through underground runners. 

How do invasives arrive on PEI?
Many are moved unintentionally.  They can stick to equipment when land is being cleared.    Climate changes have made it easier for some plants to surive here.  Seeds and plants and animals present in ballast water are released far from home. 

Many plants arrive here intentionaly through horticulture, agriculture, and world-wide trade.  Some garden favourites have escaped from gardens and have become a problem in the environment: 

• goutweed
• reed canary grass
• lily of the valley
• creeping thyme
• star of bethlehem
• virginia creeper
• norway maple
• periwinkle
• bugleweed
• oregano
• euphorbia
• creeping bellflower
• false spirea
• water lily
• lady's mantle
• yellow flag iris
• purple loosestrife
• raspberries

Wildflower mixes often contain seeds from invasive species.  Avoid planting invasives.  Dispose of invasives responsibly.  Plant native species.  Don't give away aggressive spreaders.
When purchasing plants, read the descriptions.  Beware of plants which are described as growing in shade and sun, wet and dry soil, and crowding out other plants.
Plant alternatives: ferns, highbush cranberry, serviceberry, sumac, wild rose, wild raisin, red oak instead of English oak

Extra resources
Invasive Species Council of PEI:  http://peiinvasives.ca/pei-invasive-species-council
Global invasive species database
Invasive plants of New England website
Beth Hoar from the City of Charlottetown
David Carmichael from the provincial nursery