CBCN Newsletter
Vol. 2, N. 1 -  August 1997

Invasive Plants: A Key Biodiversity Issue

The risk to intact natural habitats posed by invasive plants has emerged as a key concern for the conservation of our native biological diversity in Canada.

Botanical gardens have been identified as a source of invasive plants in the past. Expanding awareness of the risks posed by invasive plants and the programs already available to minimize those risks is an important component of biodiversity education.

This issue of our newsletter is devoted to the invasive species problem.

What Makes a Species Invasive?

A variety of schemes are in use which classify plants into categories to describe their relative impacts if they escape from cultivation. Here are some general definitions:

Native Species

Any species which was growing in Canada prior to the arrival of European settlers. We have about 3200 species of native plants in Canada.

Complicating the definition of "Native" is the fact that species which are native to a particular geographic region - like Canada - will not be native to habitats other than their original settings.

Alien Species or Exotics

Any species which has arrived in Canada since the beginning of settlement by Europeans is an alien. This category is usually only applied to plants growing in natural or seminatural areas.

Naturalized Species

An alien species that has adapted to life outside of cultivation and has become self-perpetuating without human intervention. We have about 800 species of naturalized aliens in Canada, most of which cause little damage to intact natural habitats.

Invasive Species

Some naturalized species have life-history characteristics that make them able to colonize and spread rapidly in intact natural habitats. Invasive aliens share several life-history characteristics that enable them to be very effective competition to native species in intact habitats.

The Invasiveness Scale:

A scale of invasive risk has been established for species that have been well studied or whose range is well determined. The invasive categories are as follows :

0 - not weedy or invasive

1 - Minor weed of highly disturbed or cultivated land

(man-made artificial landscapes)

1.5 - Serious or widespread weeds of 1

2 - Weeds of pastures managed for livestock, forestry

plantations or artificial waterways

2.5 - Serious or widespread weeds of 2

3 - Invading seminatural or natural habitats (some

conservation interest)

3.5 - Serious or widespread invaders of 3

4 - Invading important natural or seminatural habitats (i.e. species-rich vegetation, nature reserves, areas

containing rare or endemic species)

4.5 - Serious or widespread invaders of 4

5 - Invasion threatening other species of plants or animals with extinction

The invasive categories were compiled from the 'People and Plants' Conservation Manual Plant Invaders : The threat to natural ecosystems by Quentin B. Cronk and Janice L. Fuller.

Invasive Plants Alert: Local Actions for a Global Problem

An Invasive Plants Alert (IPA) program has been initiated with funding from the Biodiversity Convention Office, Environment Canada. This is part of the on-going activities of the Invasive Plants of Canada Project (IPCAN) that was established two years ago through support from several federal agencies. IPCAN was established for compiling information on the biology, range and control of invasive exotic plants and for developing databases for computer mapping and analysis.

The purpose of the IPA initiative is to promote local actions by naturalist clubs and other groups, to study, monitor and control invasive alien plants. There are many other alien species, other than the well-known purple loosestrife, that have significant impacts on native habitats and species. Because of the number of species and extent of the problem of alien species altering the natural composition and development of native habitats, participation by a wide range of interested naturalists, biologists and conservationists is required.

With the assistance of the Canadian Nature Federation, affiliate clubs across Canada are being asked to participate in this effort to stem the spread of invasives. Other groups that are considering similar actions at the provincial level are also being contacted to facilitate a co-ordinated approach. Naturalist clubs, trail associations, conservation groups, botanical gardens and the horticultural communities can all assist in stemming the spread of alien species. Local control actions by interested clubs and individuals can be effective in reducing population sizes of well-established invasives in areas of significant natural history value. It is such natural areas that should be the main targets of control actions. As well, through monitoring of local areas and prompt actions to eradicate newly established invasives, the development of dense areas of local infestation can be prevented, thereby reducing the rate of spread of alien species.

The IPA program provides an information package that is sent by the co-ordinating office to club representatives who have agreed to serve as the contact for their group. This package includes information on species of particular concern within the province or region where a club or group resides. A monitoring guide, prepared with naturalists in mind, has been completed for Ecological Monitoring and Assessment Network (EMAN), Environment Canada. This is also available to those interested in more than just reporting occurrences of significant populations of alien plants. The guide provides insights into the kinds of studies that can be undertaken by an interested individual to demonstrate the spread and impact of invasive plants within natural habitats. Even the reporting of significant infestations and newly arrived alien plants within an area, however, is a valuable contribution towards national efforts to control the spread of invasives. Reports of invasive plant occurrences that are sent to the IPA co-ordinating office are entered into the national databases being compiled as part of the IPCAN project.

An important constituent of the Alert program is the IPA Bulletin. This is an Internet information noticeboard for short articles and interesting observations dealing with the biology, monitoring and control of invasive plants in Canada. The Bulletin is a forum for promoting local group activities and for providing information that may be of help to others wishing to take actions. Short information articles should be submitted to the IPA co-ordinator, preferably as e-mail messages or digital file attachments. Printed paper copies will also be accepted. Information notices on such topics as the following are of particular interest: significant local and regional infestations that have already or may potentially invade natural habitats, newly-arrived and spreading invasives, impact on the local flora and fauna of infestations and control actions and results of activities. Further information about the IPA program and the IPA Bulletin is available from the co-ordinator and is also on-line at:

http://infoweb.magi.com/~ehaber/ipcan.html

Invasive Plants of Canada

The most troublesome or aggressive weeds are those foreign or alien species that have invaded the North American continent from regions elsewhere in the world. By comparison, fewer and less aggressive weeds are native species. The distinction between foreign species and native species is not always clear, and it is not easy to measure the impact of those foreign or alien plants on the native vegetation.

Foreign or alien species are usually regarded as those that have been brought to North America by human activities in post-Columbian times, while native species had arrived by various means in pre-Columbian times. How many species have been transported from their place of nativity to North America in post-Columbian times is unknown.

Many species arrived in North America accidentally, through packing materials, hay, and animal fodder, or in the ballast of ships, while others were purposely introduced as ornamentals, for cooking, or for medicinal uses. Many of the purposely introduced species managed to escape from cultivation, and due to rapidly changing land use, managed to spread widely. This continued change in land use, coupled with the spread of population, has made it possible for invasive species to increase their range, sometimes to the extent that they crowd out native species and threaten natural habitats. Some species that are considered invasive are still commercially available and are found in many gardens across Canada.

Some invasive species have spread to the extent that they have begun to threaten the existence of endangered native species. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) have indicated that in Ontario, garlic mustard (Alliaria petiolata) has been cited as a threat to the endangered wood poppy (Stylophorum diphyllum) and the threatened white wood aster (Aster divaricatus). In Alberta and Saskatchewan, the endangered slender mouse-ear-cress (Halimolobos virgata) is being threatened by the invasion of crested wheat grass (Agropyron pectiniforme) which has reduced the habitat available for and the number of populations of the native grass species.

There are three basic types of plants found as invasive in Canada. These are Trees, Shrubs/Vines, and Herbaceous species (includes Wetland species). These species flourish in a diverse number of habitats, ranging all across Canada. The majority of exotic species found in Canada are European and Eurasian in origin. Many of these species share the same characteristics, such as rapid growth in a variety of conditions, abundant seed production, highly successful seed dispersal, germination, and colonization, the ability to propagate vegetatively, a lack of pests or pathogens acting as natural controls, the ability to out-compete native species, and a high cost to remove and control.

In order to increase public knowledge of the dangers of invasive species, the Canadian Botanical Conservation Network has prepared a comprehensive list of invasive species found in Canada, including a description of each species and control methods for small scale invasions. Large infestations may require that more drastic measures are taken to ensure removal of the invasive species.

Though some species that are considered invasive may be beautiful, they can pose a threat to native vegetation and natural habitats, and in most cases, a native plant with many of the same characteristics may be available to replace the exotic species. Many people choose exotics for the beauty of the plant, but many of these aliens are hardy, disease free, have few if any insect pests, and reproduce or propagate easily. Unfortunately, these characteristics make them serious competitors when they are released into a new ecosystem or habitat.

When choosing plants for your garden, determine whether they are native or exotic. Learn what native species can be used in place of exotics - there is almost always an equally attractive alternative.

Highly Invasive Species

Listed below are eleven species that are considered highly invasive problem species in Canada.

• Allaria petiolata Garlic mustard, Hedge garlic
  

• Celastrus orbiculatus Oriental bittersweet, Asiatic bittersweet
  
• Cynanchum nigrum Dog-strangling vine, Black swallowort
  
• Elaeagnus umbellata Autumn olive
  
• Euphorbia esula Leafy spurge, Wolf's milk, Faitours grass
  
• Hydrocharis morsus-ranae European frog-bit
  
• Lythrum salicaria Purple loosestrife, Swamp loosestrife
  
• Myriophyllum spicatum Eurasian water milfoil, Spiked water milfoil
  
• Polygonum cuspidatum Japanese knotweed, Mexican bamboo
  
• Rhamnus cathartica European buckthorn, Common buckthorn
  
• Rhamnus frangula Glossy buckthorn, Black buckthorn

More information on these highly invasive species, and on other species that are considered invasive can be found by accessing the Invasive Plant List. The Invasive Plant List prepared by the Canadian Botanical Conservation Network is available online.

Membership In CBCN

We are pleased to announce that organizations and individuals are now invited to apply for membership in the Canadian Botanical Conservation Network. Canadian botanical gardens and arboreta may join CBCN as full members. Individuals and other organizations may join as associate members. Several organizations have already taken the step to join the network, including:

• The Arboretum, University of Guelph, Guelph, ON
  

• Brickman's Botanical Gardens, Sebringville, ON
  
• The Civic Gardens Centre, North York, ON
  
• Metro Toronto Zoo, Scarborough, ON
  
• Niagara Parks Botanical Gardens, Niagara Falls, ON
  
• Royal Botanical Gardens, Hamilton, ON

For more information on membership, please contact the coordinator at the address below.

The CBCN Web Site Moves!

We have upgraded our Web site once again, and are in the process of moving to a new server. The Canadian Botanical Conservation Network site on the World Wide Web has been moved to:

http://www.rbg.ca/cbcn

The revised site has been redesigned graphically to improve the speed of access and the appearance, and new articles have been added. Of particular interest may be the new pages on invasive plants, prepared by CBCN Summer Research Assistant Melinda Thompson. As always, we welcome feed-back or contributions to the Web site and the newsletter.

The CBCN Newsletter is produced by the Botanical Conservation Office of Royal Botanical Gardens on behalf of the Canadian Botanical Conservation Network. For more information on CBCN, please contact:

Dr David Galbraith
Coordinator
Canadian Botanical Conservation Network
C/O Royal Botanical Gardens
P.O. Box 399
Hamilton, Ontario L8N 3H8
Canada