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The native fescue grassland that has characterized the foothills region of southwest Alberta is highly adapted to the climate, provides excellent winter grazing for both wildlife and domestic cattle, stores significant amounts of organic carbon in the soil, and is an outstanding watershed cover. The loss of native grass poses a serious threat to the viability of this range ecosystem. An important reason for this loss is from the invasion of non-native alien plant species that can out-compete the fescue grass in the short-term. They also reduce the multiple uses and values that range is normally capable of providing.
Invasive alien plants are introduced plants that grow, spread and take over a new habitat beyond their natural range. They are usually introduced inadvertently by human activity. These plants threaten the environment and the economy, and can be extremely damaging to native fescue grassland. Local municipal districts spend considerable time and money in control programs. An example of a restricted plant is the spotted knapweed (Centaurea maculosa) illustrated to the right.
There are several categories of such weeds: restricted, noxious, nuisance, and others. All of these create various degrees of threat, and all of them are difficult to eradicate.
- Restricted: Restricted weeds are usually found in small numbers, and are designated as restricted in order to prevent their establishment. Restricted weeds are non-native species that pose a serious threat because of their ability to spread rapidly and out-compete natural vegetation.
- Noxious: Noxious weeds are generally more abundant than restricted weeds. They have the ability to spread rapidly.
- Nuisance: Nuisance weeds are common throughout the Province, and are often native species. Due to their abundance and biological suitability, it is difficult to eradicate nuisance weeds.
- Other: There are a number of other problem plants which may not be currently designated under the Alberta Weed Control Act, but may be categorized by various municipalities or municipal districts as noxious or nuisance.
Weeds are seldom a problem in a vigorous, healthy, and well-maintained rangeland although they may be introduced through rodent burrows. The presence of non-native weeds usually indicate the presence of a degrading plant community where poor grazing practices or inappopriate human activity has resulted in available niche space (bare soil, surplus moisture); available micro-habitats normally occupied by range plants.
Prevention practices are critical to proper range management. This is especially applicable in the fescue rangeland due to the difficulty of re-establishing a healthy fescue community. The key practices include the following:
- Education: Awareness programs that alert people to the real damage done by invasive alien plant species is critical, especially for people using the landscape for industrial and recreational purposes. Rural acreage landowners sometimes introduce weeds to domestic gardens because they look 'nice'.
- Limit Soil Disturbance: Any time that the ground is broken for agricultural, industrial, or recreational reasons it provides opportunity for weeds to proliferate. Minimize such activity on native fescue rangeland to zero if possible. Ensure that weed issues are part of any industrial project planning.
- Clean Equipment and Vehicles: One of the major vectors of weed introduction is on industrial and recreational vehicles. Weeds come embedded in dirt, mud and tires. High-pressure spray cleaning of equipment and vehicles should be done prior to entering (and far away from) any native rangeland.
- Avoid seed introduction in Materials: Weed seeds can be introduced in aggregate fill, hay and straw bales, and feed. If in doubt attempt to source only from certified weed-free sources.
- Early Detection and Action: Detection of weeds before they can propogate seeds is critical. Many invasive weeds put the majority of their energy into seed propogation (high reproductive capacity). Early control procedures including hand-pulling can avoid the use of large amounts of chemicals later. Training local people and staff to recognize weeds and how to remove them is of great value.
- Revegetate: Any disturbed ground should be reseeded with an appropriate seed mix in a timely manner. Any opportunistic weeds must be removed by hand prior to seeding. There is a good chance that several years of weed control will be required to ensure that a healthy fescue rangeland is re-established.
- Communication: Communicate and work with your local municipal district agriculturalist. They will be more effective if they know what is happening on your land.
Control strategies can be complex, balancing the impacts of invasive weeds against the economic realities of control. Methods typically include hand-picking and the use of chemicals. On introduced (tame) pasture it may involve tilling.
Another example of a restricted plant, nodding thistle (Carduus nutans), is illustrated to the right.
Selective grazing by sheep has sometimes been used successfully to control weeds.
There are many sources of information on invasive weeds and control methods. In Alberta the Weed Control Act applies. The Act is administered by the Department of Agriculture, Food and Rural Development. The enforcement of the Act is delegated to local municipalities. This Act over-rides any other legislation dealing with weeds, and the Crown is bound by it.
Links to relevent other websites include:
Weed Act - Alberta
ASRD Weed List
AFRD Weed List and FAQ
Agricultural Fieldmen: Southern Region
Invasive Alien Species - Hinterland Who's Who
Environment Canada Invasive Alien Species Strategy
Team Leafy Spurge - USDA
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