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Western Blue Flag

Limiting Factors

Western Blue-flag Much of the Foothills Fescue Grassland and Parkland has been brought into cultivation or otherwise modified. This, combined with the fact that plants have a number of characteristics distinct from those of animals that must be factored into any program aimed at their conservation means that processes such as habitat alteration and fragmentation thus have direct consequences to plant populations. 

The endangerment of plant species is usually attributed to one of four things: overexploitation, habitat loss, competition of non-native species or spread of disease. Threats to small populations fall into three categories: genetic (loss of genetic variation and hence ability to adapt), demographics (unpredictable changes in population sizes, composition, etc.) and environmental. Genetic and demographic threats increase with a decrease in the population size while environmental threats can be independent of population size. 

Habitat Loss, Alteration Fragmentation:  Western blue flag probably never been common in Alberta given that it is at the northern edge of its range and that it has specific habitat requirements. Its historical range is difficult to determine because information on its occurrence is not found in the literature, prior to 1964. However, it is likely that alteration of habitat within its distribution has resulted in the loss of some pre-settlement populations. Fescue-dominated systems, grassland and parkland, where western blue flag occurs are among the most threatened regions on the Canadian plains. Somewhere between 85 to 95% of the Parkland Natural Region has been lost through activities such as cultivation and urbanization. Some of the greatest losses of native prairie have been in the Foothills Fescue Grassland. Wetlands in the grassland systems have also been under intense pressure from being drained and filled. Estimates of loss of grassland in Alberta are 63% in the White Zone.

Competition from Introduced Species: This is an increasing threat to native flora and fauna. Indeed, smooth brome is out competing western blue flag at a rapid pace in at least one of the known native occurrences, Police Outpost Provincial Park. Competition from introduced species remains a potential threat at sites other than Police Outpost Provincial Park as well.

Grazing: Eradication of western blue flag from native grasslands in Nevada was actively promoted in the 1970s. This occurred because western blue flag is unpalatable to livestock and may cause poisoning. It is unknown whether native populations of western blue flag have been actively removed for similar reasons in Alberta. Heavy grazing pressure appears to have a negative impact on western blue flag both in Alberta and North Dakota. Both Wallis. The main effect of grazing on western blue flag may not be due to grazing of the plant itself but rather to alteratic drainage patterns and hydrology resulting in trampling. 

Conversely, lack of grazing may also be a limiting factor. The population at Police Outpost Provincial Park is not subject to use by cattle and plants appear to have reduced levels of flower production. It is uncertain whether this is attributable to lack of grazing or to other factors.

Alteration of Hydrology:  Changes in hydrology constitute a limiting factor at both the Whiskey Gap and Police Outpost locations. At the Whiskey Gap location, western blue flag occurs just below a seepage area. Cattle congregate in the vicinity of this seepage, causing trampling of the plants and diversion of water.

The population of western blue flag at Police Outpost Provincial Park is near the shore of Outpost Lake. Water in the lake is replenished from springs and precipitation, as there is no inflow stream. The stream draining the lake has an outflow structure across it that was built to maintain water levels high enough to prevent winterkill of sport fish in Outpost Lake. During periods of abundant precipitation, water levels in the lake are high enough to flood out a portion of the population of western blue flag.

Horticultural and Medicinal Uses:  Western blue flag is also threatened by digging of rhizomes for horticultural and medicinal purposes. Western blue flag is an attractive plant and it is listed for sale in several gardening stores. Propagation can be done from either leed or rhizome although most gardening stores appear to be selling only seed. Western blue flag is included on the seed lists of some Alberta seed suppliers but it is difficult to track the source of these seeds. The impact of the removal of seed on the long term viability of populations is unknown. Various medicinal uses of Iris (including western blue flag) have been reported. These include induction of vomiting, cleansing the system and treating Staphylococcus sores. The rhizomes of western blue flag may also have anticancer properties. The full extent of collection of western blue flag in Alberta for horticultural or medicinal purposes is currently unknown. 

Pests and Diseases: No plant is immune from contracting diseases or pests. While no diseases have been reported in any of the known populations of western blue flag in Alberta., this does not mean that pests and diseases are not a threat. In fact, some researchers believe that western blue flag may be susceptible to fungus and other diseases when grown in cultivation. 

Herbicides:  Herbicides are used in various parts of the United States to control western blue flag. The chemical that is most effective in suppressing growth of this species is 2,4?D. It is used in areas in close proximity to western blue flag and is 91 to 100% effective in killing the plants. Some blue flag populations in Alberta, particularly at Hendry #4, are being adversely affected by the spraying of nearby willows.

Pollinators and Seed Dispersal Agents:  Pollination requires a minimum density of individuals and this may be a particularly important factor in small populations of western blue flag. The role of pollinators and seed dispersers in determining the status of western blue flag is unknown in Alberta. No information is available on whether bees are the active pollinating agents in his or if some other agent, such as other invertebrates or wind, is involved. Given that western blue flag is restricted to isolated patches in southern Alberta, and that flowering density may be quite small, the role of pollinators may be small but important. It may be that self-pollination is important in some of these populations. Detailed demographic and genetic studies of Alberta western blue flag populations are required to ascertain this.

Reprinted from Alberta Wildlife Status Report No. 21 (1999), with permission from Alberta Sustainable Resource Development.

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