Prairies Ecozone+ Evidence for Key Findings Summary
Theme: Habitat, Wildlife and Ecosystem Processes
- Agricultural landscapes as habitat
- Species of special economic, cultural, or ecological interest
- Primary productivity
- Natural disturbance
- Food webs
- Wildlife diseases and parasites
Agricultural landscapes as habitat
National key finding
The potential capacity of agricultural landscapes to support wildlife in Canada has declined over the past 20 years, largely due to the intensification of agriculture and the loss of natural and semi-natural land cover.
The agricultural landscapes of Canada include a variety of land cover types: native rangeland, tame pasture, summerfallow, and 24 types of cropland, as well as woodlots, wetlands, windbreaks, and other non-farmed areas.Footnote30 Footnote223 The agricultural landscape of the Prairie provinces increased from 35 to 55 million km2 between 1921 and the early 1970s. Javorek and Grant,Footnote84 in a more detailed analysis of recent trends for this report, found that the agricultural landscape expanded by 13,000 km2 between 1986 and 1996, then remained generally stable through to 2006. They found that close to 93% of the ecozone+ in 2006 was used for some form of agriculture (Figure 37). Approximately 55% of this was cropland, with the most common crops being wheat, cereal, oilseed, and pulses (chickpeas, dry beans, dry peas, and lentils). The area of land seeded to annual crops has increased steadily since 1921 (Figure 38) and cropland increased from 42% in 1971 to 55% in 2006.Footnote84
Source: Statistics Canada, 2007Footnote224
Long description for Figure 38
This line graph presents the following information (km2)
|Year||Total farmland||Land in crops|
Wildlife habitat capacity on agricultural land
The capacity of agricultural landscapes to provide habitat for wildlife depends upon the land cover type and management. Agricultural land in the Prairies Ecozone+ consists mainly of cultivated cropland with some extensive areas of tame pasture and native rangeland (Figure 39).Footnote84 With agriculture as the dominant land use, the population viability and persistence of many species depends upon the availability of suitable habitat on agricultural land. One way to measure the potential of these lands to support wildlife is through the Wildlife Habitat Capacity on Agricultural Land Indicator developed by Agriculture and Agri-Food Canada.Footnote84 Footnote225 The indicator ranks potential capacity of 15 “habitat categories” for terrestrial vertebrates based on the percent of the agricultural landscape occupied by 31 land cover types (e.g., cereal crops, summerfallow, tame hay, improved pasture, unimproved pasture, natural lands) and a rating of the value of each cover type as habitat to 588 species of birds, mammals, reptiles, and amphibians.Footnote84
Using the index, Javorek and GrantFootnote84 found that 340 species (245 birds, 71 mammals, 13 reptiles, 11 amphibians) could use agricultural land in the Prairies. Of these, 78% could use the All Other Land category (natural and semi-natural land including wetlands, riparian vegetation, and wooded areas within the agricultural landscape) for breeding and feeding, and 30% could use Unimproved Pasture (that is native rangeland) for both breeding and feeding. In contrast, only 4% were able to utilize cropland for breeding and feeding. However, when other suitable habitat was present to provide for partial life history requirements, 32% could use cropland. Godwin et al.Footnote128 showed the greatly reduced diversity in several taxonomic groups on cultivated land compared to even small remnants of native prairie.
The biggest change in land use has been the increase in area seeded to annual crops from 1971 to 2006, linked to the decrease in area of summerfallow (Figure 39). The total area of annually cultivated land, including both crops and summerfallow, declined from 66 to 62% of the agricultural landscape from 1986 to 2006, largely due to a shift of some cropland to seeded pasture (Figure 39).Footnote84 Cultivated land, offering comparatively little wildlife habitat, still represented the dominant portion of the agricultural landscape in 2006. Natural land for pasture (also known as unimproved pasture) was the second most abundant cover type and remained stable from 1971 to 2006 at about 25% of the agricultural landscape . The all other land category was also stable over that time period at about 5% of the landscape. The latter two cover types play a crucial role in determining the viability of wildlife populations in this ecozone+. It is the lower proportions of these cover types that are the primary reason for the overall low habitat capacity.
Source: Agriculture and Agri-Food Canada, 2009Footnote226
Long description for Figure 39
This line graph presents the following information:
|Year||crops||summerfallow||tame or seeded pasture||natural land for pasture||all other land|
In 1986, 1996, and 2006, the average wildlife habitat capacity was "low" or "very low" on over 80% of the farmland in the Prairies Ecozone+ (over 10% of this was ranked as "very low") (Figure 40). Despite slight shifts in the relative percentage among habitat capacity categories, there was no significant change in habitat capacity at the ecozone+ level.Footnote84 Wildlife habitat capacity was constant on 92% of farmland, increased on 5%, and decreased on 3%. However, conversion of small parcels, such as grasslands on field margins and small wetlands in the Prairies,Footnote24 can represent significant degradation of habitat capacity even when little change is detected at broader scales as was found hereFootnote84 (see Grasslands key finding on page 16 and Wetlands key finding on page 24 for discussion of loss of these habitats). Wildlife habitat capacity among ecoregions varied considerably; Moist Mixed Grassland Ecoregion had the lowest capacity and Cypress Upland Ecoregion had the highest, which was moderate capacity (Figure 40).Footnote84
Habitat capacity is a key indicator of an ecozone+'s ability to support biodiversity and can act as an umbrella indicator of how well overall ecological processes are functioning. Management practices also influence the ability of the land to support wildlife. The development of best management practices and stewardship initiatives has had positive results in some regions and for some cover types (see Stewardship key finding on page 36).
Soil erosion on cropland
Between 1981 and 2006, the proportion of croplandFootnoteiii with very low risk of erosion increased from 64 to 84%, and the amount of land with moderate to very high erosion risk decreased from 18 to 7% (Figure 41).Footnote227 The reasons for these decreases in erosion risk are a combination of widespread adoption of conservation tillage, especially zero-till seeding, and a marked reduction in summerfallow. Further, some of the more erodible land has been converted from annual crops to perennial forages and tame pasture with associated dramatic reductions in erosion risk.Footnote227 Many of these changes are beneficial for biodiversity.
Farmers have been working with conservation agencies to reduce the impact of tillage operations on soil erosion. Conservation tillage is the practice of minimizing plowing and retaining protective crop residues to reduce soil erosion Conservation tillage practices can also benefit waterfowl. The planting of winter wheat in the fall in a zero-till seeding practice eliminates the need for spring tillage thereby reducing disruption to nesting ducks. Application of these practices has increased since the early 1990s (Figure 42).Footnote110 Footnote228
Species of special economic, cultural, or ecological interest
National key finding
Many species of amphibians, fish, birds, and large mammals are of special economic, cultural, or ecological interest to Canadians. Some of these are declining in number and distribution, some are stable, and others are healthy or recovering.
Species at risk
As of 2014, 66 federally-listed species at risk were found in the Prairies Ecozone+: 25 listed as Endangered, 26 as Threatened, and 15 as Species of Special Concern.Footnote229The list is dominated by birds (20 species), plants (16 species) and insects (15 species) and many of these species are unique to the ecozone+. Most of them are found in small, localized areas, but a few are grassland endemics whose populations are steadily declining, although they are still relatively widespread at present. Many of the plants and several vertebrates are associated with open or sparsely vegetated sand environments (see Dunes key finding on page 34). Some are “peripheral” species, occurring at the edge of their range, while others may have a significant portion of their population in Canada but their numbers are declining, making them of global conservation concern.
Sprague's pipit (Anthus spragueii) is listed as Threatened under Canada's Species at Risk Act.Footnote230 It is a native grassland birdFootnote231 and could be considered an indicator of grassland health for the Prairies Ecozone+. It breeds strictly in North America's northern Great Plains, with most of the population in Canada. Sprague's pipit has declined steadily over the past 45 years (Figure 43).Footnote232 Habitat loss and habitat degradation (due to human disturbance, invasion by shrubs and non-native plants, and area and edge effects), and climate change are among the principal threats to Sprague's pipit.Footnote152
Source: Sauer et al., 2014Footnote232
Long description for Figure 43
This line graph shows the following information:
Greater sage-grouse (Centrocercus urophasianus) is an indigenous North American grouse species that occurs in Canada and eleven western U.S. states. Canada's population is the sub-species C. u. urophasianus, which occupies the silver sagebrush (Artemisia cana) grassland communities of southeastern Alberta and southwestern Saskatchewan, at the northern edge of the North American sage-grouse range.Footnote233 Greater sage-grouse is listed as Endangered under Canada's Species at Risk Act because the very small population has declined substantially.Footnote233 In 2012, based on counts of male birds at leks (areas used for courtship displays), the population was estimated at 39–58 adults in Alberta and 54–80 adults in Saskatchewan (Figure 44 ).Footnote233 Populations have declined by 98% since their highest recorded population estimates in Alberta (1968) and Saskatchewan (1988). The number of active leks has also decreased by 76% in Alberta and 93% in Saskatchewan. In 2012, there were only 5 active leks in Alberta and 3 in Saskatchewan.Footnote233
The main current and future threats to this species include drought and extreme weather conditions, West Nile virus, sensory disturbance from vertical structures and chronic noise, increased predator pressure, habitat loss and degradation, alteration of natural hydrology, and threats inherent to small populations.Footnote233
Source: Environment Canada, 2013Footnote233
Long description for Figure 44
This line graph presents the following information:
In 2013, the Government of Canada published an Emergency Order to protect the greater sage-grouse on crown lands in southeastern Alberta and southwestern Saskatchewan.Footnote234 The Order, which came into force on February 18, 2014, prohibits activities that are known to be harmful to the birds and their habitat. In addition to the Order, private landowners are being encouraged to undertake voluntary stewardship measures and a captive breeding program has been initiated in partnership with the Calgary Zoo.
Burrowing owl (Athene cunicularia; EndangeredFootnote230) is found across the Prairies Ecozone+ where it represents the northern limit of the species' range. Its population in Canada declined strongly from the 1960s to 2007 (Figure 45). The Canadian population of burrowing owl in 2004 was estimated at 498 birds in Saskatchewan, and 288 in Alberta, but this estimate might be low by as much as 50%.Footnote235 A variety of causes for this decline have been suggested: loss of grassland habitat (the initial cause of the decline), greater emigration than immigration of birds from Canada to the U.S., loss of burrows from declining burrowing animal populations, increased predation resulting from habitat changes, reduction in invertebrate food sources through the use of chemical pesticides, and vehicle collisions.Footnote235
The swift fox (Vulpes velox; ThreatenedFootnote230) is an example of a conservation success story. Originally occurring across the Prairies from Manitoba's Pembina Hills to the foothills of the Rocky Mountains in Alberta, it was extirpated from Canada by the late 1930s.Footnote237 Attempts to reintroduce it started in 1983. CarbynFootnote238 documented the release of 768 foxes from 1987 to 1995 and in 1996/1997, the Canadian population was estimated at 281 animals, of which 17% had been released and the rest were wild-born animals.Footnote239 By 2005/2006, the population had increased to an estimated 647 animals, with an additional 500 animals thought to be established in the adjacent region of Montana as a result of the Canadian reintroduction program. Although a success story so far, the population currently occupies only a small proportion of its original range, amounting to less than 300 km along the Canada-U.S. border in Alberta and Saskatchewan.
Based on data from the American Fisheries Society,Footnote240 the number of freshwater and diadromous fish taxa in this ecozone+ classified as imperilled has increased from two in 1979 to five in 2008. However, the assessment for lake sturgeon (Acipenser fulvescens) and shortjaw cisco (Coregonus zenithicus) improved between 1989 and 2008; they were downlisted to Vulnerable and Threatened, respectively.
Large ungulate populations have shown varying patterns of abundance and distribution, with some species increasing and others decreasing. Hunting is now regulated to prevent overharvesting, but populations continue to vary with weather fluctuations and habitat change.
The pronghorn (Antilocapra americana) is a small-sized, fast-moving ungulate with two-pointed horns that is native to interior western and central North America.Footnote241 Historically found from Manitoba's Red River to the edge of the Rocky Mountains in Alberta,Footnote242 numbers were thought to equal or exceed those of bison on the Great Plains prior to European settlement. Conversion of grassland to cropland reduced pronghorn distribution to peripheral ranges, which historically supported low-density populations.Footnote243 Pronghorn numbers at the northern end of their range in Canada have always fluctuated widely because of mass emigration across the border or high winter mortalityFootnote244and were lowest at the beginning of the 20th century (Figure 46). They have recovered somewhat since then, although their range is still restricted. SheriffFootnote241 found that pronghorn abundance was strongly positively associated with native prairie. They are also highly dependent on sagebrush communities. The largest populations coincide with large expanses of remaining natural habitat. Threats include loss of movement corridors, barriers such as fences, and roads that can increase mortality risk.Footnote243
Long description for Figure 46
This line graph presents pronghorn population trends in Alberta and Saskatchewan between 1900 and 2008. Population numbers prior to 1945 represent archive guesses while post-1945 numbers are based on systematic surveys. The line graph for Alberta shows the following information:
In Saskatchewan, populations began at approximately 25,000 in 1900, and then dropped to a very small number in the 1920s. From the mid-1920s to 1950, the population increased after which it fluctuated but remained steady until 1975. After 1975, the population increased rapidly to just over 30,000 in 1990, before declining to approximately 15,000 in 2008.
Abundant in the Prairies prior to settlement, elk (Cervus elaphus) became largely restricted to pockets of forestFootnote245 but, since the 1990s, have begun to rapidly re-occupy non-forest habitats.Footnote108 Footnote164 Footnote217 Footnote246 Footnote247
Moose (Alces alces), which typically occur in the Boreal Forest, have increased and extended their range into the Prairies since the late 1970s to mid-1980s.Footnote164 Footnote217 Footnote246 This expansion was likely a result of a reduction in hunter numbers, reduction or elimination of predators such as wolves and bears, and increasing amounts of woody vegetation.
Mule deer (Odocoileus hemionus) were the more common deer in the Prairies prior to European settlement, but are currently less abundant, being more restricted to open habitats with rougher topography.Footnote248 Footnote249 White-tailed deer (O. virginianus)may have been largely absent from the Prairies Ecozone+ before European settlement.Footnote245 Footnote248 They are very common, especially in the Aspen Parkland Ecoregion. Populations expanded rapidly in the 1940s and 1950s and have generally continued to expand.Footnote250 Footnote251 Footnote252 Because the Prairies Ecozone+ is near the north end of the white-tailed deer's range, winter weather is the main factor limiting current populations, with fluctuations closely linked to severe winters.Footnote252 The main reasons for expansion over the last 50 years have been reduced competition with mule deer, high quality and abundance of food provided by agriculture, and expansion of aspen.Footnote250 Footnote251 Footnote252 Footnote253
The Prairies Ecozone+ includes more grassland than any other ecozone+ and is the heart of range of many grassland birds in Canada. Grassland birds declined more rapidly than any other group of birds in North America since the 1970s,Footnote50 Footnote254 Footnote255 and this is reflected in the results for the Prairies Ecozone+ (Figure 47) (see the Grasslands key finding on page 16).
In contrast, forest birds in the Prairies Ecozone+ increased by 35% in overall abundance since the 1970s (Figure 47). This assemblage benefitted from increased forest habitat as a result of tree planting on farms and in other settlements as well as the increased tree cover in areas of Aspen Parkland Ecoregion (see Forests key finding on page 15).Footnote17, Footnote256 Birds of other open and shrub/early successional habitats were relatively stable and urban/suburban birds decreased as a group (Figure 47). Birds of forest, urban, and shrub/early successional habitats are a relatively small component of prairie avifauna.Footnote49
Long description for Figure 47
This bar graph presents the following information:
|Species Assemblage||Percentage of change from 1970 index|
|Other / Open||-8%|
Because of their position high in the food web, raptors are indicators of ecosystem health. Data from the Breeding Bird Survey was analyzed to look at trends in raptor populations in the Prairies Ecozone+. Of the four species showing statistically significant trends, three were positive, while one, short-eared owl (Asio flammeus), was negative (Figure 48). Red-tailed hawk (Buteo jamaicensis) has increased 3.3%/yr, and it has replaced Swainson's hawk (Buteo swainsoni) as the dominant Buteo and most abundant raptor in the ecozone+.257 This is probably due to the gradual expansion of tree cover.Footnote258 Footnote259
The waterfowl found in the Prairies Ecozone+ are diverse, with a variety of different habitat requirements and migratory strategies. Some species winter on Canadian coasts while the majority winter in the U.S. and Mexico.Footnote58 The Prairie Pothole Region (U.S. and Canada) is the world's most productive waterfowl habitatFootnote62 and, although it only covers 10% of the available breeding habitat in North America, it supports the highest densities of breeding waterfowl and can account for greater than 50% of annual continental duck production.Footnote58 Footnote59 The Canadian Prairies produce 50–80% of the Prairie Pothole Region's duck population.Footnote261 The Prairies Ecozone+ is also an important area for migrating waterfowl. Many ducks and geese that nest in the Arctic, sub-Arctic, and boreal forest pass through this area during migration, stopping in staging areas.
Some waterfowl species are showing long-term population increases. For example, Canada geese populations have increased by 765% since the 1970s due to their ability to adapt to a variety of habitats including farmland and urban areas.Footnote219 Footnote262 Some species have declined significantly, such as northern pintail (Anas acuta) and American wigeon (A. americana). Other species, such as blue-winged teal (A. discors) and canvasback (Aythya valisineria), have shown little long-term change in their population size since the 1970s (Table 6).
|Common name||Nesting habitat||Trend (%/yr)||P||Annual abundance index (in 1000s)|
|Annual abundance index (in 1000s)|
|Annual abundance index (in 1000s)|
|Annual abundance index (in 1000s)|
P is the statistical significance: * indicates P <0.05; n indicates 0.05<P<0.1; no value indicates not significant
Source: Fast et al., 2011Footnote219, using data from CWS and USFWS Waterfowl Breeding Population and Habitat SurveyFootnote59
Increased conversion of marginal land to cropland over the last four decades (see Agricultural landscapes as habitat key finding on page 64) has likely had continuing negative impacts on many breeding waterfowl on the Prairies through habitat loss and changes in predation patterns. For example, nest success for mallard (Anas platyrhynchos), northern pintail, northern shoveler (A. clypeata), blue-winged teal, and gadwall (A. strepera) is negatively associated with proportion of cropland.Footnote263
Climatic conditions, such as drought in the 1980s, also had a large impact on waterfowl populations; many populations steadily increased after the drought (Table 6). Wetland abundance and distribution affects several prairie breeding ducks (see Wetlands key finding on page 24).Footnote263 Footnote264 Footnote265 Footnote266 Footnote267 Footnote268 Footnote269 Northern pintail, blue-winged teal, mallard, and northern shoveler breeding densities fluctuate with numbers of prairie ponds suggesting that these species fly over the prairies in drought years and settle in more northern ecozones+.Footnote268 These species, along with green-winged teal (Anas crecca), are dabbling ducks that are typically associated with shallow temporary and seasonal wetlands (i.e., ephemeral habitats). Consequently, some of these species may be more sensitive to fluctuating water conditions (which influences wetland densities) and wetland destruction than other species such as gadwall and diving ducks (e.g., canvasback, ruddy ducks), which are more associated with semi-permanent and permanent wetlands that are less susceptible to drought conditions and drainage.Footnote268 As such, duck species that use small wetlands prone to agricultural modification or destruction and climate fluctuations are generally the species that are declining (Table 6).
Long description for Figure 49
This line graph presents the following information:
|Year||American Wigeon||Blue-winged Teal||Gadwall||Green-winged Teal||Mallard||Northern Pintail||Northern Shoveler|
Case study: northern pintail
Unlike most other waterfowl species, the northern pintail population in North America has remained well below the North American Waterfowl Management Plan goal of 5.6 million birds. In 2007, the population was 40% below the plan's goal and 19% below the long-term average (Figure 50).Footnote270 Typically, the number of pintails that settled on the Prairie Pothole Region had a consistent and positive relationship with numbers of wetlands counted during May surveys. Since the early 1980s, however, the strength of this relationship had weakenedFootnote271 and there was no relationship between pintails and wetlands in the mid-1990s when water conditions were excellent. Comparison of population trends between the Canadian and U.S. portions of the Prairie Pothole Region indicate that most of the decline occurred in the southern Canadian portion of the region. A primary cause for the decline is the tendency of northern pintail to nest in standing stubble, mulched stubble, or fallow fields early in the season often prior to seeding. The reduction of summerfallow and increase of spring seeding since the 1970sFootnote84 has been linked to reduced nest success and a decline in the northern pintail population in the Canadian portion of the region.Footnote272 Footnote273
Long description for Figure 50
This line graph presents the following information:
|Year||Alaska and |
|Northern U.S.||Southern Canada|
The Prairies Ecozone+ provides important habitat for both breeding and migrant shorebirds. This includes eight species whose breeding range in Canada is primarily or entirely in the Prairies: American avocet (Recurvirostra americana), marbled godwit (Limosa fedoa), piping plover (Charadrius melodus), Wilson's phalarope (Phalaropus lobatus), black-necked stilt (Himantopus mexicanus), willet (Tringa semipalmata), long-billed curlew (Numenius americanus) and upland sandpiper (Bartramia longicauda). Data for these species was limited to the Breeding Bird Survey. Population totals of shorebird species tend to number in the tens to hundreds of thousands, with a few in the millions.Footnote274 The only species with a significant trend was marbled godwit, which declined by 1.1% per year since the 1970s.Footnote275 This is important as approximately 60% of the world's population breeds in the Canadian Prairies.Footnote276 There is little information on population trends for the 31 species of shorebirds that regularly migrate through the Prairies in the spring and fall.Footnote277 Footnote278 Footnote279
Major range shiftshave occurred in a number of native species including white-tailed deer (see Deer on page 75), moose (see Moose on page 75), red-tailed hawk (see Raptors on page 76), and raccoon (Procyon lotor).280 LarivièreFootnote280 documented the increase in raccoons in the Prairie provinces by examining fur sale records for each of the provinces. Sales of raccoon pelts in Manitoba climbed from near zero in 1960 to almost 1,000 in 1969, peaking at over 7,000 in the early 1970s. The increase in Saskatchewan occurred slightly later, starting in 1970, and numbers in Alberta showed little fluctuation above a low baseline through to 1985.
Climate change will also enable more warm water fish species to expand their ranges. The channel catfish (Ictalurus punctatus) is a native species that has increased its range, moving up the Qu'appelle River from Manitoba into Saskatchewan.Footnote114 Rainbow smelt (Osmerus mordax), an anadromous species of North America's east and west coasts, has appeared in Manitoba with the first report occurring in Lake Winnipeg in 1975. White bass (Morone chrysops), introduced to North Dakota in 1953, appeared in Lake Winnipeg 10 years later and by 1994 had become the most abundant spiny-rayed fish in the Lake's south basin.Footnote157
National key finding
Primary productivity has increased on more than 20% of the vegetated land area of Canada over the past 20 years, as well as in some freshwater systems. The magnitude and timing of primary productivity are changing throughout the marine system.
The Normalized Difference Vegetation Index (NDVI), calculated from remote sensing data, is an indicator of the amount and vigour of green vegetation present on a landscape. Changes in NDVI are a proxy for changes in primary productivity. Trends in annual peak NDVI values over a 22-year period (1985–2006) were analyzed by Pouliot et al.Footnote281 The significant results were then summarized by ecozone+ and visually compared to 1995 land cover (derived from Advanced Very High Resolution Radiometer data by the Canadian Centre for Remote SensingFootnote282) by Ahern et al. (2011).Footnote7 Results show that, between 1985 and 2006, NDVI values increased for 157,491 km2 (35.1%) of the Prairies Ecozone+ and decreased for 1,116 km2 (0.2%) (Figure 51). Increases were distributed widely while decreases in NDVI were confined to a small area in southeastern Alberta. Broad increases in NDVI in this ecozone+ have also been shown by Slayback et al.,Footnote283 Zhou et al.,Footnote284 and Tateishi and Ebata.Footnote285
National key finding
The dynamics of natural disturbance regimes, such as fire and native insect outbreaks, are changing and this is reshaping the landscape. The direction and degree of change vary.
The main natural disturbance regimes that have historically shaped the Prairies include fire, drought, bison grazing, and large-scale native insect outbreaks.
Under pre-European settlement conditions, frequent fires were the predominant disturbance regime of grasslands in the Prairies Ecozone+. In addition to natural fires caused by lightning,Footnote286 some burning was anthropogenic.Footnote205 Footnote287 Footnote288 Footnote289 There is no way to measure historic fire frequency, but 5–10 years is a “reasonable” estimate of the natural fire-return interval.16 Under modern conditions, prairie fires still start under dry conditions,Footnote16 sometimes ignited by lightning.Footnote290 They do not travel as far as they did historically, however, as a network of firebreaks in the form of roads and cultivated fields break up the grassland,Footnote16 and accidental grass fires are aggressively suppressed to reduce damage to forage and facilities. No quantitative data were available for the extent or frequency of fires across the ecozone+.
In a review of threats to native areas in the Northern Great Plains of the U.S. and Canada, the Nature ConservancyFootnote291 rated “loss of fire regime” as the second-most serious threat to this region. Fire is a natural and essential process which, like grazing, creates and maintains variety in the prairie landscape. In tallgrass prairie, however, Collins and SmithFootnote292 found that frequently repeated burns reduce spatial variability and diversity, increasing the dominance of a few C4 grass species. In the mixed prairie, which covers most of this ecozone+, productivity is probably higher now than before European settlement, because fire causes a reduction in productivity that lasts for three years or more.Footnote16 Footnote17 Footnote293 Footnote294 Footnote295 In moister parts of the ecozone+, the reduction in fire frequency has led to increases in shrub and tree cover, because frequent fire tends to suppress woody plants and favour grasses.Footnote12 Footnote13 Footnote16 Footnote17 In some areas, woody invasion threatens native grassland communities, such as the northern fescue prairie. Fire suppression may also contribute to sand dune stabilization, reducing habitat for certain rare species associated with active dunes.Footnote99 PylypecFootnote296 found that some birds such as horned lark increase after grassland fire, while others such as Sprague’s pipit, Baird’s sparrow (Ammodramus bairdii), and western meadowlark (Sturnella neglecta) decrease after fire.
Large-scale native insect outbreaks
Insect herbivores are an integral part of prairie ecosystems, with outbreaks of some native species functioning as disturbance agents. Grasshoppers (order Orthoptera) are the most significant insect pests to grasslands and cereal crops in many parts of the Prairies.Footnote297 Their populations increase when late summers are dry and warm,Footnote298 Footnote299 and major grasshopper outbreaks occur after several consecutive years of warm, dry weather.Footnote297 No data were available on trends in the pattern of grasshopper outbreaks.
Forest tent caterpillars (Malacosoma disstria) and other insects can significantly defoliate trembling aspen in the Aspen Parkland Ecoregion in some years,Footnote300 and like the grasshoppers, outbreaks occur more frequently in warm, dry summers.Footnote301 Outbreaks were much more frequent and severe in the Aspen Parkland in the 1980s and 1990s than in the 1940s to 1970s. They peaked in the early 1980s before severity declined in the early part of the 2000s (Figure 52).Footnote302
Source: Canadian Forest Service, unpublished dataFootnote302
Long description for Figure 52
This line graph presents the following information:
|-||% White tree-rings||% Area defoliated|
Another insect disturbance agent of the Prairies Ecozone+ is the mountain pine beetle (Dendroctonus ponderosae), which is native to the unique lodgepole pine (Pinus contorta) forests of Cypress Hills. A significant outbreak occurred in the 1980sFootnote303 and the population was beginning to increase again in 2008.Footnote304
National key finding
Fundamental changes in relationships among species have been observed in marine, freshwater, and terrestrial environments. The loss or reduction of important components of food webs has greatly altered some ecosystems.
Changes to the food webs and trophic dynamics in the Prairies Ecozone+ have included changes in herbivore grazing patterns and intensity due to the replacement of bison herds with domestic livestock and the loss of large predators.
As discussed in the Grasslands key finding on page 16, the historic impacts of free-roaming bison on grasslands were thought to be very different from the impacts of confined bison herds and domestic beef cattle today. Although the relationships among grazing, grassland biodiversity, and invasive non-native plants are complex, the presence of a wide range of grazing intensities appears better for maintaining prairie biodiversity than uniform grazing management.Footnote44 Footnote45 In some areas, grazing regimes more similar to historic patterns have been implemented for conservation purposes (e.g., Grasslands National Park).Footnote305
Large predators, such as the grey wolf (Canis lupus) and grizzly bear (Ursus arctos), have been eliminated or substantially reduced as a result of European settlement (Figure 53).Footnote306 The decline of the grey wolf began with the extirpation of the plains bison in the late 1800s and continued due to over-hunting of ungulate prey and predator control.Footnote307 Across North America, the loss of the wolf has, among other impacts, resulted in increased abundances of ungulates, leading to increased browsing on vegetation.Footnote308 Although hunting has played a role similar to ungulate predation, it can also be selective based on age, sex, or other characteristics, leading to demographic effects on the overall population and decreased fecundity,Footnote309 or unintentional evolutionary consequences (e.g., selection for small antler size).Footnote310 However, studies showing these effects have not been carried out in the ecozone+.
Because wolves tend to dominate other carnivores,307 the loss of wolves has probably contributed to increased coyote (Canis latrans) populations.Footnote311 In southeastern Alberta, coyote abundance increased 135% between 1977–1989 and 1995–1996.Footnote311 Coyotes eat a wide variety of foods including rodents, rabbits, woodchucks, songbirds, fruits, and domestic livestock (especially sheep). Although they do prey upon wild ungulates, much of the ungulate meat coyotes consume is from carrion.Footnote312 The shift in top predators from wolves, that mainly hunted ungulates, to coyotes, shifted the abundance and distribution of prey species. Coyotes are also a major predator of duck nests.Footnote313 Coyotes, along with golden eagles (Aquila chrysaetos), are also the main predators of the reintroduced swift fox.Footnote311 Footnote314 Footnote315 Footnote316
Wildlife diseases and parasites
National key finding
Wildlife diseases and parasites was initially identified as a nationally recurring key finding and information was subsequently compiled and assessed for the Prairies Ecozone+. In the final version of the national report,Footnote3 information related to wildlife diseases and parasites was incorporated into other key findings. This information is maintained as a separate key finding for the Prairies Ecozone+.
A wide variety of diseases affect wildlife in the Prairies Ecozone+:Footnote317
- Avian influenza in wild ducks;
- Botulism in waterfowl;
- Avian cholera in migrating geese;
- Newcastle disease virus in double-crested cormorants (Phalocrocorax auritus);
- Ranavirus in amphibians;
- Chytrid fungus in amphibians;
- Epizootic hemorrahic disease and Bluetongue virus in deer and pronghorns;
- Chronic wasting disease in deer and elk;
- Brainworm (Parelaphostrongylus tenuis) in deer, elk, and moose;
- Winter tick in moose;
- Tuberculosis in elk;
- Lyme disease in deer;
- Morbillivirus in carnivores such as the reintroduced swift fox and black-footed ferret (Mustela nigripes); and
- Plague bacterium in colonial ground squirrels and prairie dogs, which could also spread to black-footed ferret.
One disease (chronic wasting disease) and one parasite (botulism) are described in more detail below as examples of the known and potential impacts on native wildlife populations, along with an example of a disease impacting tree populations (Dutch elm disease).
Chronic wasting disease
Chronic wasting disease (CWD) is a fatal disease to members of the deer family (cervids; family Cervidae) resulting from ingestion of a misfolded version of a normal body protein called the prion protein.Footnote318 Footnote319 CWD was first recognized as a clinical disease in 1967 in mule deer housed at a research station in Colorado.Footnote319 The disease has spread widely in the U.S. and Canada (Figure 54), often in association with the sale and transport of farmed cervids. CWD was first reported in Canada in 1996 in captive elk on game farms in Saskatchewan.Footnote320 In 2000 it was detected in a wild mule deer and has since been detected in four separate geographical areas of the Prairies Ecozone+ in mule deer, white-tailed deer, and elk. CWD is a serious ecological and economic concern to Canada. The approximately 1.8 million white-tailed deer, 350,000 mule deer, 100,000 elk, and 900,000 moose in Canada are susceptible to CWD and there are no natural barriers to prevent its spread from its current locations to the rest of the country.Footnote321 A CWD disease control and eradication policy was implemented by the Canadian Food Inspection Agency (CFIA) in October 2000. Testing is mandatory in Manitoba, Saskatchewan, Alberta and the Yukon. Where captive animals have tested positive, exposed herds have usually been destroyed to minimize the risk of spread.Footnote322
Botulism is a form of food poisoning associated with the ingestion of powerful toxins produced by various strains of the bacterium Clostridium botulinum. Although it has occurred in other ecozones+, type-C botulism has caused large and recurrent epidemics only in the Prairies Ecozone+, affecting waterfowl, especially ducks. The alkaline wetlands of the Prairies Ecozone+ are habitats favourable to type-C botulism. In the mid-1990s, repeated years of high mortality occurred in southern Alberta, Saskatchewan, and Manitoba. For example, over 100,000 ducks died in late fall at Old Wives' Lake in southern Saskatchewan in 1996, and total mortality from June to October was approximately one million birds.Footnote324 Footnote325 These outbreaks were associated with summer drought conditions during which many of the small wetlands used by waterfowl for nesting were dry and large numbers of birds were concentrated on a small number of large wetlands where suitable habitat remained available. There was a marked reduction in mortality from botulism in subsequent years when precipitation relieved drought conditions.Footnote325
Dutch elm disease
Dutch elm disease is a fungal disease of elm trees. Since its introduction to Canada in Quebec in about 1940, it has spread quickly, invading Ontario by 1946, the Maritimes by 1957, Manitoba by 1975, and Saskatchewan by 1981.Footnote326 Control measures have generally focused on urban areas and as a result, wild trees have suffered high mortality rates. In Saskatchewan, mortality rates exceeded 80%.Footnote327 In Winnipeg, 40,000 city elms were lost over the past 20 years, with 200,000 remaining.Footnote328 Isolated pockets of wild trees occur as far west as Saskatoon and Assiniboia and these are probably the only natural populations in Canada that remain uninfected.Footnote327
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