Taiga Plains Ecozone+ Evidence for Key Findings Summary
- List of Figures
- List of Tables
- Ecozone+ Basics
- Key Findings at a Glance: National and Ecozone+ Level
- Theme: Biomes
- Theme: Human/Ecosystem Interactions
- Theme: Habitat, Wildlife, and Ecosystem Processes
- Theme: Science/Policy Interface
- Conclusion: Human Well-Being and Biodiversity
Theme: Habitat, Wildlife, and Ecosystem Processes
- Species of special economic, cultural, or ecological interest
- Primary productivity
- Natural disturbances
- Wildlife disease and parasites
- Food webs
Key finding 17
Species of special economic, cultural, or ecological interest
Theme Habitat, wildlife, and ecosystem processes
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.
Ecozone+ key finding: The Taiga Plains Ecozone+ is important nationally for boreal woodland caribou, who are dependent upon intact blocks of mature boreal forest. Trends are unknown for half of the populations in the Taiga Plains Ecozone+; populations in the more fragmented, southern part of the ecozone+ are decreasing, although one population is reported as being stable. Bluenose-West barren-ground caribou have declined precipitously in recent years. Several waterfowl species that breed in the ecozone+ are declining; causes are not clear. The Taiga Plains is home to most of the global populations of two iconic species that were nearly driven to extinction in the early 20th century and are still considered at risk: the whooping crane and the wood bison.
This section presents accounts of status, trends, and conservation issues for selected species in the Taiga Plains Ecozone+. Two iconic species that had been driven close to extinction by human settlement and exploitation, the wood bison and the whooping crane, have seen population increases due in large part to conservation measures taken in the ecozone+, but restricted ranges and other concerns mean that ongoing efforts are required to maintain healthy, viable populations. The Taiga Plains Ecozone+ provides important habitat for caribou and grizzly bears, species valued by humans living within and outside of the ecozone+, and, with its numerous boreal forest wetlands, is important both as breeding habitat and as staging habitat during migration for waterfowl.
In the accounts below, COSEWIC refers to the Committee on the Status of Endangered Wildlife in Canada, a committee of experts that assesses wildlife species and designates which are in danger of disappearing from Canada. SARA refers to the Species at Risk Act.
The conservation ranking for wood bison (Bison bison athabascae) has improved due to intense efforts to re-build populations. COSEWIC initially assessed wood bison as Endangered in 1978, then down-listed the species to Threatened in 1988. This status was reaffirmed in 2000. Wood bison are protected under the Species at Risk Act.Reference 157
During historic times, wood bison, Canada’s largest terrestrial mammal and a northern subspecies of the American bison, ranged over most of the boreal region of North America west of the Precambrian Shield. Historical estimates are reported as about 150,000Reference 157 or over 168,000.Reference 158 Abundance declined in the 19th century due to the invention and spread of firearms and the consequent overharvest of wood bison.Reference 159 The population was about 300 animals in 1893, confined to a small area in the southeastern Taiga Plains, when the first protective legislation was enacted to control hunting.Reference 160 Wood bison numbers reached an all-time low of about 250 animals in 1896.Reference 158 The remaining habitat was protected as Wood Buffalo National Park in 1922. A national recovery program was established in 1957. Eighty to ninety percent of the total wood bison population is in the Taiga Plains Ecozone+ and the adjacent section of Wood Buffalo National Park (Table 6).
Disease (brucellosis and tuberculosis, as well as outbreaks of anthrax – see also key finding on Wildlife diseases on page 79), cross-breeding with plains bison, and habitat loss through development (agriculture, forestry, and oil and gas) are the main threats faced by wood bison.Reference 157 From 1925 to 1928, 6,673 plains bison were shipped from Buffalo National Park, near Wainwright, Alberta, to Wood Buffalo National Park. These plains bison were from a herd that was being culled due to infection with tuberculosis, but the young animals introduced to Wood Buffalo National Park were thought to be disease-free. The relocated plains bison hybridized with the endemic wood bison and introduced tuberculosis to the herd. The source of brucellosis is less clear.Reference 161
Conservation efforts include measures to keep disease-free populations from making contact with diseased animals. The NWT’s Bison Control Area (Figure 31), established in 1987, is surveyed annually and kept free of bison to protect the Mackenzie herd from disease.Reference 162 In 2011 and 2012 infected bison have spread to the west of Wood Buffalo National Park, leading to intensified management efforts in this part of Alberta. The aim is to keep the disease-free Hay-Zama herd from contact with diseased animals and to control the risk of tuberculosis and brucellosis spreading to cattle.Reference 163 Maintaining bison-free zones has a cost in terms of habitat loss. About 50% of the historical range of wood bison is unavailable for recovery because of the need to control the spread of wildlife disease.Reference 164 Ranges of wood bison populations in or near the Taiga Plains Ecozone+ are shown on Figure 31 and status and trends are outlined in Table 6.
|Population||Status and trends|
|Wood Buffalo National Park||The total population was about 12,000 in the 1960s, declining to 2,100 in 1999. In 1974/75, 3,000 bison perished due to flooding in the Peace-Athabasca Delta. The population has increased in recent years and was estimated at 5,000 in 2009.Reference 160, Reference 166 The herd expanded to the west in 2011 and 2012.Reference 163 |
Infected with bovine tuberculosis and brucellosis (introduced through importation of infected plains bison in the late 1920s)Reference 160 and subject to several severe anthrax outbreaks since 1962.Reference 167
|Slave River Lowlands||Considered part of the Wood Buffalo National Park population. Also infected with bovine tuberculosis and brucellosisReference 162 and subject to anthrax outbreaks.Reference 167|
Declined from between 1,300 and 2,500 bison in the 1960s to about 500 by the 1980s, remaining stable for the next 20 years, then increasing to about 1,700 by the year 2009.Reference 162, Reference 166
|Nahanni||Established 1980 with release of 28 bison.Reference 162|
Between 1989 and 1998, 71 more bison were released and, by March 2004, there were an estimated 400 bison.Reference 162 A survey in 2011 showed that the population numbers have remained stable at about 400.Reference 166
|Hay-Zama Lakes||Established 1984 with introduction of 29 bison; population grew to about 500 by 2007.Reference 39 A 2012 survey counted 587 bison, within the management goal of 400 to 600.Reference 163 |
Permit hunt started in 2008, in part to keep the herd from expanding and coming in contact with infected animals from the Wood Buffalo National Park population.Reference 168 All animals tested through the harvest have been determined to be disease-free.Reference 163
|Mackenzie||The largest healthy herd in northern Canada.Reference 162, Reference 166 |
Established 1963 by releasing 18 bison near Fort Providence. The herd expanded its territory and increased to 2,400 animals by 1989, followed by a decline to 1,600 bison in 2008. An anthrax outbreak in August, 2012 killed 440 bison, reducing the herd to fewer than 1,000 animals.Reference 166
Sources of mortality include anthrax outbreaks in 1993Reference 169 and 2012Reference 166 and loss of bison through thin spring ice in 1989.Reference 162
COSEWIC designated the whooping crane (Grus Americana) as Endangered in Canada in 1978 and the species is protected under SARA.Reference 170 The whooping crane, never a common species, was reduced to an estimated 1,400 birds in 1860, with most of these remaining birds disappearing over the next 40 years due to encroachment of settlement on all but the northernmost of its breeding grounds. Wintering habitat also contracted during this time. The all-time low for the population was 14 known adults.Reference 171 The breeding range, which had extended across much of the central and northern prairies of North America, was reduced to a single site in Wood Buffalo National Park.
The only remaining self-sustaining wild population in the world breeds in Wood Buffalo National Park within the Taiga Plains Ecozone+ and migrates to the Aransas National Wildlife Refuge along the Gulf of Mexico, in Texas.Reference 171 Two additional non-self-sustaining populations have been established in the United States. One, with reintroduction starting in 2001, migrates between the Wisconsin and Florida.
The Canadian whooping crane wild population has increased from 18 in 1938 to 283 in the winter of 2010/11.Reference 172 Current threats include limited genetic diversity of the species and loss and degradation of migration stopover habitat and coastal wintering habitat, as well as threat of chemical spills in Texas.Reference 173
Whooping cranes breed in isolated wetlands with soft substrates, substantial amounts of open water (creating long sight lines for spotting predators), and suitable vegetation for nesting materials. They have, over the years, expanded their breeding range locally, and it is considered that there is ample suitable habitat in the vicinity of their current range in the Taiga Plains Ecozone+.Reference 171 Population growth is likely to be controlled more by limitation of suitable habitat on the wintering grounds in TexasReference 171, Reference 173 Predation on the breeding range may, however, influence the rate of population growth. The 10-year cycle for predators, especially wolves, in Wood Buffalo National Park was considered by Boyce and Miller, 1985Reference 174 to account for the slight periodicity in population abundance, with slowed growth and slight dips approximately every 10 years (Figure 32). A national recovery strategyReference 175 and an international recovery planReference 173 are in place to coordinate monitoring, research, and conservation measures for the whooping crane.
Total population, based on winter counts.
Source: based on data from COSEWIC, 2010;Reference 171 2010 and 2011 data from Whooping Crane Conservation Society, 2011Reference 172
Long description for Figure 32
This line graph shows the following information:
|Year||Total counts||Year||Total counts|
Migratory barren-ground caribou (Rangifer tarandus groenlandicus) winter in the Taiga Plains Ecozone+ and non-migratory woodland caribou (Rangifer tarandus caribou) range through much of the ecozone+ year-round.
This section, based on the report on Northern caribou population trends in Canada,Reference 97 a technical thematic report prepared for the 2010 Ecosystem Status and Trends Report, presents population trend information for the two barren-ground caribou herds: the Bluenose-East and the Bluenose-West. Both herds calve in the Southern Arctic (Arctic Ecozone+) and winter in the Southern Arctic and the Taiga Plains ecozones+.
The Bluenose-East Herd was not officially recognized as a distinct herd until 1999.Reference 176 A photographic post-calving survey was undertaken in 2000, providing an estimate of 104,000 ± 22,100 (95% CI) (Figure 33). This was followed by a decline to an estimated 70,100 ± 8,100 in 2005 and 66,800 ± 5,200 in 2006. This translates into a 10% exponential rate of decline from 2000 to 2006. However, by 2010, the post-calving herd estimate was 98,600 caribou ± 7,100. There are gaps in the information as demographic rates were not monitored and information on distribution based on collared caribou has not been analyzed.
Estimates are for caribou one year and older. Surveys were conducted in July.
Source: Gunn et al., 2011Reference 97
Long description for Figure 33
This bar graph presents the following information:
|Population estimate, post-calving photo survey||104,000||70,081||66,754||98,646|
|95% confidence intervals||22,100||8,120||5,182||7,125|
Trends in vital rates are uncertain as monitoring has been infrequent until recently. Spring calf:cow ratios ranged between 25 and 52 calves: 100 cows and showed no trend between 2001 and 2009 (R. Popko, unpublished data in Adamczewski et al., 2009).Reference 177
Although the Bluenose-West Herd was not officially recognized as a distinct herd until 1999,Reference 176 population estimates were derived for 1986, 1987, and 1992 based on locations of radio-collars during post-calving surveys of the Bluenose Herd. The herd peaked at 112,400 ± 25,600 (95% CI) in 1992 and then declined to 76,400 ± 14,300 in 2000, and 20,800 ± 2,040 in 2005 (Figure 34). The 2005 estimate was confirmed by an estimate of 18,050 ± 530 caribou in 2006. Since then, the trend appears to have leveled out, with a preliminary estimate for a July 2009 survey of 17,900 ± 1,300 caribou.Reference 178
Population estimates are for caribou one year and older. Data obtained during phot°Census surveys of the “Bluenose” herd prior to 2000 were re-analyzed to estimate Bluenose-West population trends. These estimates should not be considered as reliable as the later estimates.Reference 179
Source: Gunn et al., 2011Reference 97
Long description for Figure 34
This figure shows the following information:
re-analysis of "Bluenose" photo survey
|95% confidence intervals||Population estimate, post-calving photo survey||95% confidence intervals|
Based on recommendations of the Wildlife Management Advisory Council (NWT), the Gwich'in Renewable Resources Board, and the Sahtu Renewable Resources Board, co-management boards in the herd’s range, all non-aboriginal hunting of the Bluenose-West Herd ceased in 2006. The co-management boards made further recommendations to restrict aboriginal harvesting of the Bluenose-West Herd by establishing a total allowable harvest and the requirement for a tag to harvest, measures that were implemented in 2007.Reference 97
Woodland caribou, boreal population
This section is based on the 2011 scientific assessment and 2012 recovery strategy for the woodland caribou (Rangifer tarandus caribou), boreal population.Reference 109, Reference 180Note that this information has been updated since the release of the ESTR national thematic report, Woodland caribou, boreal population, trends in Canada.Reference 181
Woodland caribou are distributed throughout the boreal region of Canada.Reference 182 There are two genetically distinct varieties, or ecotypes, of woodland caribou: 1) forest-dwelling woodland caribou, which are non-migratory and live in relatively small groups year-round in the boreal forest; and 2) forest tundra woodland caribou, which are migratory and live in large herds and winter in the boreal forest. The forest-dwelling ecotype of woodland caribou is made up of ten geographically distinct populations – the boreal population (referred to as “boreal caribou”), which is found through most of the Taiga Plains Ecozone+, is the most widespread. In 2002, COSEWIC assessed the boreal caribou as ThreatenedReference 183 and boreal caribou were added to Schedule 1 of the federal Species at Risk Act.Reference 184
The range of the woodland caribou, including the boreal population, has retracted significantly from historical distributions. The southern limit of distribution has progressively receded in a northerly direction since the early 1900s, a trend that continues to the present day.Reference 109, Reference 183, Reference 185-Reference 187
Taiga Plains Ecozone+ status and trends
Boreal caribou primarily inhabit Canada’s boreal, rather than taiga, ecozones+, with the exception of the Taiga Plains Ecozone+, which provides some of the largest tracts of habitat for these at-risk caribou. This is due to the prevalence of mature or old growth coniferous forests and peatlands, the preferred habitat of boreal caribou.Reference 188 Studies have shown that treed fen and bog peatlands are crucial to the survival of boreal caribou in northern Alberta. This finding would apply to the entire zone of sporadic permafrost that reaches into northern BC and southern NWT (Figure 16).Reference 189 Fifteen boreal caribou local populationsReference * (or components thereof) occur in the Taiga Plains Ecozone+. Of these, 33.3% (n=5) are in decline, 6.7% (n=1) are increasing, and the status of the remaining 60% (n=9) is unknown (Figure 35).
Causes of declines
Broad-scale range recession and population declines of boreal caribou in most areas are associated with human settlement and industrial resource extraction due to the loss, degradation, and fragmentation of their coniferous-forest habitat.Reference 187, Reference 190-Reference 192 Proximate causes of decline associated with landscape-level habitat change include increased predation,Reference 109, Reference 193, Reference 193-Reference 197 increased access by hunters,Reference 190, Reference 194 and linear disturbance.Reference 198, Reference 199 Weather and climate change may affect several aspects of boreal caribou ecology by combining with other threats in complex ways that magnify the principle causes of decline.
In the Taiga Plains Ecozone+ boreal caribou populations known to be in decline have relatively small ranges in the southern part of the ecozone+ (Figure 35).
Table 7 presents an analysis of the proportion of disturbance, both from fire and from anthropogenic sources (defined in the caption), on the ranges of each of the populations completely or partially in the Taiga Plains Ecozone+. This analysis indicates that 57 to 87% of the range of each population that is known to be declining is classified as “disturbance”, with the populations in BC and Alberta having the highest degree of anthropogenic disturbance (see also Figure 6 in the Forest biome key finding). Fire is the main cause of disturbance for the populations in the NWT. Boreal caribou can shift their range use to avoid burned areas provided sufficient old-growth forest remains. Although fire may have short term adverse effects, large fires prepare the conditions for future large, even-aged stands of mature forest that are vital to boreal caribou. In a healthy ecosystem, as one large tract of habitat is disturbed by fire, another is reaching maturity.
|Population Status||Local population or|
unit of analysis
|Local Population Range Disturbance|
|Local Population Range Disturbance|
|Local Population Range Disturbance|
Total % of Disturbance
|not available||BC Maxhamish||0.5||57||58|
|not available||BC Calendar||8||58||61|
|decline||BC Snake Sahtaneh||6||86||87|
|not available||BC Parker||1||57||58|
|not available||BC Prophet||1||77||77|
|decline||AB Caribou Mountains||44||23||57|
Population status is taken from Figure 35 . Note that the ranges of some of the populations extend into neighbouring ecozones+
“Fire %” is the percent of the range area burned within the past 40 years (since 2010). Fire data from the Canadian Large Fire Database, augmented by additional coverage for the Northwest Territories and Parks Canada, that contained wildfires >2 km2 were also used.
“Anthropogenic %” is the percent of the range area affected by anthropogenic disturbance, based on mapping conducting by the Landscape Science and Technology Division of Environment Canada in collaboration with Global Forest Watch Canada (GFWC). All visible linear and polygonal anthropogenic disturbances were digitized from Landsat images. Linear disturbances included roads, railroads, seismic lines, pipelines, power transmission lines, airstrips, dams and other/unknown; polygonal features included settlement areas, mines agricultural areas, cutblocks, oil and gas activities , well pads and other/unknown. All features in the database were buffered by 500 m to create a “zone of influence”, and merged to create a non-overlapping coverage of all anthropogenic disturbances.
This section draws from Trends in breeding waterfowl in Canada,Reference 200 a technical thematic report prepared for the 2010 Ecosystem Status and Trends Report. Analyses of trends by ecozone+ in the waterfowl report included data up to 2006 and have not been updated.
Waterfowl population composition and abundance in the Taiga Plains Ecozone+ is surveyed by the joint Canadian Wildlife Service and US Fish and Wildlife Service waterfowl breeding survey that was established in 1955.Reference 201 Long-tailed duck (Clangula hyemalis), scoters (combined white-winged scoter (Melanitta fusca), surf scoter (M. perspicillata) and black scoter (M. nigra), scaup (combined lesser scaup (Aythya affinis) and greater scaup (A. marila)), northern pintail (Anas acuta), mallard (A. platyrhynchos), and American wigeon (A. Americana) show declining population trends (Table 8, Figure 36, and Figure 37). These populations overlap during breeding, whereas most have different wintering areas,Reference 202 suggesting that the reasons for their declines may be associated with this ecozone+. Waterfowl are patchily distributed across the ecozone+ and trends are also variable from location to location, as shown for scaup in Figure 38.Reference 203
|Species||Nesting habitat||Trend (%/yr)||PNote 1 of Table 8||Annual Abundance Index|
|Annual Abundance Index|
|Annual Abundance Index|
|Annual Abundance Index|
|Annual Abundance Index|
|Long-tailed duck||Ground||-4.164||*Note 2 of Table 8||42.6||30.6||12.5||11.6||-72.8|
|Scoter (white-winged, surf, and black)||Ground||-4.089||*Note 2 of Table 8||250.3||233.1||86.4||87.9||-64.9|
|Scaup (lesser and greater)||Ground||-3.273||*Note 2 of Table 8||951.8||744.5||427.6||384.3||-59.6|
|Northern pintail||Ground||-2.722||*Note 2 of Table 8||94.5||69.3||37.6||44.7||-52.7|
|Mallard||Ground||-2.155||*Note 2 of Table 8||232.9||237.2||168.8||131.6||-43.5|
|American wigeon||Ground||-2.024||*Note 2 of Table 8||194.1||185.5||119.7||121.7||-37.3|
Notes of Table 8
Note: no value indicates not significant
Source: Fast et al., 2011Reference 200
Source: Fast et al., 2011Reference 200
Long description for Figure 36
These two line graphs show the following information:
|Year||Scaup||Scoter||Bufflehead||Canada Goose||Long-tailed duck|
Source: Fast et al., 2011Reference 200
Long description for Figure 37
This line graph shows the following information:
|Year||American wigeon||Green-winged teal||Mallard||Northern pintail|
Despite their abundance, total populations of greater and lesser scaup have been declining since the mid-1980s, with most of the decline being for those breeding in the western boreal forests (Figure 39). Population growth rate for lesser scaup may be most sensitive to adult female survival during the breeding and non-breeding seasons, and, to a lesser extent, to nesting success, duckling survival, and juvenile survival.Reference 204 This suggests that changes to breeding habitat may greatly influence population growth.
The reasons for the declines of these waterfowl populations are not well understood, as very few waterfowl studies have been conducted in the Taiga Plains. Climate change may play an important role, especially for late-nesting long-tailed ducks, scoters, and scaup.Reference 206, Reference 207 As photoperiod is likely the main breeding cue for these species, mismatches in timing may be occurring between their relatively fixed late nesting dates (but see Anteau and Afton, 2009Reference 208) and invertebrate phenology, which is driven by temperature and has likely changed recently due to climate warming.Reference 209 The mismatch hypothesis between breeding birds and changing food supply, although not yet tested in the taiga regions, has been demonstrated elsewhere (for example Thomas et al., 2001Reference 210). The mismatch hypothesis however, is one of many that may explain declines in scaup populations (see review in Austin et al., 2000Reference 211).
Causes of the declines observed for northern pintail, mallard and American wigeon remain unclear. These species fluctuate greatly between years, and some have declined in other regions as well. Canada goose and green-winged teal populations show no statistically significant trends.
Three fishes in the Taiga Plains Ecozone+ are considered at risk in the Northwest Territories: the shortjaw cisco (Coregonus zenithicus) is classified “at risk” and the bull trout (Salvelinus confluentus), and inconnu (Stenodus leucichthys; Upper Mackenzie River and Great Slave Lake stocks only) are classified as “may be at risk”.Reference 212
In 1987, COSEWIC designated the shortjaw cisco as Threatened based on the reduced population and level of habitat exploitation across Canada. The rating was confirmed during a status review in 2003.Reference 213 In the NWT, the shortjaw cisco inhabits Great Slave Lake, which is at the northern edge of its known range; there are also unconfirmed reports of the species in Great Bear Lake.Reference 212 Population status and trends in the ecozone+ are poorly known.Reference 213
The presence of bull trout was confirmed in the early 2000s in the Sahtu region of the Taiga Plains, extending its previously known distribution northward by 4° latitude.Reference 214 Bull trout, which are likely quite widely distributed in high gradient streams and rivers of the south-central Mackenzie River Valley, have been shown to be highly sensitive to a variety of individual and cumulative anthropogenic impacts; many populations south of the ecozone+ have been extirpated or may be threatened.Reference 214
In the upper Mackenzie and Great Slave Lake, inconnu populations appear to have been decimated by net fisheries close to their spawning rivers.Reference 215 Elders recount that their demise began when the flourishing fur trade in the 1940s and 1950s demanded large amounts of feed for dog teams.Reference 216 The decline continued with commercial fishing and loss through bycatch by the lake whitefish fishery in Great Slave Lake. Conservation measures, now in place for many years, have yielded only a slow recovery.Reference 215
Baseline information on fish stocks is summarized in the Mackenzie Basin report on the state of the aquatic environmentReference 59 and through the NWT Environmental Audit and the Cumulative Impacts Monitoring Program.Reference 217 The status for most fish stocks, where data are available, is considered to be stable or increasing. In Great Bear Lake, the lake trout population declined between the early 1970s and the mid 1980s. Quotas were assigned in 1987. Since then, the lake trout harvest has been much lower than the maximum sustainable yield (Figure 40). Arctic grayling stocks in the upper Mackenzie River Basin were adversely affected by a warm-water-induced outbreak of waterborne pathogens in 1989, but stocks appear to have recovered to their former levels, based on information related to sports fisheries, for example, on the Kakisa River (southwest of Great Slave Lake).Reference 217
Key finding 18
Theme Habitat, wildlife, and ecosystem processes
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.
Ecozone+ key finding: Overall, primary productivity increased on 22.7% and decreased on 1.5% of the land area of the Taiga Plains from 1985 to 2006. Increased primary productivity was mainly in the north part of the ecozone+, where studies show increased growth of shrubs, along with some impairment of growth of lichens and of some white spruce. The large fires characteristic of the ecozone+ influence primary productivity but do not account for the overall increase.
This section is based on analyses and interpretations in Monitoring biodiversity remotely: a selection of trends measured from satellite observations of Canada.Reference 13 Additional material has been added on the relationship with forest fires, forage quality, and on aquatic productivity.
The Normalized Difference Vegetation Index (NDVI) measures vegetation vigour due to chlorophyll activity, or “greenness”. Changes in NDVI over the period 1985 to 2006 were examined by Ahern et al., 2011Reference 13 for each ecozone+, based on the findings of Pouliot et al., 2009Reference 218 Results are shown in Figure 41. Overall, 22.7% of the Taiga Plains Ecozone+ showed a statistically significant (95% confidence limits) positive change and 1.5% showed a significant negative change in NDVI.
In the northern Taiga Plains, the extensive area of strong NDVI increase visible in the map corresponds to a large area of conifer forest north of Great Bear Lake to the east of the Mackenzie Valley. A similar but smaller patch lies in the lower Mackenzie Valley. Further south, areas of increasing NDVI are more isolated. The area of decreasing NDVI west of Great Slave Lake does not correspond to any recent burns. The region has a high water table and areas previously vegetated with forest and tall shrubland have been flooded during years of high precipitation.Reference 216
Pouliot et al., 2009Reference 218 also examined the influence of climate and land cover change on the observed NDVI trends in eight regions of Canada. Climate influence was examined by analyzing, on a grid basis, correlations between monthly temperature and precipitation data (Mitchell 2005 in Pouliot et al., 2009Reference 218) and annual peak NDVI. This analysis suggested that NDVI in the Taiga Plains is strongly influenced by climate, more so than in any other region in Canada. As in other northern regions, NDVI was negatively correlated with precipitation and positively correlated with temperature.Reference 218
Olthof et al., 2008Reference 219 examined NDVI trends in a portion of the Taiga Plains Ecozone+ (as well as tundra areas to the north) using the same dataset used by Ahern, 2011Reference 13 and Pouliot, 2009Reference 218 along with higher resolution Landsat data. They found that lichen-dominated communities had consistently lower NDVI trends than vascular-plant-dominated communities, though all showed increasing trends. This is consistent with ground studiesReference 220-Reference 224 and was attributed to increasing vigour and biomass of vascular plants and some impairment of lichen growth due to drying.Reference 219 White spruce in this northern region also show signs of decreased growth rates, likely related to drought stress (see the Forest biome key finding and Figure 8).
In the boreal forest, using satellite-based measurements to index primary productivity is complicated by the effects of forest fires. Productivity is decreased for about a decade following a forest fireReference 225 and then post-fire succession vegetation or age of the trees can also complicate interpreting remote sensing measured trends in plant productivity.Reference 226, Reference 227 Ahern, 2011Reference 13 analyzed the changes in NDVI in relation to fire history across Canada: NDVI trends were negative in areas recently affected by fire (1994 to 2004), positive in areas affected by fires from 1980 to 1990 (where regeneration would have dominated), and generally positive or close to zero in areas affected by fire prior to 1980 (1960 to 1980). The authors concluded that, in the northern portion of Canada’s forested zone, many of the observed changes may be a result of the natural cycle of fire and succession, however, trends in wildfire alone cannot account for the scale and the distribution of the change in NDVI observed over the 22-year period.
Trends of increasing plant productivity as indexed by satellite-based measures (NDVI) may not translate into an increase in forage quality for herbivorous insects or mammalian herbivores. One interacting factor, for example, is that the amount of solar radiation (or cloud cover) and temperature also affect the levels of compounds such as tannins in plants, which affects forage quality.Reference 228 Thus the conditions that promote greater primary productivity may also lower the quality of some of the vegetation as food for herbivores.
Key finding 19
Theme Habitat, wildlife, and ecosystem processes
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.
Ecozone+ key finding: Natural disturbances in the Taiga Plains show signs of change related to climate. On a decadal basis, the area of forest burned increased from the 1960s then declined again in the most recent decade, though data are incomplete for this latter decade. There are indications of a trend to more fires earlier in the season, a pattern consistent with the observed temperature trends. The main forest insect pest, spruce budworm, is endemic in the southern part of the ecozone+ and there are indications that it may be moving northward. Both the forest tent caterpillar and the mountain pine beetle, relatively new to the ecozone+, show signs of becoming more abundant and expanding northward.
The interest in monitoring trends in forest fires has increased recently because of the relationship between a warming climate, fires, and the implications for carbon cycling and storage. People in the communities take note of increases in fire frequency in relation to warmer temperatures. However, it is unclear whether the reported frequency or landscape patterns of fire are different from in the past. For example, 90 fires were reported in the Fort McPherson area in 2003, a hot, dry summer,Reference 129 but it is difficult to interpret this in terms of long-term trends because the number of fires and the area burnt annually is highly variable – a few years can be expected to have exceptionally high rates. The Taiga Plains experienced large fires in the 1940s, a warm and dry decade, as documented, for example, in the Fort Smith area.Reference 229 In a Fort Providence study of fire history over the 19th and 20th centuries, the highest proportion of forest stands began their growth following the extensive fires in the 1940s.Reference 230 Few trees survived fire beyond 200 years. In addition to the 1940s, the 1860s, 1880s, and 1920s were decades in which large areas were burned.
Patterns of human involvement with fire have changed with changes in settlement, cultural and economic practices: both patterns of accidental or deliberate fire ignition and those of fire suppression. For example, in the past, aboriginal people in the central and southern part of the ecozone+ used burning as a management tool to improve conditions for important food sources such as moose, wood bison, hare, beaver, grouse, and berries that thrive in early successional habitats.Reference 216, Reference 230, Reference 231 This resulted in a landscape that included grasslands that have since reverted to forest.Reference 232
Fire behaviour in the boreal forest is partly related to the age of the tree stands.Reference 233 After a rapid increase over the first few decades, flammability decreases and remains at a lower level in the mature forest, rising again as the stand deteriorates. Short fire intervals promote regrowth of deciduous trees over conifers. Intense fires in young conifer stands clear areas that can then become deciduous stands, via seeds that can travel long distances by wind. Variation in the depth of burn results in great differences in seedling density. A warmer, drier climate with increased fire frequency will result in more severe, deeper fires that burn soil organic matter and kill more below-ground plant parts than light surface fires.Reference 233
The discussion below summarizes recent trends in fire extent, duration and timing. It is based on Trends in large fires in Canada, 1959-2007,Reference 13 a technical thematic report prepared for the 2010 Ecosystem Status and Trends Report. Data used in analyses for the report were current to 2007 and have not been updated.
Some of the largest fires in the country occur in the Taiga Plains Ecozone+.Reference 234, Reference 235 This is due to a combination of factors, including the dry, continental climate;Reference 236 the remote location with little suppression effort;Reference 234 and, a dominance of boreal fuel types with relatively high average fuel loads that lead to higher consumption rates.Reference 237, 2Reference 238 These factors result in relatively severe fires that burn over large areas.
On average an area of 2,858 km2 burns each year, with great variability from year to year (Figure 42). In many years the annual area burned (by fires over 2 km2) is less than 100 km2, while in other years it can be very high – 17,354 km2 burned in 1995. Some low values early in the period of record may be due to limited monitoring in this northern ecozone+, but this trend continues into recent decades, validating the occurrence of very low fire years (see, for example, 1991, 1997 and 2002 in Figure 42). In comparison with other ecozones+, the average annual area burned is high (0.71% of the forested ecozone+ area, second only to the Taiga Shield), despite the frequency of very low fire years.Reference 10
Note: this fire trend is based on large fires (fires over 2 km2 in size, rather than the total area burned).
Long description for Figure 42
This bar graph shows the following information:
|Year||Area burned (km2)|
The long-term trend in area burned is similar to trends at the national level. Area burned is shown by decade since the 1960s in Figure 43 and the fires are mapped in Figure 44. Area burned increased from the 1960s until the 1990s and then fell sharply in the 2000s. As noted above, the low numbers at the beginning of the record may be attributed to data collection techniques that improved starting in the 1970s.Reference 236Although the numbers for the 2000s should be considered with caution since they do not include a full decade, the recent decline may be related to changes in large atmospheric oscillations.Reference 10
The value for the 2000s decade was pro-rated over 10 years based on the average from 2000-2007
Long description for Figure 43
This bar graph shows the following information:
|Decade||Area burned (km2)|
Duration and timing of fires
The average duration of active large fire occurrence is 81 days (about 4 months), which has not changed significantly. This is different from the fire season duration, which is calculated based on fire weather indices and is longer, at approximately 173 days.Reference 239 The fire season is the period of time that the weather is conducive for fires to occur. The numbers documented here are based on the actual occurrence of large fires. Based on this analysis, fires most commonly occur in June through to August, but can occur as early as April and as late as September (Figure 45).
The average duration of the period of fire occurrence has not changed over time but the distribution of fires within the fire season has undergone some subtle changes over the last four decades. The proportion of fires that occur in April has shifted from zero in the 1960s to 1.2% in the 1990s. The proportion of fires that occur in May has been steadily increasing, a statistically significant change (R2=0.93, p=0.035). All fires that were reported in April were human caused; those in May were equally distributed between being caused by humans or lightning. Early-season fires may also occur in dry years when fires from the previous season have smoldered in deep layers of peat throughout the winter, re-emerging as surface fires in the spring.Reference 216 More data are needed to determine if these small changes are the start of a lengthening of the fire season or are artifacts of the large fire database limitations.
Note: this fire trend is based on the number of large fires over 2 km2 in size.
Long description for Figure 45
This clustered bar chart shows the following information:
There were no changes in how fires were distributed among the latter months of the fire season, with late-season fires being predominantly caused by lightning, the cause of 83% of Taiga Plains Ecozone+ large fires (Figure 46 a). The proportion of fires caused by lightning in comparison to those caused by humans increased from the 1960s to the 1990s (Figure 46 a). The total area burned as a result of lightning ignitions also increased over the 40 year period (Figure 46 b). This increase in area burned by lightning is most likely due to warmer temperatures during the fire season in the 1990s.Reference 239, Reference 240
Large fires are defined as over 2 km2.
Long description for Figure 46
These two bar graphs show the following information:
|Decade||Total human (Percentage)||Total lightning (Percentage)||Area human (km2)||Area lightning (km2)|
Trends in large-scale native insect outbreaks are correlated with weather conditions and forest fires, both of which influence the likelihood of insect outbreaks. Insect outbreaks can repeatedly defoliate trees, causing failure of the trees to reproduce (produce cones) and causing reduction in growth and vigour. Additionally, multi-species infestations may further damage trees already weakened by an initial attack. Significant insect pests in the ecozone+ are spruce budworm (Choristoneura fumiferana), larch sawfly (Pristiphora erichsonii), and forest tent caterpillar (Malacosoma disstria).
Spruce budworm, by far the most serious pest in the Taiga Plains Ecozone+, is a small moth known for severe and extensive outbreaks causing heavy defoliation in fir and spruce trees, particularly in the boreal forest.Reference 241 The outbreaks can last 5 to 15 years and populations can reach extremely high densities.Reference 242 Outbreaks of the spruce budworm are closely tied to climate, although the specific weather factors favouring outbreaks are not well understood.Reference 243 Outbreaks are initiated by tight synchrony between the larvae forming feeding sites and the tree’s developing buds. Spring frosts can affect the buds and cause budworm collapsesReference 244 and frosts probably limit the northern distribution of the budworm.
In the NWT, a recent outbreak was severe. At its peak (2002), the budworm moderately or severely defoliated approximately 24,000 km2 of white spruce.Reference 243 Although this outbreak collapsed throughout most of the NWT between 2003 and 2005, it has persisted in and moved progressively further north in the Sahtu (Norman Wells) region.Reference 46, Reference 115
Spruce budworm outbreaks in the Fort Nelson area are concentrated in mature white spruce stands and aspen/spruce mixed stands.Reference 241 Based on analysis of tree rings, outbreaks in this part of the ecozone+ occur on average every 26 years, with five to six outbreaks in the 20th century. The most recent outbreak extended from about 1987 to 2003.Reference 245, Reference 246
Forest tent caterpillar is a hardwood defoliator, in particular attacking trembling aspen. Otvos et al., 2010Reference 247 analyzed the six outbreaks that have occurred since the start of detailed record keeping in 1944 in British Columbia. They found that outbreaks have become larger in extent and longer in duration. Forty-six percent of aspen defoliation in the province (resulting from all six outbreaks combined) occurred in the boreal white and black spruce biogeoclimatic zone. The outbreak in the 1990s was concentrated around Fort Nelson.Reference 246
The NWT experienced its first outbreak of forest tent caterpillar in the mid-1990s in the Liard Valley in the southwest corner of the NWT part of the ecozone+.Reference 248 The outbreak lasted two to three years, peaking in 1996.Reference 248 As forest tent caterpillar eggs are susceptible to mortality during winter cold spells,Reference 249 the strong trend to warmer winters experienced in the Taiga Plains over the past 50 years has likely contributed to the increase in tent caterpillar outbreaks in the ecozone+.
Mountain pine beetle reached the Fort Nelson Forest District in 2010, spreading along the Kechika River corridor.Reference 250 There are extensive pine plateaus in this region potentially at risk if the infestation increases in intensity and extent.Reference 246
Mountain pine beetle is present in the Alberta part of the Taiga Plains Ecozone+, and reached a few kilometers into the Northwest Territories in the summer of 2012.Reference 251 Infestation levels in the northern part of Alberta are low relative to the most affected area in the centre of the province.Reference 252 However, surveys of the ratio of new infestations to infestations from the previous year in Alberta, conducted in the summer of 2010, showed that the beetle is spreading in the north.Reference 252 A survey of winter mortality conducted the following spring (2011) concluded that there was a high survival rate of beetles, leading to forecasts of further increases in beetle infestation.Reference 253 Beetles were first detected in the west-central part of Alberta in 2006, rapidly becoming abundant and spreading east.Reference 252 There have been localized outbreaks of mountain pine beetle in Alberta in the past, including small pockets of infestations in the north since 2001.Reference 254
The mountain pine beetle’s preferred host is mature, even-aged pine standsReference 250 – thus forest management practices, including fire suppression, have an impact on the spread of this insect pest. Climate is also an important factor: temperatures of -40°C are required to cause sufficient winter mortality to result in declines.Reference 254 While the mountain pine beetle is likely at the far northern limit of its range in the Taiga Plains under current climatic conditions, there is potential for more serious eruptions and further expansion of its range under future climate change.Reference 255
Key finding specific to ecozone+
Wildlife disease and parasites
Theme Habitat, wildlife, and ecosystem processes
Ecozone+ key finding: Wildlife disease is of importance to the Taiga Plains Ecozone+ for ecological, economic, and human health reasons. Bovine tuberculosis and brucellosis affect a high percentage of wood bison and present risks to human health and to economic activities. There is emerging evidence and growing concern that some wildlife diseases and parasites (including anthrax, ungulate parasites, and viruses and funguses affecting frogs) may be increasing in prevalence and/or range, or may do so in the future, in response to warmer weather and changes in wildlife species distribution.
The status of wildlife health in the Taiga Plains is mostly undescribed although the knowledge base is starting to improve through community-based monitoring, at least for wildlife species important to people. For example, the status of caribou health in parts of the ecozone+ was monitored through hunters working with biologists and veterinarians from 2003 to 2008. Hunters and Elders were interviewed to document their local ecological knowledge of wildlife health and local hunters were trained as monitors to collect tissue samples and measurements to assess body condition and monitor health of harvested caribou (n=69) and moose (n=19). In 2007 the program was extended to include participation in the annual caribou hunt held by one community.Reference 256
Changes can be expected in disease and parasites in the ecozone+ from two climate-change-related factors:
- Temperature dependency of parasites and pathogens for some diseases. For example, moose tick outbreaks in Alberta are known to coincide with warmer temperatures in spring and with earlier snow loss.Reference 257
- Expansion of the range of endemic species or the colonization of regions of the ecozone+ by non-native species. An example is the spread of muskoxen into the northeast Taiga Plains starting in the 1990s from northeast of Great Bear Lake where the muskoxen were known to be infected with a lungworm. In this example, there was a concern that the muskoxen could pass the infection to Dall sheep. However, studies showed that infection across species did not occur under experimental conditions.Reference 258
This section draws from Wildlife pathogens and diseases in CanadaReference 11 and Northern caribou population trends in Canada,Reference 97 technical thematic reports prepared for the 2010 Ecosystem Status and Trends Report.
Diseases affecting ungulates
Bovine tuberculosis (BTb) is caused by infection with the bacterium Mycobacterium bovis. It readily infects domestic cattle, and in people it causes a disease indistinguishable from human tuberculosis (infection with M. tuberculosis). Infected animals, meat products, and milk are significant health hazards for people, and for public health reasons, BTb was successfully eradicated from Canada’s domestic animal population through a long and costly program of testing all herds and slaughtering entire herds in which any infected animals were detected.
Bison in Wood Buffalo National Park and adjacent areas became infected with BTb in the 1920s (see section on wood bison in the Species of special interest key finding on page 54). Infection has persisted in this herd and surveys between 1997 and 1999 found that approximately 49% of these bison were infected.Reference 259 In the past two decades, other populations of wild bison, apparently free of infection with BTb, have become established in the Taiga PlainsReference 260 (Figure 31). Measures to prevent the spread of BTb to these infection-free herds are not fully effective and the disease has spread west in recent years.Reference 163, Reference 261 Thus, the potential spread of BTb from infected to non-infected wild bison, all of which are assessed as Threatened by the Committee on the Status of Endangered Wildlife in Canada, and also to livestock, is a major conservation and socio-economic issue.
Brucellosis is the name given to all diseases caused by infection with any of the several different species of the bacterial genus Brucella. The clinical manifestations of brucellosis are many, but the most common are infection and inflammation of the female and male reproductive tracts with resulting abortion and male infertility, and infection of joints and tendon sheaths resulting in progressive lameness. Infection persists, often for the lifetime of the animal. People are similarly susceptible to infection with Brucella sp., and brucellosis in animals with which people have contact is a public health risk.Reference 262-Reference 264
Infection with Brucella sp. is of potential ecological and public health significance in bison in and around Wood Buffalo National Park, where the bison populations infected with bovine tuberculosis are co-infected with bovine brucellosis caused by Brucella abortus.Reference 265 Approximately 30% of bison in Wood Buffalo National Park area are infected.Reference 259
Brucella suis biotype 4 is present in barren-ground caribou in northern Canada:Reference 263 20 to 50% of animals in various herds are infected.Reference 266, Reference 267 However, the ecological impact, if any, on infected populations is not known. Infection of northern people with this bacterium occurs and is associated with consumption of caribou.Reference 263, Reference 264 Whether or not B. suis biotype 4 is a naturally occurring pathogen in North America or a pathogen introduced from Europe in imported reindeer also is not known. There are no records of this infection in woodland caribou.
As noted for bovine tuberculosis, it seems certain that without effective intervention of some form bovine brucellosis will spread to non-infected wild bison herds progressively over time, and that the vast majority of wild bison in Canada then will be infected.Reference 260 This will place bison recovery efforts further at odds with livestock economies and public health interests. Too little is known about the ecology of Brucella in caribou to identify current trends or predict future trajectories.
Anthrax is the name given to all forms of disease caused by infection with the bacterium Bacillus anthracis. It is most typically a disease of wild and domestic ungulates, in which it usually is rapidly fatal. Mammalian predators and scavengers also die regularly during anthrax outbreaks in ungulates. Humans are susceptible to anthrax and disease in people ranges from a self-limiting infection of the skin to fatal disease. Ungulates generally become infected from bacterial spores in soil. Environmental conditions that cause these spores to persist for decades or even centuries in soil and to concentrate on the soil surface, such as high-calcium soil chemistry for spore persistence, and flooding followed by dry periods for spore concentration, appear to be major risk factors in outbreaks of anthrax in wild and domestic ungulates. Animal to animal transmission of the bacterium plays only a minor role. Anthrax probably was introduced to North America by European exploration and settlement.Reference 268-Reference 270
In Canadian wildlife, anthrax has been recognized most often in bison in and around Wood Buffalo National Park. The first recognized outbreak was in 1962 and sporadic outbreaks have occurred ever since, often with inter-outbreak time spans of many years (see the wood bison section of the Species of special interest key finding on page 54). The total number of bison and other species to have died of anthrax is unknown, but a minimum of 1,309 bison in the Taiga Plains died of the disease in outbreaks between 1962 and 1993 and a 2012 outbreak killed 440 bison.Reference 166 The occurrence of outbreaks in wild bison and in livestock appear linked to climatic factors, particularly intense precipitation followed by drought. To date, no predictive models have been published with respect to outbreaks of anthrax in Canada and predicted climate change.
The bacterium causing Johne’s disease, known for causing chronic wasting and diarrhea in cattle, has been found in caribou from Greenland and was found at low levels in Bluenose-West caribou in 2008.Reference 271 The bacterium has also been found in wood bison.Reference 272
Parasites affecting ungulates
Besnoitia is a genus of protozoan parasite which develops pin-head sized cysts in the skin and connective tissues of its herbivore intermediate host and typical coccidial forms in the intestines of its carnivore definitive hosts. No disease due to Besnoitia has been recognized in definitive hosts, but intermediate hosts sometimes develop disease conditions associated with severe infections.Reference 273 In Canada, Besnoitia tarandi infects caribou and probably muskoxen. Infection is very common in barren-ground caribou and has been described in woodland caribou.Reference 274, Reference 275 Although occasional severe manifestations of infection on the skin have been seen, most infections appear to have little or no health consequences for these species.
The status of Besnoitia, assessed from caribou harvested in the fall from 2007 to 2009 from several Canadian herds, was variable, with the Bluenose-West Herd having an infection rate in the range of 30 to 45%.Reference 276
Throughout most of their range in North America, moose suffer periodic events of high mortality in late winter associated with severe infestations with winter tick, Dermacentor albipictis. This tick is native to North America and infests other hosts including woodland caribou and bison. However, severe infestations frequently resulting in death are common only in moose. Winter ticks occur in the southern Taiga Plains ecozone+,Reference 277 and have recently been found further north in the Mackenzie Valley between Tulita and Fort Good Hope.Reference 278, Reference 279
Weather events affect the abundance of the ticks, particularly conditions in April when gravid adult female ticks drop to the ground and may survive to lay eggs, thus affecting the numbers of larvae available to infest moose the following fall. Environmental conditions also affect the resilience of the moose, particularly conditions in late winter and early spring the following year when infested moose must endure the ticks. There are not sufficient historical records to determine if there are trends in winter tick infestations and their effects on moose populations. Hunters along the Mackenzie River in the Northwest Territories have recently observed moose in the spring with severe hair loss typical of winter tick infestation, a phenomenon new to the Traditional Knowledge of First Nations in the region.Reference 280
Diseases affecting amphibians
Frogs are at the northern limit of their distribution in the Taiga Plains. Pathogens that are affecting amphibians globally have recently been detected in the ecozone+.
- Ranaviruses, lethal viruses responsible for die-offs of amphibians world-wide wideReference 281 have recently been found in wood frogs in the NWT portion of the Taiga Plains.Reference 282
- Chytrid fungus, Batrachochytrium dendrobatidis (Bd), which infects the skin of amphibians, has been linked to catastrophic amphibian declines around the world since the 1990s.Reference 283 There is strong evidence linking Bd to the declines of amphibian species in western North America.Reference 284, Reference 285 Bd was found in samples at a single site in the Taiga Plains in a 2007 to 2008 study,Reference 282 but was detected in all three species of amphibians in the survey area (wood frogs, boreal chorus frogs, and western toads).
Key finding 20
Theme Habitat, wildlife, and ecosystem processes
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.
Ecozone+ key finding: There is little information on changes in food webs in the Taiga Plains. Abundance of many mammals in the Taiga Plains is cyclic, driven or influenced by food web effects as well as drivers like climate. Changes in small mammal cycles have been reported in other northern regions, and a recent dampening of snowshoe hare and lynx cycles is noted in the NWT. Northern tundra caribou wintering in the Taiga Plains have declined in abundance which may reflect a low period on a population cycle. Declining boreal caribou populations in the south of the ecozone+ may be affected by changes in predator-prey dynamics related to habitat alteration.
Cycles in population abundance
Cyclic abundance is perhaps the best-known feature of community and population dynamics in the Taiga Plains. The amplitude and frequency of cyclic abundance depend on body mass (smaller species cycle at a higher rate). Large-bodied mammals: moose, muskoxen, boreal caribou, and wood bison, do not appear to exhibit cyclic dynamics.
Migratory tundra (barren-ground) caribou wintering in the northern Taiga Plains likely are cyclic in their abundance, based on what is known about herds elsewhere,Reference 127 with the halving time in their herd size being from 5 to 7 years (see Species of special interest key finding on page 59). The Bluenose-West herd has experienced a sharp decline – a drop in abundance from 1992 to 2004 from over 110,000 to about 18,000 caribou – followed by a leveling off at this lower population. This may be a low point in the cyclic patterns of northern caribou abundance. Management actions have been taken to reduce harvest. Continued monitoring will show if altered conditions in the caribou range (for example, changes in fire ecology or in snow condition on winter range)Reference 97 affect the herd’s ability to rebound from the current phase of low abundance.
Typically, the highs and lows in abundance of cyclic mammals can differ by an order of magnitude and vary in timing and extent even between neighbouring regions.Reference 286 Cycles or fluctuations in mice, voles, lynx, and snowshoe hare are well documented (Figure 47 and Figure 48 and Danell et al., 1998Reference 287). The amplitude of the snowshoe hare and lynx cycles has dampened over time (Figure 48). Fluctuations in abundance among grouse and ptarmigan species have also been noted in this ecozone+.Reference 288 Cycles in prey species are linked to cycles in predators, especially for specialized predators (Figure 48). Prey abundance also influences generalist predators such as foxes and they, in turn, influence the abundance of alternate prey species.Reference 289
Climate variability also has a role in entraining spatial and temporal variability in abundance in the boreal forest.Reference 290 However, how climate interacts with direct and indirect effects on mechanisms causing cycles is both complex and only partially understood. Across North America, the amplitude of hare populations in peak years and forest fires (total burned area) are correlated.Reference 291, Reference 292 Changes in climate and fire activity have the potential to affect both the synchrony and the amplitude of hare cycles across large areas in the ecozone+. Murray, 2003Reference 293 reported that synchrony in hare population cycles across North America have recently declined, although the reasons for the decoupling are uncertain. Similarly in northern Europe, the cyclic abundance for grouse, mice and voles as well as the larch bud moth has diminished or disappeared. These collapses may be linked to changes in climate.Reference 294 With the exception of the dampening of the snowshoe hare and lynx cycle in the NWT (Figure 48), changes and collapses in hare and small mammal cycles have not been observed in the Taiga Plains so far, however longer datasets from continuing monitoring programs will be required to detect changes in synchrony and amplitudes of cycles in all northern ecozones+.
Based on surveys over 5 nights in August, 100 traps per night.
Source: Environment and Natural Resources, 2012.Reference 295 Data coordinated by the NWT Small Mammal Survey, Government of the Northwest Territories. Participating groups: Ducks Unlimited Canada (Cardinal Lake); Sahtu Renewable Resources Board (Tulita); Gwich'in Renewable Resource Board (Inuvik); Protected Areas Strategy Secretariat (Trout Lake); ENR (all other sites).
Long description for Figure 47
This graphic is composed of three line graphs of a small mammal abundance index and a map that indicates the sampling locations in the north, south and central regions of the Taiga Plains Ecozone+. The three line graphs show the following information:
Predator-prey relations: boreal caribou
There may be impacts on boreal caribou in the southern part of the ecozone+ related to changes in predator-prey relations, in turn related to habitat changes from forest harvest practices and habitat fragmentation, possibly combined with higher rates of areas burned. This is based on the conclusion from several studies that the most significant proximate cause of boreal caribou declines in Canada is increased predation driven by landscape changes that favour younger forests and higher densities of alternative prey (moose and deer, in this part of the ecozone+).Reference 181 Boreal caribou are declining in the southern part of the ecozone+ (see the Woodland caribou, boreal population section of the Species of special interest key finding on page 60).
Aquatic food webs
Food webs are complex and the first indications of significant changes can be through indirect, unpredictable effects. In aquatic ecosystems, food web changes are a suspected cause of increases in some contaminants (or less of a decrease than would be expected, based on declines in legacy contaminants elsewhere). This has been proposed as one explanation for contaminant levels and trends in Great Slave LakeReference 123, Reference 296 (see Contaminants key finding). In the Boreal Cordillera, this effect was demonstrated for lake trout: differences in the food web compared with neighbouring lakes (related in part to fishing pressure) resulted in a higher degree of biomagnification of organochlorines Lake Laberge in the southern Yukon.Reference 297, Reference 298
Other factors that can be expected to alter aquatic food webs (and may be altering them now) include warmer water temperatures, resulting in changes in fish distribution in streams. The extent of thaw slumping (slope failure from thawing of ground ice) is increasing in Mackenzie Delta lakes, and is leading to changes in aspects of water quality that determine biotic communities, with an expected consequence of shifts in aquatic food webs (see Wetlands key finding on page 18).
- Footnote *
A boreal caribou local population is a group of boreal caribou occupying a defined area distinguished spatially from areas occupied by other groups of boreal caribou. Local population dynamics are driven primarily by local factors affecting birth and death rates, rather than immigration or emigration among.Reference 109
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