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Theme: Biomes

Key finding 1

National key finding
At a national level, the extent of forests has changed little since 1990; at a regional level, loss of forest extent is significant in some places. The structure of some Canadian forests, including species composition, age classes, and size of intact patches of forest, has changed over longer time frames.

Forest extent

Forest was once the most common land cover type found in the Mixedwood Plains Ecozone+. Estimates of the amount of land historically cleared by Aboriginal peoples within the ecozone+ are not available, but Jenness12 estimated that cornfields were planted as far as 3.7 km on either side of villages of Iroquoian speaking peoples in Ontario. By the time European settlers arrived in the 18th and 19th centuries, much of the land already cleared had returned to forest cover after Aboriginal populations were devastated by epidemics and warfare.13 Most of the forest in the Quebec portion of the ecozone+ was harvested between 1800 and 1880 at a time associated with the first population peak in the area.14,15 At that time, more than 70% of the area was being used for agricultural activities. As a result, many areas were subject to changes in the drainage system, peat extraction, and other soil modifications for agriculture.13,16,17 Forest cover was at its lowest in Ontario around 1920 when it is estimated that only 10.6% forest cover remained.18

Since these times of historic lows in forest cover, the amount of forest in the ecozone+ has increased in both provinces. Currently there is an estimated average 25% forest cover within the Mixedwood Plains; the Prairie Ecozone+ is the only Canadian ecozone+ with less forest cover (0.9%).8 The amount of forest cover varies greatly throughout the ecozone+ from a low of about 5% in Essex County in southwestern Ontario, to a high of 75% in some areas along the northern border of the ecozone+, including the upper Bruce Peninsula19 (Figure 4).  In recent years, whether there has been an increase or decrease in forest cover depends on the area under discussion. In some areas such as the Frontenac Arch (near Westport Ontario and Frontenac Provincial Park), there has been a significant increase in forest cover. The proportion of forest land increased from 29 to 40% between 1934 and 1995.20 The rate of increase between 1959 and 1995 was 3.3% per decade.20 In the St. Lawrence lowlands area of Quebec, forest cover and fragmentation remained unchanged in areas under intensive agriculture for the time period between 1950 and 1997.21,22 In areas less suitable for cultivation, forest cover  increased (26.8% in 1950 to 34.2% in 1997)22 and forest fragmentation decreased due to conversion of old fields into forest because of land abandonment,21,22 a situation similar to that found in the Frontenac Arch of Ontario.20 When forest cover in the entire Quebec portion of the ecozone+ was compared between 1969 and 1995,23 a slight increase of 2.9% was found between the first (1969 to 1975) and the third (1990 to 1995) inventory program (Figure 5 ).23

Figure 4. Land cover of the Ontario portion of the Mixedwood Plains Ecozone+ based on the Southern Ontario Land Resource Information System (SOLRIS) Phase 1 Wooded Areas Mapping (based on year 2000 imagery).
Southern Ontario Land Cover
Long description for Figure 4

This map shows the distribution of five land cover types in the Ontario portion of the ecozone+. Treed areas are predominantly along the northwest edge from the Bruce Peninsula to the Ottawa River. Other natural areas are scattered throughout the region, most notably on the north shore of Lake St. Clair, on the north shore of Lake Erie at Long Point, around a number of lakes between Barrie and Kingston, and in the area east of Ottawa. Most of the built up areas are found around Toronto and Ottawa. The remainder of the region is composed of agriculture, aggregate and other land cover types and water.

Source: Ontario Ministry of Natural Resources, 200619

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Figure 5. Changes in land cover in the Quebec portion of the Ecozone+, 1969–1995.
Land cover type chart
Long description for Figure 5
This bar graph shows the following information: Percentage of cover (approximate)
Land Cover TypeInventory 1 1969-1975Inventory 2 1981-1988Inventory 3 1990-1995
Other Land Cover62%60%60%

Source: Ministère des Ressources naturelles et Faune du Québec, 201023

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Near urban areas such as the Golden Horseshoe around Toronto, forest cover has continued to be lost due to urbanization (though at a lesser rate than agricultural land is being lost).8 Human population density has the strongest correlation with the various indicators of forest fragmentation.24 The major ice storm that hit the St. Lawrence Lowlands in 1998 may also have contributed to forest loss as numerous woodlots were removed due to ice damage.25,26  In eastern Ontario, the ice storm is also believed to have increased forest patch isolation.27

Forest structure

In the central portion of the ecozone+ (within Ontario) diameter limit cutting has led to generally young (< 70 years old), almost even-aged stands.28 Uneven-aged stands are limited to stands managed under the selection system or left uncut in parks or other areas (estimate of 10% or less of remaining forest cover29). These stands contain few, if any, medium or large trees.18,28  In eastern Ontario, the forest is primarily even-aged and even younger than in the central portion of the ecozone+ (average 63.5 years old30). Old-growth forests used to dominate the landscape but they have been replaced with second-growth forests that, due to their young age and management history, lack the structural diversity and complexity of the pre-settlement landscape.18

In Quebec the situation is similar. The forest is dominantly immature (67% regenerating and young stands combined with mature and senescent stands making up 33% of the forested land base. The greatest amount of change in the Quebec portion of the ecozone+ over recent decades is seen in forest age as there has been an increase in mature and senescent forest of 15%, with a decrease in immature forest of 15% between the first and the third inventory program23 (Figure 6).

Figure 6. Changes in percentage forest cover by development stage within the Quebec portion of the ecozone+.
Developement stage chart
Long description for Figure 6
This bar graph shows the following information: Percentage of cover (approximate)
Developmental StageInventory 1 1969-1975Inventory 2 1981-1988Inventory 3 1990-1995
Other Land Cover18%24%33%

Source: Ministère des Ressources naturelles et Faune du Québec, 201023

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Forest composition

The species composition of the ecozone+’s forest has changed greatly since pre-settlement times.13,17,31,32,33 How the species composition has changed depends on the area under study, the disturbance history, and the type of information used to reconstruct historical forest conditions.13,34 However, generally,  research has found that: 1) mature or old-growth forests generally achieved older ages in the past than in the present, as current forests are mostly the result of major human disturbances during settlement; 2) there was more conifer and less deciduous cover in the past than in the present; and 3) early successional species were less common and late-successional species more common than today.14,17, 34,35,36

When more recent changes in species composition were examined in Quebec,23 it was found that the relative wood volume for conifers, white spruce (Picea glauca), black spruce (Picea mariana), white pine (Pinus strobus), and balsam fir (Abies balsamea) all decreased by between 1.1 and 2.3% between 1969 and 1995, while tamarack (Larix laricina), red spruce (Picea rubens), and hemlock (Tsuga canadensis) increased by 1.2, 2.3, and 2.8%, respectively. When deciduous species were examined, white birch (Betual papyrifera), yellow birch (Betula alleganiensis), red oak (Quercus rubra), sugar maple (Acer saccharum), large tooth aspen (Populus gandidentata),and American basswood (Tilia americana) all decreased by between 1.4 and 4.9% between 1969 and 1995, while silver maple (Acer saccharinum) and red maple    (Acer rubrum) increased by 1.2 and 15.4%, respectively. Many of these changes can be attributed to insect outbreaks. Decreases in conifer species composition are associated with insect outbreaks (mainly spruce budworm, Choristoneura fumiferanada) and logging activities.35,36,37 The increase in red maple likely was a result of these disturbances35 combined with its role as an early successional species in those areas where land is returning to forest cover.15 Red maple is a super-generalist species which has low resource requirements and the ability to rapidly capture the available growing space.38,39

The pattern with late successional deciduous species is more complex. Although sugar maple has shown important increases in many regions since European colonization,16,17 its relative importance decreased by 5% over the 1969 to 1995 period. Though decreases in sugar maple are sometimes attributed to the 1998 ice storm which hit both Ontario and Quebec,26 the ice storm occurred after the declines seen in the Quebec data set.23 Since the late 1970s, sugar maple declines and dieback have been observed sporadically at different scales in the deciduous forest of northeastern North America,40,41 and particularly in Quebec.35,42,43  Environmental factors such as extreme climate events, insect defoliation, and the negative impact of acid deposition on soil fertility may all be involved in the recent decline of the sugar maple population in some areas of northeastern North America.44

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Key finding 2

National key finding
Native grasslands have been reduced to a fraction of their original extent. Although at a slower pace, declines continue in some areas. The health of many existing grasslands has also been compromised by a variety of stressors.

Prairies and savannahs

Prairies and savannahs occur only in the southern Ontario portion of the ecozone+ and it is estimated that approximately 82,000 ha (820 km2) were present at the beginning of European settlement.45 The most extensive areas of prairie vegetation occurred in an almost continuous band along the Norfolk Sand Plain, from Turkey Point northward to Brantford and Cambridge, and from there eastward to Hamilton. Other large areas existed along the nearshore areas of Lake St. Clair (Walpole Island and Chatham area) and the Detroit River (Windsor and Amherstburg), as well as the Oak Ridges Moraine in the vicinity of Rice Lake.

Today, prairie and savannah vegetation has virtually disappeared from the Mixedwood Plains Ecozone+ (Figure 7). The largest remaining example, over 900 ha, is found in the Grand Bend–Port Franks area. A further 600 ha remain at Windsor and Walpole Island First Nation. Together, these three large sites represent 1.8% of the estimated original extent in the ecozone+.45 Aside from a few other remnants over several hectares in size, most remaining fragments are less than 0.5 ha, and often in the order of 0.1 ha. The total area of these small fragments is approximately 700 ha. Therefore, together, a total of 2,200 ha (22 km2) of prairie and savannah remain in the ecozone+, representing only 2.7% of the historic extent (and a loss of 97.3%).45,46

Figure 7. Tallgrass prairies, savannahs, and alvars in the Mixedwood Plains Ecozone+.
Southern Ontario Area
Long description for Figure 7

This map shows the distribution of alvars and tallgrass prairies and savannahs in the Ontario portion of the Mixedwood Plains Ecozone+ in 2011. The greatest concentration of alvars is on Manitoulin Island and the Bruce Peninsula. They are also located to the east of Lake Simcoe, north of the western end of Lake Ontario and along the Ottawa River. Alvars are also found in two locations on the west Lake Erie islands. Tallgrass prairies and savannahs are predominantly found in the southern part of the ecozone+, north of Lake Ontario and Lake Erie, with clusters just north of Lake St. Clair and around Port Franks and Windsor. Tallgrass prairies and savannahs are also found in a few scattered locations to the west of Lake Simcoe and on the edge of Severn Sound in Georgian Bay.

Source: Natural Heritage Information Centre, 201147

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This pattern of decline in prairie and savannah vegetation in the ecozone+ is similar to that observed across North America broadly. Approximately 99.8% of both the tallgrass prairie48 and tallgrass savannah of the mid-western U.S. and Canada49 has been lost. No other vegetation type in North America has been so reduced in extent. For that reason, tallgrass prairie and savannah vegetation is one of the most threatened ecosystems in the ecozone+.50

Prairies and savannahs support many plant and animal species considered to be rare in Ontario. As of 2009, there were 726 vascular plant taxa recognized as rare in the province.51 Of these,160 (22%) occur in southern Ontario’s prairies and savannahs. Many rare species of fauna are also present. A number of tallgrass prairie and savannah bird species, including lark sparrow (Chondestes grammacus), greater prairie-chicken (Tympanuchus cupido), and Bewick’s wren (Thryomanes bewickii) no longer breed anywhere in Ontario.52 A number of rare insect species associated with tallgrass prairie, oak savannah, and sand barrens are only known (or were known) from single or a very few sites in Ontario, including barrens dagger moth (Acronicta albarufa), aweme borer (Papaipema aweme), glorious flower moth (Schinia gloriosa), frosted elfin (Callophrys irus), the leafhoppers Chlorotettix fallax, Graminella oquaka, Hecalus flavidus, Paraphlepsius turpiculus, Xerophloea peltata, and the planthopper Fitchiella robertsoni.45,53


Alvars are open grassland, savanna, and sparsely vegetated (rock barren) habitats that develop on very thin soils over flat limestone or dolostone bedrock.54 Almost all of North America’s alvars occur within the Great Lakes basin and the Mixedwood Plains Ecozone+.

Alvars in Ontario

In Ontario, alvars are located on the major limestone plains of the Mixedwood Plains including Manitoulin Island, the Bruce Peninsula, Carden, Napanee, and Smith’s Falls (Figure 7). They also occur on smaller areas of near-to-surface limestone including the western Lake Erie islands, Flamborough Plain, local areas along the southern margin of the Precambrian Shield, and at a few sites along the Ottawa River.

The pre-European settlement extent of alvar vegetation is known for some areas within the Ontario portion of the Mixedwood Plains Ecozone+, including Manitoulin Island,55 the northern Bruce Peninsula,56 and the Carden57 and Flamborough58 limestone plains. Since European settlement, the areal extent of alvars has decreased on portions of Manitoulin Island. The south shore, from the middle of the island to the western tip, was originally described almost exclusively as open alvar. While numerous alvars are still present in this area, these systems are more isolated at present. Elsewhere on the island, some current alvars which were originally described as being forested, are apparently the product of forest fires.55 Many of the extensive alvars that originally occurred along the northern shore of Manitoulin have been degraded by grazing activities.59 Similarly, numerous areas of open alvar vegetation were noted by the original land survey in the upper Bruce Peninsula although fewer are present today.60

In contrast to Manitoulin Island and upper Bruce Peninsula, the areal extent of alvar in other regions may be unchanged or have increased since European settlement.60 Goodban58 found that existing alvars on the Flamborough Plain originally occurred in a landscape dominated by deciduous forest, with only a very few areas referred to as “broken land”. On the Carden Plain, numerous existing alvars were also noted by the original land surveyors, however, their extent and range has increased since European settlement. Logging and a subsequent conversion to ranch lands is responsible for the increase in areal extent of alvars in this area.57,61 While the extent of original alvar vegetation in eastern Ontario has not been estimated, many currently open (i.e., alvar) areas were mapped by original land surveyors as extensive areas of conifer forest. It is assumed that logging, slash burning, and conversion to pasture were factors in the creation of many of these open sites.60

There are at least 86 species of vascular plants known from alvars on the Ontario portion of the Mixedwood Plains, including seven endemic species. One of these, limestone hedge-hyssop (Gratiola quartermaniae), was only recently described62 as a scientific species from plant material collected in Ontario. Ten species are considered to be globally rare, and four others are nationally rare. Four provincially-rare moss species, and one lichen species, also occur on alvars.60 Specialized alvar habitats are important for at least 62 plant species -- 50% or more of their occurrences in the Mixedwood Plains Ecozone+ in alvars. Of these, 21 are mainly confined to alvars (86 to 100% of occurrences) and another 13 largely confined (71 to 85%) to them.63

Alvars also support a variety of rare and endangered animal species.45 One of Ontario’s most celebrated endangered species, the loggerhead shrike (Lanius ludovicianus), is found in alvars in the Mixedwood Plains. Alvar is important habitat for the blue racer (Coluber constrictor foxii), an endangered snake now known in Ontario only from Pelee Island. The endangered eastern foxsnake (Pantherophis gloydi) also inhabits alvar habitat on the island. On the Bruce Peninsula, the threatened eastern Massasauga (rattlesnake) (Sistrurus catenatus) is frequently found in alvars.60 Brownell (2000)60 also identified a number of terrestrial invertebrates, mainly butterflies, grasshoppers, tiger beetles, and, especially, mollusks associated with alvar habitat.

Alvars in Quebec

Small alvars, 21 in total, are known to exist in Quebec along the Ottawa River and in Montérégie and Lanaudière near Montréal, all located in the Mixedwood Plain Ecozone+. Covering a larger area historically, their total area is now 132 ha, with individual habitats varying in surface area from 1 to 27 ha.64

Alvars are known to harbor 66 provincially-listed species at risk in Quebec;64 for example, they are the only known habitats of the greater fringed gentian (Gentianopsis crinita). Of the alvars located in Quebec, those on Île-des-Cascades show the richest flora with 24 designated species.65 Alvars, as any other habitats, are exposed to perturbations from alien invasive species; the European buckthorn (Rhamnus cathartica) represents a threat for those rare habitats.64

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Key finding 3

National key finding
High loss of wetlands has occurred in southern Canada; loss and degradation continue due to a wide range of stressors. Some wetlands have been or are being restored.

Evidence from Ontario

Wetland extent in Ontario

It is estimated that there were 2,026,591 ha of wetland in the Ontario portion of the ecozone+ prior to European settlement, constituting 25% of the landscape.66 The highest concentrations of wetlands were found in southwestern and eastern Ontario. Essex County had the greatest wetland coverage in southwestern Ontario at 83%, followed by Kent and Lambton with wetland coverage of 56 and 50% respectively. In eastern Ontario, Prescott County had the greatest percentage of wetlands at 51% (Figure 8).66

Figure 8. Percentage of wetland cover in the Ontario portion of the ecozone+ prior to European settlement.
Southern Ontario Area
Long description for Figure 8

This map shows that, prior to European settlement, the majority of the Ontario portion of the ecozone+, from about 35 km east of Lake St. Clair to west of Ottawa, had from 5.1 to 20% wetland cover, interspersed with areas of 20.1 to 40% and a small number of areas with 40.1 to 60% wetland cover. One small area on the Niagara Peninsula had more than 60% wetland cover and a small area around Toronto is unassessed. Most of the western end of the ecozone+ had more than 60% of wetland cover, with a few areas between 20.1 and 60%. In the eastern end of the Ontario portion of the ecozone+, most of the area had from 40.1 to 60% wetland cover, with a few areas at 20.1 to 40%, and two small areas near the Quebec border with over 60% wetlands.

Note: Wetlands under 10 ha not included in analysis.
Source: Ducks Unlimited, 201066

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The extent of wetland in the Ontario portion of the ecozone+ has drastically declined with only 560,844 ha of pre-settlement wetland remaining by 2002 (Figure 9). This represents a loss of 72% of wetland area relative to pre-European settlement conditions and a reduction in total wetland coverage from 25 to 7%.66

Figure 9. Percentage of wetland cover in Ontario portion of the ecozone+ in 2002.
Southern Ontario Area
Long description for Figure 9

This map shows that, in 2002, most of the western part of the region had between 0 and 5% wetland cover, with increasing areas of 5.1 to 20% coverage to the east of Lake Huron and small pockets with 20.1 to 60% wetland cover. The central part of the region had mostly 5.1 to 20% coverage. East of the Ottawa River, wetland cover ranges from 0 to 20% with a number of areas with 20.1 to 60% cover.

Note: Wetlands smaller than 10 ha not included in analysis. Source: Ducks Unlimited, 201066 based on mapping from the Southern Ontario Land Resource Information System (SOLRIS).

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Recent trend information on wetland losses suggest that some of the losses have been recent. From 1982 to 2002, there was an average loss of 3,543 ha per year, or 0.17% per year.66 The greatest wetland losses have often occurred in areas which had the largest amounts of  pre-settlement wetlands (Figure 10). By 2002, Essex County, which had the highest pre-settlement percentage of wetlands (83%), had some of the lowest rates of coverage (0 to 5%). A similar situation was found in Prescott County which also had a high percentage of wetland cover historically but only had between 5 and 20% in 2002. The wetland trends presented only apply to large wetlands (&gt;10 ha) and are therefore a conservative estimate of wetland loss. If wetlands less than 10 ha in size had been included in these estimates, annual losses would be even higher.66

Figure 10. Percentage loss of wetlands in the Ontario portion of the ecozone+ between prior to European Settlement and 2002.
Southern Ontario Area
Long description for Figure 10

This map shows that the greatest percentage of wetland loss occurred in the western part of the ecozone+. The percentage of wetland loss was largest in the western and eastern regions, with loss percentages declining towards the central area. In the west, Essex, Kent, Lambton, Middlesex, Perth, Brant, Niagara and Toronto counties lost 85.1 to 100% of wetlands. To the east of Ottawa, Russell and Prescott counties also lost between 85.1 and 100% of their wetlands. In the west, Huron, Elgin, Oxford, Haldimand-Norfolk, Waterloo, Halton and Peel counties lost 65.1 to 85% of their wetlands, with the same percentages lost by Lennox and Addington, Frontenac, Ottawa-Carleton, Dundas and Glengarry counties in the east.  Losses of 45.1 to 65% of wetlands occurred in Bruce, Wellington, Hamilton-Wentworth, Dufferin, Simcoe and York counties in the west and Hastings, Leeds, Lanark and Stormont counties in the east. In the central area, Durham, Victoria, Peterborough and Northumberland counties lost between 35.1 and 45% of wetlands. Grey County in the west and Grenville County in the east also lost 35.1 to 45% of wetlands. Only Prince Edward County lost between 0 and 35% of wetlands.

Note: Wetlands smaller than 10 ha not included in analysis Source: Ducks Unlimited, 201066

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Data showing the rates of wetland loss over time from pre-settlement to the present are not available for most of the ecozone+, but a study was done along the Canadian shoreline of Lake Ontario.67 When mapping from as early as 1789 and up to 1962 was compared to mapping from 1977 and 1979, it was evident that wetland loss occurred along the Canadian shoreline throughout most of the 1800s, with the greatest loss occurring prior to 1950.67 The rate of loss was often greater in the 1900s than in the 1800s, potentially due to improvements in drainage technology over time. The first reference to subsurface drains in Ontario is in 1844.68 The rate of land drainage was at its maximum between 1967 and 1977 when new drainage technologies (plastic drainage tubing and machinery able to lay 30 m of drain per minute) were introduced.68 Great Lakes coastal wetlands (see next section) were not included in the analysis presented above.

In 2009, percent cover of the different wetland types found in the Ontario portion of the ecozone+ varied greatly by physiographic zone. Swamp was the most abundant wetland type in all zones, ranging from 65.2% of the total wetland area in the Frontenac Arch to 89.4% of the wetlands in the Southwest physiographic zone (Table 3).4

Table 3. Composition of total wetland cover (based on area) across four wetland types  in the Ontario portion of the ecozone+ by physiographic zone, 2009.
Physiographic areaPercent bogPercent fenPercent marshPercent swampPercent open wetland (bog, fen, marsh)
Frontenac Arch0.20.234.465.235

Southern Ontario Area

In 2009, most of the Ontario portion of the ecozone+had less than 50% of its remaining wetlands in patches over 200 ha (Table 4 ). When looked at as a percentage of the physiographic areas as a whole, cover of wetlands over 200 ha was lowest (2%) in the Southwest and Escarpment, and highest (10%) in the Eastern Physiographic zone.4

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Table 4. Percentage wetland patches in Ontario portion of ecozone+ by physiographic zone, 2009.
Physiographic areaPercentage of wetland patches larger than 200 haPercentage of wetland patches over 200 ha which are open wetlandPercentage of wetland patches over 200 ha which are swampPercentage of physiographic area which has wetlands 200 ha or largerAverage wetland patch size for patches 200 ha or greater
Central 4316847648
Frontenac Arch2245553729

Note: Wetland includes bog, fen, marsh, and swamp while open wetland does not include swamp.
Source: Ontario Ministry of Natural Resources, 200970 and Taylor et al., 20124

Great Lakes coastal wetlands

Located mainly along the shores of the southern Great Lakes (Ontario, Huron, and Erie) and their connecting channels (the St. Clair, Niagara, Detroit and St. Lawrence rivers, and Lake St. Clair), the Great Lakes coastal wetlands currently encompass over 70,000 ha.71 These wetlands provide continentally significant habitat for many migratory waterfowl,72,73 breeding and non-breeding habitat for many species, including globally rare species and species at risk,74,75 important spawning habitat for many fish, and a diversity of plants. They are considered vital to the health of the Great Lakes.76

Despite their ecological value, the loss of Great Lakes coastal wetlands has been severe. McCullough69 estimated that, by 1984, about 35% of the coastal wetlands along the Canadian shorelines of lakes St. Clair, Erie, and Ontario had been lost. Whillans67 provides evidence that 43% (1,920 ha) of historical coastal wetlands along the Canadian shore of Lake Ontario west of the Bay of Quinte were drained or destroyed between 1789 and 1979, with the greatest loss occurring between Toronto and the Niagara River where 73 to 100% of original coastal wetlands have been lost.67 Most of these losses occurred between the late 19th and early 20th centuries, when large wetlands were filled or dredged for shipping, industrial, and urban development purposes.77 Today, many of the remaining coastal wetlands continue to be degraded by factors such as water level regulation, sedimentation, contaminant and nutrient inputs, climate change, invasion of non-native species, and intensive industrial, agricultural, and residential development.77 Water level regulation in Lake Ontario, for example, is a major stressor to coastal wetlands and their inhabitants,78 while along Lake Erie, sedimentation, nutrient loading, and contaminants are major wetland stressors.77

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Evidence from Quebec

Wetland extent in Quebec

In 2009, the total area of wetlands in the Mixedwood Plains Ecozone+ in Quebec was approximately 2,820 km2, or 9% of the Quebec portion of the ecozone+ (31,925 km2).80

Grenier and Allard (2012)80 assessed the status of wetlands in the Quebec portion of the ecozone+based on a compilation of existing wetland mapping for the region. Data consisted of seven different datasets from various projects derived either from satellite imagery (e.g., Landsat, Radarsat) or orthophotos from the early 1990s to 2009. Wetlands were divided into five categories: bog; fen; swamp; marsh; and shallow water (aquatic grass bed). Table 5 and Figure 11 present the breakdown and distribution by different categories of wetland.

Table 5. Area per category of wetland in the Quebec portion of the Mixedwood Plains Ecozone+, 2009.
Wetland CategoryArea of the territory that is wetland
Breakdown by wetland category
Proportion of the territory that is wetland (%)
Bog 839302.6
Flooded forest549191.7
Shallow water334121.0

Source: Grenier and Allard, 201280

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Figure 11. Distribution and classification of wetlands in the Quebec portion of the Mixedwood Plains
Montreal Area
Long description for Figure 11

This map and pie chart shows the percentage and distribution of six classifications of wetlands.
The pie chart shows the that the region had 30% ombrotrophic peatland (bog), 2% menerotrophic peatland (fen), 15% marsh, 19% swamp, 12% shallow water and 22% partially classified.
The map shows that ombrotrophic peatland (bog) is mainly found on both sides of the St Lawrence River in the area between Lac Saint-Pierre and Quebec City. The largest area of menerotropic peatland (fen) is located on the north side of the river to the west of Lac Saint-Pierre. Marsh is primarily located on the north and south shores of Lac Saint-Pierre, with smaller areas in the western tip of the region and on an island east of Quebec City. Swampland is found primarily around Lake Saint-Pierre and in the area south of the river between Lac Saint-Pierre and Quebec City. Shallow water is found on the south shore of Lac Saint-Pierre and the south side of the mouth of the St. Lawrence River. Partially classified wetlands are scattered along the region south of the river.

Source: Grenier and Allard, 201280

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Bogs are spread out but occupy large areas, for a total of 839 km2.80 The Lac-à-la-Tortue bog (6,800 ha) south of Shawinigan, of which 8% is a designated "ecological reserve," and the Grande Plée Bleue bog (1,500 ha), south of Lévis, are examples of natural bogs that have remained relatively untouched by human activity. In terms of biodiversity, a few large fen complexes also exist near Villeroy and Lyster, southwest of Lévis. In Centre-du-Québec, where 80% of Quebec’s cranberry farms are located, cranberry farming is responsible for the loss of large areas of bog.81

Fens are mostly found south of Montreal in the region of Napierville, Saint-Clotilde, and around Missisquoi Bay.82 These fens are highly exploited and have lost their original structure. "Ecological reserve" status ensures the strict conservation of part of the Lanoraie marshlands, which extend over 5,500 ha and are surrounded by farmland. Fens are the category of wetland that is least present in the territory, with an area of 64 km2.80 Marshes cover an area of 411 km2, or 1.3% of the Quebec portion of the ecozone+.80 The largest marsh areas are found near Lake Saint-Pierre; however, they also can be found along the St. Lawrence River, around different islands, at the mouths of rivers, and in the bays of the main watercourses.83

The area covered by swamps is 549 km2, or 1.7%, of the Quebec portion of the ecozone+.80 Most of the swamps are found in the floodplain of Lake Saint-Pierre, but the Richelieu and Ottawa rivers are home to large areas of swampland as well. The periods of flooding for this type of wetland on the edge of terrestrial habitats can vary greatly from one year to the next. For example, along the St. Lawrence River, swamp areas where silver maple trees (Acer saccharinum) grow were flooded an average of 31 days per year between 1972 and 1976, but only 12 days per year between 1980 and 1984.

Shallow water (aquatic grass bed) covers 334 km2, or 1% of the Quebec portion of the ecozone+.80 Most of the shallow waters in the ecozone+are located at Lake Saint-Pierre, where the water has gone down over many years, thus favouring the development of submerged and floating aquatic plants at the edges of the marshes. The mud flats in the region of Île d'Orléans are also included in this category along with many transition areas between the deep water and the marshes along rivers.

Urban development, agriculture, navigation, resorts, and poor land-use planning are all pressures that have had significant cumulative, and often permanent, impacts on wetlands in the Quebec portion of the ecozone+.81 While it is well-known that the losses recorded since European settlement are enormous, they are very difficult to assess because of the type of data that is available. Based on an analysis comparing the current wetlands area in the St. Lawrence Lowlands to a map of historical wetlands made based on types of soil, 80% of bogs have been lost due to human activity.80 Similar losses (69 to 83%) were recorded for the territories surrounding the metropolitan areas of Montréal and Ottawa–Gatineau during the period from 1800 to 1981. Wetland drainage for agricultural purposes has been and remains the main threat to wetlands and is responsible for 85% of total losses; urban and industrial expansion accounts for 9% of all losses. Although it was not possible to precisely determine changes from two maps with different scales and created using very distinct methods of identifying wetlands, a visual comparison of the maps suggests that bog areas have been reduced by 50% since colonization.

The regions most affected are urban areas and the Montérégie region. Strong pressures observed between 1993 and 2001 in the farmscape towards intensifying annual crop production at the expense of forage crops and pastures and the loss of woodlands to housing developments and agriculture suggest that the wetlands present in this territory have been greatly affected.

Between Montréal and Lake Saint-Pierre, and specifically in the Lake Saint-Louis/Boucherville area, swamps have practically disappeared since this is the driest type of habitat and thus is the first to succumb to the pressures of urban expansion. Some islands in the St. Lawrence River have been spared, such as the Dowker Island, Iles-aux-Herons, and Iles-des-Soeurs, as well as the islands in the Sorel-Tracy archipelago. Swamps in the latter area have been subject to stress, principally because of agricultural activities. Dowker Island is one of the most beautiful examples of swampland in the entire territory. More specific analyses of changes were performed for the metropolitan communities of Montréal and Quebec City, as well as for the Montérégie region. Since the 1990s, metropolitan Montréal and Quebec City have lost 6 and 7% of their wetlands respectively.80 Between 1964 and 2006, the Montérégie region lost 2,800 ha, or 22%, of wetland of the area they occupied in 1964 (Table 6).80 It should be noted that agricultural development and forest regrowth are responsible for 70 and 11% of wetland loss, respectively. The latter display a gradient of fragmentation similar to that of forests, a number that becomes greater as you move from west to east and reflects the amount of land used for agricultural purposes and urban expansion. In the Montérégie region, the average wetland area is 4 ha, with 86% of these wetlands under 5 ha. In the rest of the ecozone+, average wetland area is 8 ha, with 84% of wetlands under 5 ha.80

Table 6. Distribution of wetland losses based on how the land was allocated in the Montérégie administrative region, 1964-2006.
AllocationArea (ha)Proportion lost (%)

Source: Grenier and Allard, 201280

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While an evaluation of wetland losses is not available for the rest of the ecozone+ due to a lack of reliable data, it is reasonable to believe that the rates of wetland disappearance for the whole ecozone+ are likely equivalent, or slightly below, the rates observed in Montérégie.

Tidal marshes

Both freshwater and saltwater tidal marshes are found in the Quebec portion of the ecozone+. The freshwater tidal marshes, which are almost continuous for 200 km (mostly along the south shore of St. Lawrence River) upstream and downstream of Quebec City, are the largest and some of the least polluted in North America and a very rare habitat worldwide.136

Over 60 km2 of riparian habitat along the St. Lawrence River was modified from 1945 to 1984.84 Most changes occurred prior to the mid-1970s and were a result of draining and filling of open waters and wetlands for housing, roads, and agriculture. Some 360 ha were backfilled in favour of industrial development in the upstream section of the estuary, while harbour development and highway construction brought about the loss of 270 ha around Quebec City. At the downstream end of the estuary, more than 500 ha were lost to maritime facilities and agricultural activities.138 Losses near major urban centres were the greatest;84,85 for example, 83% of Montréal’s wetlands were lost by 1976.86 Construction of water control structures, including dams and the St. Lawrence Seaway (1954 to 1958), was also responsible for change in the late 1950s,85 while urbanization was more important after that time.86

Since the 1970s, the overall extent of wetlands has increased, although there is variability depending upon the type and location of the wetland (Figure 12).84 While wetland loss continues due to urbanization (Montréal area) and agriculture (Lake Saint-Pierre), restoration efforts and reduced water levels have resulted in a 2.7% (603 ha) net gain of marshes and swamps between 1990 and 2002.84 Gains were mainly in the fluvial and upper estuaries and occurred mainly at the expense of open water. Declining water levels in the 1990s may have accelerated the drying trend in some areas,84,87 transforming low marshes to high marshes and swamps.

Figure 12. Percent change of wetland area by physiographic unit along the St. Lawrence River. A) Change from 1945 to 1978, B) Change from 1970–1978 to 2001–2002
images of Quebec City Area
Long description for Figure 12

This figure comprises two maps showing wetland change in the periods from 1945 to 1978 (map a) and from 1970-1978 to 2001-2002 (map b). The physiographic units identified are the Fluvial estuary, stretching from the eastern tip of Lac Saint-Pierre to the eastern end of Ile d’Orléans; the Upper estuary, from the eastern tip of Ile d’Orléans to the mouth of the Saguenay River; and the Lower estuary, eastward from the mouth of the Saguenay River.

Map (a) shows that, in this period, wetland loss of 1 to 6% occurred on both sides of the river from Cornwall to east of Montreal and along Lac Saint-Pierre, on the north bank from the midpoint of the Fluvial estuary to just east of Quebec City, and on the south bank from east of Quebec City to the end of the Fluvial estuary, and the along the length of the Lower estuary. Wetland loss of 7 to 17% occurred on both sides of the river from east of Montreal to the western tip of Lac Saint-Pierre and for a short distance eastward from the eastern tip of Lake Saint-Pierre, and on the south bank in the eastern half of the Upper estuary. Wetland loss of 29% occurred on the north bank in a small area extending east and west of Quebec City. Map (b) shows that the percentage of wetland area in this period remained stable on both banks from Cornwall to east of Montreal and from Quebec City to the eastern edge of the Fluvial estuary. Wetland gains of, from west to east, 6.2%, 6.5% and 8.6% occurred on both banks west of Montreal and from a short distance east of Montreal to the western tip of Lac Saint-Pierre. Both banks of the river from the eastern tip of Lac Saint-Pierre to Quebec City had wetland gains of 17.4%, and the south bank had gains of 4.7% and 11.9% through the Upper and Lower estuaries. Wetland losses occurred on both river banks for a short distance east of Montreal (17.1%) and along Lac Saint-Pierre (0.5%).

Source: (a) adapted from Lehoux and Chamard, 2002;85 (b) adapted from Jean and Létourneau, 200790

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Considering the highly dynamic and harsh environmental conditions (e.g., strong tides, currents and waves, ice scouring) in the estuary, large variations in wetland surface area are to be expected from year to year, hence the importance to focus on permanent losses due to human activities. Some 27 ha of low marshes dominated by smooth (saltmarsh) cordgrass (Spartina alterniflora) have been lost to shore erosion and agriculture in the Kamouraska region.

Harsh tidal conditions (twice-daily tides as high as 6 m) have resulted in many specialized species, some of which are endemic species at risk such as the Victorin’s gentian (Gentianopsis virgata ssp. victorinii) and the Victorin’s water-hemlock (Cicuta maculata var. victorinii), while others such as the rare Parker’s pipewort (Eriocaulon parkeri)and eastern wild rice (Zizania aquatica var. brevis)are found in other estuaries of the east coast

The marshes become progressively more brackish downstream of the eastern point of Île d'Orléans (Orleans Island) until they eventually become true salt marshes, just east of Kamouraska at the extreme eastern tip of the ecozone+. These salt marshes are very rich and also are characterized by a unique assemblage of temperate, boreal, and even arctic species. American cordgrass species (Spartina alterniflora, S. patens, and S. pectinata) cohabit with circumpolar arctic species like Hoppner’s sedge (Carex subspathacea), and boreal amphi-Atlantic (found on both sides of the Atlantic Ocean) species like chaffy sedge (C. paleacea), estuary sedge (C. recta), saltmarsh sedge (C. salina), and estuarine sedge (C. vacillans).136

In 2000/01, exotic invasive plants comprised 14% of vascular plants in St. Lawrence River wetlands.88 Their expansion can be attributed to shoreline alteration, excavation of the navigation channel, and water level regulation, which have reduced the magnitude of water level variation, decreased hydrodynamics in shallow littoral areas, and reduced the efficiency of the river to flush nutrients from sediments and to uproot emergent vegetation.89

Although the number of exotic species is fairly stable along the St. Lawrence, their coverage varies, from 44 % in the Montréal sector to 6 to 10% in the fluvial and upper estuaries.88 Flowering rush (Butomus umbellatus) is by far the most common invasive species in the marshes along with purple loosestrife (Lythrum salicaria), but the impact may not be as large as other invaders, such as common reed (Phragmites australis). For example, common reed can be considered rare but its cover is greater than 50% in 71% of the sites where it is found. In contrast, purple loosestrife may reach such coverage in only 9% of the numerous sites where it is found in the St. Lawrence marshlands.88

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Key finding 4
Lakes and rivers

National key finding
Trends over the past 40 years influencing biodiversity in lakes and rivers include seasonal changes in magnitude of stream flows, increases in river and lake temperatures, decreases in lake levels, and habitat loss and fragmentation.

The Mixedwood Plains Ecozone+ includes portions of the St. Lawrence and Ottawa rivers plus several other large rivers and their watersheds, but excludes the waters of the Laurentian Great Lakes. Hundreds of lakes and thousands of kilometres of rivers make up approximately 3% of the total surface area of the Mixedwood Plains Ecozone+.91 The Mixedwood Plains is a human-dominated, heavily fragmented landscape. While agriculture dominates much of the land use in the ecozone+, the area is strongly affected by urban growth with several large cities and extensive urban land cover.92,93 The combination of sedimentation and organic pollution from intensive agricultural operations,94,95 fragmentation from dams,96,97 introductions of aquatic invasive species,98,99 and increasingly high proportions of impervious surfaces in urban areas100 have contributed to highly stressed freshwater ecosystems.


An analysis of changes in streamflow in rivers with minimal flow control or impact upstream was carried out for ESTR,100 updating results published in 2000 comparing 1976 to 1985 with 1986 to 1995.102 To facilitate the analysis of trends nationally, sites were organized into six groups with similar intra-seasonal patterns of flow (hydrology groups).

Between the periods 1961 to 1982 and 1983 to 2003, most streams in the Mixedwood Plains demonstrated a unique pattern for Canada showing an increased discharge throughout all seasons, except spring. During months with increased flows, there was an average 50% increase in discharge relative to the median for most stations. The majority of streamflows in the ecozone+ are driven by mixed rain and snow processes, with highest runoff occurring in the spring followed by low summer flows and then higher flows again in the fall. Snowmelt early in the year causes the spring peak while the higher fall flows are rain-induced.101 Climate variables associated with this group of streams exhibited warmer temperatures throughout most of the year, with wetter summers and falls. Figure 13 shows the location of the hydrometric stations used in the analysis and presents the change in streamflow between the time periods for the Nith River which exhibits change typical for this group of streams. It also shows the change in temperature and precipitation. Because this analysis was based on reference sites in streams and watersheds with little human alteration, observed changes through time are likely related to trends in temperature and precipitation.

Figure 13. Changes in streamflow, temperature, and precipitation between 1961–1982 and 1983–2003 for the Nith River in the Mixedwood Plains Ecozone+. Hydrology groups represent clusters of rivers showing similar hydrologic responses to variations in climate. For information on the specific hydrology groups mentioned above, see Cannon et al. 2011.101 a) shows locations and hydrology groups of stations in the Mixedwood Plains, including the Nith River; b) shows streamflow change in Nith River, representative of Hydrology Group 2a; c) shows changes in temperature for the Nith River; and d) shows changes in precipitation for the Nith River.
Four graphs
Long description for Figure 13

This figure contains a map and three line graphs. The map (a) shows the location of hydrometric stations in the ecozone+. Of the 13 stations in hydrology group 2a, 4 are ranged around the western part of Lake Ontario from Toronto to Niagara Falls, 3 are in the area of London, 3 are along Georgian Bay, and 3 are along the St. Lawrence River from south of Ottawa to Quebec City. One station in hydrology group 2d is located between London and Lake St. Clair, and one station in group 4a is located at Toronto. An arrow points to the location of the Nith River, west of Lake Ontario.

The line graphs show changes for the Nith River in streamflow (b), temperature (c) and precipitation (d) between 1961-1982 and 1983-2003.  The graphs show monthly mean measurements from January to December. Graph (b) shows that streamflow in the two periods followed a similar pattern, reaching the highest level in March/April at over 20 m3/s, and dipping to its lowest level in July/August. Overall, streamflow levels in the earlier period were lower for most of the year than those for the later period. Graph (c) shows that the temperature curve was almost identical for both periods, with the earlier period showing slightly lower temperatures from January to March. Lowest temperatures were reached in January (1961-1982: -90C; 1983-2003: -60C), and highest in July/August (190C). Graph (c) shows that the greatest variation between the two periods occurred in precipitation amounts. While precipitation amounts in 1961-1982 fluctuated regularly throughout the year between 60 and 85mm, in 1983-2003 precipitation declined from about 75mm in January to below 60mm in March and then climbed steadily to 85mm in May. While some fluctuation in amounts occurred throughout the rest of the year, precipitation amounts in the later period did not fall below 75mm and rose to a high of almost 95mm in November.

Source: Cannon et al., 2011101

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Although there has been no comprehensive analysis on trends in hydrology of human-impacted streams across the ecozone+, the hydrology of most major river systems in the Mixedwood Plains has been altered by common stresses such as riparian zone destruction, barriers (dams), drainage, and channelization, all the result of agricultural development and urbanization of watersheds.103,104,105 Evidence from the Ontario portion of the ecozone+ has shown that reforestation since the 1950s has resulted in improved base flows, reduced peak flows, and stability of channel form for some river systems (e.g., Buttle 1994106 and 1995107).

Water temperatures

Morris and Corkum (1996)108 have shown that loss of riparian cover on streams in agricultural areas of the Ontario portion of the Mixedwood Plains resulted in increased mean monthly water temperatures, increased daily temperature fluctuations, and increased nutrient inputs. Increased water temperatures, due to on-line ponds and deforestation, are also a major stress on the cold-water streams draining into Lake Ontario105 and in many other watersheds  (e.g., GRFMPIC, 2005103 ; OMNR and TRCA, 2005104). Despite recent improvements in riparian condition in some watersheds, undisturbed reaches with more pristine habitat conditions tend to be restricted to headwater areas. Historically, many of these cold-water habitats extended substantially further down the watershed.105 In contrast, some river systems have had reservoirs with hypolimnetic releases, artificially cooling downstream reaches and altering the fish and benthic community (e.g., Bellwood Reservoir, Grand River).109,110

Over the past 30 to 40 years, increased water temperatures have been observed for lakes of the Mixedwood Plains (e.g., Robillard and Fox, 2006111). This warming trend has also been demonstrated with longer ice-free seasons and earlier spring breakup dates for lakes during a similar period.112

Water levels

Historic canal construction (e.g., Rideau Canal, Trent–Severn Waterway) has altered water levels and trophic status in many large rivers and lakes of the Mixedwood Plains.113,114 For example, water level in Upper Rideau Lake was raised 1.5 m during canal construction.113 Both cold- and warm-water streams have undergone fragmentation, habitat alteration, declines in water quality, and altered water levels due to water control structures, small relic milldams, and recreational on-stream ponds.103,104 Such barriers are extensive throughout the ecozone+. The natural flow regimes of the Ottawa and St. Lawrence rivers have also been greatly altered through the construction of dams for water level regulation and power generation over the past 130 years.96,115 In a global study, Nilsson et al.116 found that large river systems across the Mixedwood Plains (and elsewhere) are strongly affected by dam-caused river fragmentation and flow regulation.

Aquatic biodiversity

The Mixedwood Plains Ecozone+ supports the highest freshwater fish biodiversity in Canada,117 representing 97% of the total number of taxa for Ontario, 86% of the total for Quebec, and 78% of the total for Canada. The ecozone+ also has the most diverse freshwater mussel fauna in Canada (41 species of out of total of 55 species in Canada).118

Fish and other aquatic communities are changing in response to changes in aquatic habitats throughout the ecozone+. Major stressors include eutrophication of cold-water lakes, changes in the productivity of warm-water lake habitats (see Nutrient loading and algal blooms), altered flows, habitat fragmentation, siltation and nutrient enrichment, contaminants, and impoundments in rivers and streams.103,115,119,120

A typical pattern of fish community change in flowing systems of the Mixedwood Plains has been a contraction of cold-water species ranges toward the headwaters while warm-water species have expanded their ranges upstream in the systems (e.g., Mahon et al.121). Brook trout (Salvelinus fontinalis) was historically the top predator in many shallow headwater lake/cold-water stream systems and are now largely restricted to headwater areas.104,122,123,124,125,126 In addition to having more suitable cold-water habitats, these headwater areas are largely isolated from introduced migratory salmonines (e.g., Atlantic salmon Salmo salar, brown trout Salmo trutta).

Patterns of fish species dominance in lakes in the ecozone+ have also changed from historical distributions in response to stressors such as unauthorized and unintentional introductions (e.g., rock bass Ambloplites rupestris, zebra mussels Dreissena polymorpha, round gobies   Neogobius melanostomus) and movements between once isolated watersheds.105 For example, native fish communities of the Crowe River watershed differed from those of the Kawartha Lakes prior to the building of the Trent–Severn Waterway, but a change in water levels allowed movement of fish between these two systems and homogenized the fish communities over the last 150 years. Lakes in close proximity to these, but not connected to the Waterway (e.g., Dalrymple and Head lakes) still maintain fish community differences.105

Freshwater biodiversity is at greatest risk throughout the more human-dominated watersheds of the ecozone+, reflecting degraded habitat and water quality. Loss of riparian areas, disconnection of rivers from their floodplains, habitat fragmentation, and increased urban and agricultural development within watersheds have contributed significantly to loss of freshwater biodiversity.127,128,129,130

Of the 131 fish taxa native to the ecozone+, 36 are of conservation concern, which is more than any other vertebrate group within the ecozone+.131 Several recovery strategies are being implemented that aim to rehabilitate the aquatic habitats upon which these species depend.

Metcalfe-Smith et al.(1998)132 documented a reduction in freshwater mussel diversity and a shift in community dominance over the last 140 years. A number of studies have documented population declines and a reduction in the ranges of species.120,133,134 Of the 41 species of freshwater mussels found in the Mixedwood Plains, 10 species have been assessed as Endangered and one species as Special Concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

A number of efforts are underway to assist in the recovery of freshwater mussels in the Mixedwood Plains. Ecosystem-based recovery strategies have been developed for a number of systems. Metcalfe-Smith et al.(2000)135 found that mussel populations in the Grand River had recovered from historic lows in the 1970s. The number of species throughout the system increased from 17 to 25 between the early 1970s and the late 1990s, while in the lower reaches of the mainstem, the number of species increased from 6 to 21. The increased number of species in the system was attributed to improved water quality over the past two to three decades.

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Key finding 5

National key finding
Coastal ecosystems, such as estuaries, salt marshes, and mud flats, are believed to be healthy in less developed coastal areas, although there are exceptions. In developed areas, extent and quality of coastal ecosystems are declining as a result of habitat modification, erosion, and sea-level rise.

Tidal marshes are presented under the Wetlands key finding.

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Key finding 7
Ice across biomes

National key finding
Declining extent and thickness of sea ice, warming and thawing of permafrost, accelerating loss of glacier mass, and shortening of lake-ice seasons are detected across Canada’s biomes. Impacts, apparent now in some areas and likely to spread, include effects on species and food webs.

Evidence from Ontario – lake and river ice

The formation and break-up of ice are important seasonal events in mid- to high-altitude lakes and rivers.139 Changes in the timing of these events can have important impacts on aquatic communities. Ice cover limits the amount of the sun’s energy that enters the water, decreases the amount of evaporation, and decreases the amount of time in which lakes and rivers are a source of greenhouse gases.140 Ice cover affects both the flora and fauna within aquatic ecosystems.141 The effects of ice also reach beyond the water’s edge as ice scouring of shorelines impacts the species living in riparian areas, while the flooding caused by ice jams as well as normal spring flooding as ice and snow are melting have a great impact on soils and thus the species living in flood plains and riparian areas.142 Generally, smaller lakes freeze earlier than large ones and deeper lakes freeze later than shallow lakes (due to the specific heat of water). Lakes that are able to warm more in the ice free season (clear lakes) will freeze later than lakes with cooler temperatures. Lakes further down a watershed often break up earlier than headwater lakes, perhaps due to increased flow from snowmelt higher in the catchment.112

The earliest data on ice break-up within the Mixedwood Plains Ecozone+ comes from Toronto Harbour, where data collection began in 1822143, and Lake Simcoe, where data collection began in 1853.112  When the data from Lake Simcoe was divided into time periods, it was found that the time period associated with the end of the Little Ice Age (1853–1899) showed a statistically significant trend indicative of warming temperature in both ice break-up and length of the ice free season. The period from 1950 to 1995 also showed evidence of warming temperatures, while the time period between 1900 and 1949 showed a cooling trend.112 When the entire time period was examined together (1853 to 2001) for the 46 lakes studied in southern Ontario, a significant trend towards earlier break-up dates and longer ice-free seasons was observed.112 When the average rates of change in freezing and break-up were compared between the more recent period of rapid climate warming (1975 to 2004) and historical rates observed within the northern hemisphere, it was found that in the Great Lakes region of both Canada and the United States, freeze-up was occurring 3.3 days later per decade and break-up 2.1 days earlier per decade, while the average ice duration decreased by 5.3 days per decade.139

The annual cycle of ice formation and loss on the Great Lakes affects physical processes within the lakes and in the adjacent atmospheric boundary layer, which in turn affect both the economy and the ecology of the Great Lakes region141 within the Mixedwood Plains. When the severity of ice cycles on the Great Lakes was examined for 1973 to 2002, it was found that about half of the mild ice cycles (late first ice, early last ice, and shorter ice duration) occurred in the last five years of the 30-year study period (1998 to 2002) while over half of the severe ice cycles occurred in the first 10 years of the study period (1977 to 1982).141

Percentage cover of ice on the Great Lakes decreased between 1973 and 2008 (Figure 14).142 Since 1970, there has been a decline of about 40% in ice cover on lakes Michigan and Ontario, while ice cover on Lake Superior decreased by about 35%, on Lake Erie by 19%, and on Lake Huron by 18% (Table 7). Seasonal average ice cover is usually greater on Lake Superior (due to its cooler more northerly location), Erie, and Huron (due to shallower depths) than on lakes Michigan and Ontario (which though more southerly than Superior are relatively deep).

Figure 14. Changes in seasonal percentage maximum ice cover on the Great Lakes, 1973–2008.
bar chart
Long description for Figure 14

This bar and line graph shows the seasonal percentage of maximum ice cover for each year from 1972 to 2008 and the general trend in maximum ice cover percentage over the period. Lowest ice cover percentages occurred in 1975, 1982, 1986, 1994, 1997-2001 and 2005, when maximum ice cover was below 40%. Highest ice cover percentages occurred in 1976-1978, 1980, 1981, 1984, 1985, 1993, 1995 and 2002, when maximum ice cover was above 70%. The line graph shows an overall downward trend in maximum ice cover from just below 70% in 1972 to 40% in 2007.

Source: Karl et al., 2009;144 updated from Assel et al., 2003145 using data from the National Oceanic and Atmospheric Administration

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Table 7. Mean maximum ice coverage (in %) on the Great Lakes by decade, 1970s to 2000s.
Lake1970–19791980–19891990–19992000–2008% change (1970–2008)

Source: Ontario Biodiversity Council, 2010146 – updated from SOLEC, 2009,147 using data from the Canadian Ice Service Seasonal Summaries for the Great Lakes (2000–2008)148

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The changes in ice cover since the 1970s may be connected to changes in the large-scale atmospheric and oceanic oscillations that influence the climate of the Mixedwood Plains. Links have been made between changes in the ENSO (El Niño/southern Oscillation) and changes in winter temperatures.149 When Great Lakes ice records were examined between 1963 and 1990,150 a relatively strong tendency for below average ice cover (46% of the lowest annual maximum ice) was found associated with warm El Niño winters. Since the mid-1970s, there has be a shift toward more prolonged and intense El Niño episodes.149

The breeding success of many cold-water fish species is directly linked to the thermal conditions of the water body they live in. When studied in semi-controlled and laboratory conditions, breeding success of lake whitefish (Coregonus clupeaformis), a cold-water fish, was found to be inversely related to thermal conditions.151 Also, water temperatures directly determine when and how much ice forms. In a field study, the late falls and winters of 2003/04 and 2004/05 were cold with extensive ice cover in eastern Lake Ontario.152 Those spawning seasons were followed by abundant lake whitefish larvae in Chaumont Bay in 2004/05. In contrast, the winters of 2005/06 and 2006/07 were mild and with relatively little ice cover and the subsequent lake whitefish larval populations were low.152 The breeding success of lake trout (Salvelinus namaycush) is similarly impacted. When lake trout hatchling survival was examined in association with water temperature and time of hatch, warmer temperatures were associated with pre-mature hatch, early yolk absorption, and death while colder water temperatures were associated with slow development, later hatch, and high survivorship (Figure 15).153  Loss of ice cover appears to be indicative of negative effects on these and other cold-water species.

Figure 15. Mean daily water temperatures associated with lake trout spawning at Yorkshire Bar, eastern Lake Ontario, 1989–1993.
graph image
Long description for Figure 15

This line graph shows the spawning rate and pre-swim-up live fry survival percentages of lake trout between October 1st and April 30th. The earliest, highest temperature (19 October) was 12.7 0C, the mean temperature (29 October) was 11.5 0C, the later, lower temperature (7 November) was 9.5 0C, and the latest, lowest temperature (13 November) was 8.8 0C. The curves illustrating the cumulative thermal units (degree-days) all show a steep increase from their start dates to early January, then level off until the beginning of April, when they begin to increase again. The CTUs recorded on May 1st are approximately 675 (beginning 19 October), 550 (beginning 29 October), 475 (beginning 7 November), and 400 (beginning 13 November). The extrapolated May 1st percent of survival to the pre-swim-up stage is 0% for 19 October, 10% for 29 October, 19% for 7 November and 21% for 13 November. The spawning rate was at its highest in mid-October, declined steadily to early January, then leveled off until the beginning of April, when it began to increase again.

The mean daily water temperatures were taken at the surface of the boulder-cobble substrate (4.5 m) where the incubators were located on Yorkshire Bar from the beginning of the spawning period to the end of April the following spring. The months are delineated by long, dark ticks; shorter, lighter ticks mark 7-day intervals. Includes the beginning and end of the in situ incubation period. Mean daily water temperatures associated with the lake trout spawning period in eastern Lake Ontario are delineated by vertical solid lines falling on the appropriate dates: earliest, highest temperature; mean; later, lower temperature – 9.5°C; latest, lowest temperature. The dates when these temperatures are reached mark potentially important times when incubation would begin for naturally deposited and fertilized lake trout eggs in eastern Lake Ontario. Curves (dashes) illustrate the cumulative thermal units commencing on the respective dates (19 October, 29 October, 7 November, and 13 November). Percent survival to the pre-swim-up stage, extrapolated from these dates to 1 May (vertical dotted line), is also shown. Source: Casselman, 1995153

Warmer temperatures create thin nearshore ice cover which is easily broken up and pushed by offshore winds resulting in ice piling and loss of habitat for invertebrate species.154 Such an occurrence is reported for Lake Ontario where in March of 1986, ice on Lake Ontario at Kingston weakened in rapidly warming air temperatures (17°C) and offshore winds combined to created ice piling along the shoreline to a height of 2.5 m. Stones from the shoreline weighing up to 206 kg were moved to the top of the ice pile.155 A study of invertebrate habitat use in   Lake Huron coastal wetlands showed that nearshore invertebrate community structure differed between areas experiencing wave exposure and those in protected locations.156

The amount of ice free area on the Great Lakes has a large impact on the amount of “lake effect” snow experienced in the snow belts around the Great Lakes. In a study of snowfall data from 1925 to 2007 for the Great Lakes area, an upward trend in snowfall was found in both the Superior and Michigan snowbelt areas.157 There were also upward trends in air temperature for Lakes Superior and Michigan which suggest that warmer surface waters and decreased ice cover are contributing to the upward snowfall trends by enhancing lake heat and moisture fluxes during cold air outbreaks.157

One of a few positive changes that may occur due to decreased ice cover on lakes is a decrease in winterkill (death of fish due to oxygen depletion under ice). When the impacts of decreased ice cover on eutrophic lakes less than 40 m deep were modeled for the northern United States (adjacent to the Mixedwood Plains), based on a 2 X CO2 scenario, winterkill was projected to disappear from all these lakes as under-ice dissolved oxygen levels will no longer reach anoxic conditions.158

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Ecozone+-specific key finding

Coastal dunes on the Great Lakes

Freshwater coastal dunes are open sand ecosystems located predominantly along the shorelines of the Great Lakes (Figure 16). They are considered to be among some of the most fragile ecosystems found in North America.159 They include both areas of exposed sand as well as areas stabilized by grasses, herbs, and shrubs. Trees may occur as scattered individuals or as small patches. As coastal dunes are narrow, linear features restricted to major lake and river shorelines, their total area in the Mixedwood Plains is quite small. Major dune systems are found on the Canadian Great Lakes at Sauble Beach, Carter Bay, Pinery Provincial Park, Great Duck Island, and Wasaga Beach on Lake Huron, Point Pelee National Park, Long Point, and Point Abino on Lake Erie, and at Sandbanks and Presqu’ile Provincial Parks on Lake Ontario. Dunes are also found along the Ottawa River160 at Westmeath (Constance Bay no longer has areas of open dunes, although there were dunes in this area historically).

Figure 16. Coastal dunes of the Ontario portion of the Mixedwood Plains Ecozone+.
image of southern Ontario
Long description for Figure 16

This map shows the distribution of coastal dunes in the region. In addition to the major dune systems listed in the text, coastal dunes are also scattered along the east coast of Lake Huron, and at additional locations on the north coast of Lake Erie and the northwest coast of Lake Ontario.

Source: Natural Heritage Information Centre, 2011147

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Open dune ecosystems are provincially rare161 and home to many rare plant species, such as little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), puccoon (Lithospermum caroliniense), fringed puccoon (Lithospermum incisum),indian grass (Sorghastrum nutans), and Canada wild rye (Elymus caandensis). Pitcher’s thistle (Cirsium pitcheri) and long-leaved reed grass (Calamovilfa longifolia var. magna) are also found in these ecosystems and both are endemic to the Great Lakes. At least 24 other provincially rare plant species are known to occur in the coastal dunes of the ecozone+.162

The endangered piping plover (Charadrius melodus) historically nested in the coastal dune areas of Great Lakes but was entirely missing from the Ontario portion of the ecozone+ by 1976.45 The plover started to return in 1993. In a study examining breeding success between 1993 and 2008,163 it was found that predation by merlins (Falco columbarius),another species once depleted in number and making a comeback, was responsible for most of the nest abandonment. Abandonment amounted to 5.7% of the marked plover population.

There are also many rare insects found in coastal dunes, including species of tiger beetles, grasshoppers, butterflies, and moths. Some, such as the Lake Huron locust (Trimerotropis huroniana), are globally rare.45

Coastal dunes are very fragile ecosystems which can be easily disturbed by both human and natural forces. As few as 200 dune crossings by hikers can kill dune vegetation.159,164 Shoreline hardening and the creation of groins, breakwalls, and piers which change the natural erosion and deposition of sand by water currents negatively impact dunes.165,166 Heat from bonfires on dunes kills the roots of adjacent plants.167 The lowering of lake levels and reduction in groundwater supplies that are predicted with climate change168 will have negative impacts on dune ecosystems. Development pressure is expected to continue along the shorelines of the Great Lakes.165

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