Introduction

Peatlands are a significant part of the landscape of continental western Canada and occupy an estimated 365,157 km2 or 20.8% of the total landscape of Alberta, Saskatchewan, and Manitoba, including 103,000 km2 in Alberta, 51,300 km2 in Saskatchewan, and 211,000 km2 in Manitoba. Fens make up 63% and bogs 37% of the peatland cover (Halsey et al. 1997; Vitt et al. 2000).

Patterned peatlands are characterized by microforms of open wet pools and carpets (flarks) separated by raised, often hummocky, shrubby or wooded strings. Sinuous, linear strings and flarks are oriented along the contours of the peatland surface and perpendicular to the direction of water flow when situated on gently sloping terrain forming a ribbed pattern, while on level ground the strings form a net or maze pattern, lacking orientation to the surrounding surface contours or water flow (Rietkirk et al. 2004; Eppinga et al. 2009).

Historically, patterned peatlands were first described from northern Fennoscandia, and since then several terms have been used to characterize these distinctive peatland landforms. According to Laitinen (2008), Cajander (1913) was the first to use the Finnish term ‘Aapamoore’ to describe a specific northern mire climatic type from northern Finland, with large often branching wetlands with the central parts having a distinct pattern of flarks and strings. However, since then the concept of aapa mire has either been as a regional vegetation concept for large minerotrophic mire complexes with not only areas with strings and flarks, but also those with mire expanse vegetation in their central parts without strings (Laitinen 2008; Rydin and Jeglum 2006) or a morphological peatland type characterized by flarks and strings, similar to Auer’s (1920) use of the German term ‘Strangmoor’ to describe individual patterned fens in Finland. Ruuhijärvi (1983) described aapa mires as ‘minerotrophic wet mires occurring in the middle or northern boreal vegetation zones. The often extensive centre of this mire-complex type is characterized by a pronounced surface pattern of flarks…and hummocky strings…’. These sites consist of wet areas, with distinct microforms—areas with pools of water or lawn vegetation (flarks) alternating with linear, drier hummocky areas (strings). In North America, similar patterning occurs in fens across the boreal region, but it is unclear how comparable patterned fens in North America are to those described from northern Europe.

Patterned fens are widely distributed in the boreal region, known from Fennoscandia (Ruuhijärvi 1983; Sjörs 1983), Russia (Botch and Masing 1983), and northeastern China (Wang et al. 2020). In the southern hemisphere, patterned fens have been reported from New Zealand (Mark et al. 1995), tropical Africa (Backéus 1989), and southern South America (Tierra del Fuego—Roivainen 1954) and Andean Colombia (David Cooper, pers. comm.)

In North America, patterned fens are frequent across the Canadian boreal region (Zoltai et al. 1988), from Labrador and Quebec (Foster et al. 1988; Arlen-Poutiot and Payette 2015; Robitaille et al. 2021), through Ontario (Sjörs 1963) the Hudson Bay Lowland (Abraham and Keddy 2005; Harris et al. 2020), Manitoba (Halsey et al. 1997), and British Columbia (MacKenzie and Moran 2004). In the west, patterned fens are reported as far north as the southern Yukon Territory (Watson Lake area—D. Vitt. pers. comm.) and Great Slave Lake, N.W.T. (Pakarinen and Talbot 1976) and they occur as far south as 37°57ʹ in northern California (Wolf and Cooper 2015), Yellowstone, Wyoming (Lemly et al. 2007, Lemly and Cooper 2011, 37°54ʹ in Colorado (Chimner et al. 2012), (Teton Co., Montana (Lesica 1986). In the east, patterned fens are known from northern Minnesota where they are extensive in the Red Lake Peatland (Glaser et al. 1981) and extend to Alborn Fen in St. Louis Co. (Jeremy Hartsock, pers. comm.), southern Wisconsin (Ozaukee Co.–Grittinger 1970), the Upper Peninsula, Michigan (Schoolcraft Co.–Heinselman 1965), and north-central Adirondacks, (New York New York Natural Heritage Program 2023).

Estimates for patterned fen abundances include 4,635 km2 in Alberta [4.5% of provincial peatlands], 6050 km2 [11.8%] in Saskatchewan, and 22,710 km2 [10.8%] in Manitoba (data extracted from (Halsey et al. 1997; Vitt et al. 2000). Patterned fens comprise 33,391 km2 or 9.1% of all peatlands across the three provinces or 1.9% of the terrestrial land cover (Vitt et al. 2000). Reference to the occurrence of patterned fens in western boreal Canada include Zoltai et al. (1988) who make only casual mention of northern ribbed fens with the statement that they are ‘very common in the Mid-Boreal and High Boreal Wetland regions…’ and described the vegetation and chemistry of one fen near Smith, Alberta. They make no mention of fens with net patterns. Patterned fens are not recognized in Ducks Unlimited’s Field Guide to the wetlands of the boreal plain (Smith et al. 2007). To our acknowledge, only five studies have been published describing the surface features, vegetation, and chemistry of patterned fens in Alberta; Swan Hills (Vitt et al. 1975), Rocky Mountain foothills (Slack et al. 1980), two studies of McClelland Wetland (Fort Hills—(Vitt et al. 2003, 2022), and Wood Buffalo National Park (Timoney 2001). Thus, although supposedly common across the boreal plain and frequently photographed from the air, patterned fens are largely unknown, even in areas where they are a characteristic part of the landscape.

Patterned fens are unique wetland landforms that provide habitats for rare species, have large deposits of carbon stored in peat deposits, and provide hydrological filters in many headwater areas (see overview by Slaughter and Cohen 2010), yet the lack of information on their occurrence and distribution in western Canada is a current knowledge gap. Currently in Alberta, as well across the western Canadian boreal forest, we lack an inventory of patterned fens. Here, we utilized Google Earth remote sensing to survey the western boreal forest area of the province of Alberta for patterned fen landforms with four objectives: (1) document the number and locations of all patterned fens in the province and provide a database for these locations; (2) distinguish between fens with ribbed patterns (ribbed fens) and those with net patterns (reticulate fens), (3) determine the regional variation in patterned fen occurrences, and (4) describe the morphological forms of patterned fens, recognizing differences as distinctive peatland site-types.

Materials and methods

Study area

Alberta is the fourth-largest province of Canada situated between 49° to 60°N latitude, and approximately 1230 km in length north to south. Bounded by the Canadian Rocky Mountains to the west, it is the westernmost of the three prairie provinces. Seventy percent (or 465,100 km2) of the province consists of boreal/montane forest, a mosaic of lakes, wetlands (mostly bogs and fens), and upland forest (dominated by Picea glauca, Populus tremuloides, and/or Pinus spp.). Alberta’s boreal forest region has a subhumid continental climate (Little-Devito et al. 2019), characterized by cold dry winters and short cool moist summers. Precipitation varies from 600 to 700 mm along the benchlands of the eastern slopes of the Rocky Mountains to 450–500 mm across the lowlands and plains of northern Alberta. The upland plateaus of boreal Alberta and western montane benchlands receive slightly more precipitation (500–550 mm) than the lowlands (www1.agric.gov.ab.ca, accessed August 15, 2023). Average (mean) temperatures vary from − 4 °C to + 3 °C (Halsey et al. 1995) with summer averages from 13.0–15.5 °C.

Methods

We examined the part of the province of Alberta north of the southern limit of Picea mariana (Zoltai 1975). We used Google Earth Pro as a geobrowser that is free and readily available to the general public. It also allows creation of geolocated data that are accessible from kmz files. For purposes of replication, we placed latitudinal lines across the entire province every 2.4 km (01′17.76″) and systematically viewed the contiguous areas between lines at an approximate elevation of 1500 m. All three co-authors participated in identification of patterned fens after joint training sessions; the first author reviewed all georeferenced files for consistency. Several areas of the province were examined by more than one person. Each patterned fen was identified and marked as ‘ribbed’ (wetlands having closely spaced, narrow flarks (areas submerged or with vegetated carpets three times as long as wide) separated by linear, raised, hummocky strings arranged perpendicular to the surface contours) or ‘reticulate’ (wetlands having a network of broad flarks (oval or isodiametric in shape), separated by linear, raised, hummocky strings and not arranged along surface contours) and given a unique identification number. Occasionally, saline wetlands, wherein irregularly shaped pools (without vegetation) form from upwelling of sodic ground water and may be separated by broad, raised areas that resemble the patterning in non-saline wetlands. These sodic, irregularly patterned wetlands were not included in our surveys. Patterned fens influenced by a single hydrological source and within an individual peatland complex were considered as one site (e.g., fens on either side of a water body); while those influenced by separate hydrological sources and separated by upland areas were considered as separate sites. As almost all sites are remote and not accessible by road, except for sites wherein we have carried out previous research, individual sites were not visited. We chose a representative subset of 55 ribbed fens (5% of the total number of ribbed fens) and 25 reticulate fens (10% of the total number of reticulate fens). Ribbed fens were randomly selected from three areas with a high number of ribbed fens—one-third each from the Caribou Mountains, the Birch Mountains, and the Western Benchlands, while reticulate fens were randomly selected from the northeastern area of the province where they are most abundant. Using elevations provided by Google Earth Pro, we recorded the elevation at the first and last flark and recorded the length of the patterning between these flarks based on the ‘Add Path’ program in Google Earth Pro and calculated the slope of the fen. We examined the variation in distribution of patterned fens by identification of major physiographic features within the province (Pettapiece 1986), paying particular attention to elevational highs and lows within the boreal region of the province. We categorized the patterned fens into six morphological types based on (1) position on the landscape, (2) shape and size of the ribbed area of the fen, (3) association with other peatland landforms, and 4) structural complexity.

Results

Patterned fens in Alberta

We identified 1083 ribbed fens and 250 reticulate fens in the province. Ribbed fen locations are provided in Supplementary files 1 (excel) and 2 (kmz). Reticulate fen locations are provided in Supplementary files 3 (excel) and 4 (kmz).

Regional variation in occurrence of ribbed fens

Approximately 57% of the ribbed fens are boreal in distribution and 43% occur on the montane benchlands of the eastern slopes of the Rocky Mountains (Fig. 1). The 612 boreal ribbed fens are equally divided along the latitudinal gradient, with about 33% distributed between 54–56°N, 56–58°N, and 58–60°N latitude. Almost all boreal ribbed fens occur in the eastern half of the province. The southernmost ribbed fen was at 51.042ʹN latitude, just west of Calgary. The boreal ribbed fens are clustered on several high elevation plateaus, physiographically referred to as Northern Alberta Uplands Pettapiece 1986). Of the 612 ribbed fens in boreal Alberta, 436 (71%) are associated with six regional upland plateaus, all with elevations between 600 and 1400 m (https://en-ca.topographic-map.com/ accessed August 1 2023). All of these upland areas have morainal deposits with occasional deposition of glacial-fluvial materials (Pettapiece 1986). All serve as headwater catchments for large rivers of the province (www.northern Alberta backroad mapbook.com, accessed Auguest 20, 2023).

Fig. 1
figure 1

Map of Alberta with locations of 1,083 ribbed fens (black circles), with outlines of major upland areas in the boreal region of the province. Lakes with ripple marks. Edmonton (north) and Calgary (south) are shown as open circles. Inset: Names of the upland areas mentioned in the text. Physiographic areas and names from Pettapiece 1986)

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The most conspicuous clusters of ribbed fens are as follows: Caribou Mountains Upland and headwaters of Ponion River: Ribbed fens are especially numerous (93 ribbed fens identified) along the northwestern slopes of the plateau on the Melvin Plain. Birch Mountains Upland and headwaters of Mikkwa, McIvor, and Birch Rivers: Ribbed fens are numerous (29) on the northwestern plateau (headwaters of the Birch River) and the southeastern plateau (19) (headwaters of the McIvor River); however, they are not present on the Peerless Lake Upland to the south. Firebag Hills Upland and headwaters of the Firebag River: Ribbed fens are especially abundant on Muskeg Mountain (8) and areas to the east (5). Stony Mountain Upland and headwaters of the Christina River: Ribbed fens are numerous (55) throughout the Crow Lake Upland, and especially numerous northward, associated with the headwaters of the Christina River. Moostoos Hills Uplands and headwaters of the Winefred and Sand Rivers: This is the southernmost region with high abundance of ribbed fens in eastern Alberta, a total of 130 ribbed fens were identified in this region. Swan Hills Upland and headwaters of Freeman and Isogun Rivers: 11 ribbed fens are found on the elevational high of the area, with 15 occurring on the eastern slopes and 43 on areas with aeolian and fluvial sediments west of Highway 44. Clear Hills Upland and headwaters of Chinchaga and Notikewan Rivers: This is the only boreal area in the western part of the province with abundant occurrences of ribbed fens, with 36 ribbed fens occurring along the slopes of Halvorson Ridge and areas to the south, most in association with small lakes. Two additional uplands—the Cameron Hills Upland (northwestern corner of province) and Buffalo Head Hills Upland – (north central Alberta), have almost no ribbed fens (one in each area). Likewise, the Pelican Mountains (east of Lesser slave Lake) have few patterned fens; noteworthy is one very large peatland complex with several ribbed fens on the eastern slope of Marten Mountain. Western and Grande Cache Benchlands: North of the Athabasca River, ribbed fens are common on the Berland Benchlands and Entrance Benchlands, but absent farther north on the Kakwa and Cutbank benchlands. South of the Athabasca River, ribbed fens are abundant on the Wolf Lake (Edson area), O’Chiese, and Shunda (west of Rocky Mountain House) Benchlands. Ribbed fen occurrences extend eastward through the Edson Plain, Crimson Lake Plain, and Cynthia Upland, and a few occur as far east as the Edmonton area.

Regional variation in occurrence of reticulate fens

Reticulate fens have broad flarks with strings forming a net or reticulate pattern. Flarks are generally oval in shape and somewhat longer than wide, with no apparent orientation to slope. Strings are linear and appear similar to those of ribbed fens. Of the 250 reticulate fens identified, 154 (61%) occur north of 57° latitude. 211 (84%) of the 250 fens occur north of 54° latitude, with only 39 (16%) occurring southward (Fig. 2). The southernmost reticulate fen is at 52.076ʹN latitude.

Fig. 2
figure 2

Map of Alberta with locations of 250 reticulate fens (Black circles), with outlines of areas associated with clusters of reticulate fens. Lakes with ripple marks. Edmonton (north) and Calgary (south) are shown as open circles. Areas 2 and 3 are areas without reticulate fens. Inset: Names of the areas mentioned in the text. Physiographic areas and names from Pettapiece 1986)

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As with ribbed fens, reticulate fens occur in clusters of sites in several specific areas of the province, as follows: Great Slave Plain: 72 (28%) of the reticulate fens occur on the Great Slave Plain, a physiographic region with little elevational relief and dominated by glacial lacustrine and glacial fluvial materials. A portion of these reticulate fens occur in Wood Buffalo National Park wherein saline wetlands are common and sometimes patterned (Timoney 2001).

Mikkwa Plain: About 31 (13%) of the reticulate fens are clustered in a small area between the Wabasca and Birch Rivers, south of the confluence with the Peace River. This area is part of the Vermilion Lowland with glacial lacustrine and morainal materials. Hay River Plain: 25 (10%) per cent of the reticulate fens occur in a band on the Hay River Plain (east and southeast of Zama City) in northwestern Alberta, an area with glacial lacustrine sediments. WinefredLake/Moostoos Hill Upland: Farther south and along the Saskatchewan border, a set of 27 (11%) of reticulate fens are distributed on the Winefred Lake/Moostoos Hill Upland, areas with glacial-fluvial and morainal substrates. Western Benchlands: On the western Benchlands adjoining the Rocky Mountain foothills are a scattering of reticulate fens with 33 (13%) occurring in the Kakwa (northern areas) and Wolf Lake Benchlands (southern areas), both areas with morainal substrates.

The remaining 25% of reticulate fens are found scattered in isolated locations northward in the province. In comparison to these physiographic regions with high frequency of reticulate fens, several regions of the province stand out as having only a few (or none) reticulate fens; these include all of the regional boreal uplands and the Tazin River Upland with granite (Precambrian Shield) substrates and the Athabasca Plain, with mostly sandstone substrates, the latter both in extreme northeastern Alberta.

Variation in size and slope of patterned fens

Ribbed fens are extremely variable in length, from less than 0.25 km to over 7 km long. Most ribbed fens are under 1.5 km in length and occur on sloping terrain. Regressing elevational change against fen length provides a significant relationship (r2 = 0.609) with a predicted elevational change of 3.78 m for every 1000 m of fen length (Fig. 3). Comparatively, reticulate fens have a predicted elevational difference of 1.08 m for every 1000 m of fen pattern (r2 = 0.311—Fig. 3).

Fig. 3
figure 3

Elevational change (meters) plotted against ribbed fen length (meters × 10) for 55 ribbed fens and 25 reticulate fens (triangles); filled circles are boreal ribbed sites; open circles are montane ribbed circles. Ribbed fen regression: r2 = 0.609; y = 0.6608 + 0.0312x; reticulate fen regression: r2 = 0.311; y = 0.0054x + 0.5409

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Morphological variation in patterned fens

Patterned fens have variable vegetation and water chemistry and vary in shape, size, structural pattern, and how they associate with the surrounding landscape. Here we define six morphological types. (1) Reticulate Fens occur on level substrates where water flow is multidirectional (Halsey et al. 1995), and usually are elliptical to isodiametric in shape. The strings may be well-developed and form complete ellipses (Fig. 4a), or in other cases strings are poorly developed and discontinuous across the wetland. Some reticulate fens have patterns formed under semi-aquatic conditions, with longitudinal sedge-dominated areas surrounding pools of open water. Sodic wetlands (Timoney 2001) in northeastern Alberta can have pools of water surrounding by string-like ridges forming reticulate wetlands on shallow peat. (2) Lake-shore ribbed fens occur bordering small lakes, with broad, larger, ponded flarks close to the lake and smaller narrow flarks with distance. Elevational gradients may slope downward toward the lake (Fig. 4b) or slopes may decrease in elevation away from the lake (Fig. 4c). (3) Ribbed fens within peatland complexes. Peatland complexes have a diversity of landforms, including bog islands, non-patterned moss-graminoid fens, and small lakes, all intermixed with ribbed fens (Fig. 4d). Superficially these may resemble aapamires of northern Finland (Laitinen 2008). Peatland complexes occur scattered on regional uplands, but are especially abundant on the Stony Mountain Upland. (4) Linear ribbed fens occur in long, narrow, gently sloped valleys, and often are more than one kilometer long, with a variety of broad and narrow flarks (Fig. 5a). (5) Ribbed fens of drainage divides have water flow in opposite directions away from the central point of highest elevation. Large, oval flarks occur centrally with smaller, linear flarks organized down slopes, away from the central elevational high (Fig. 5b). (6) Isolated ribbed fens are common on the western benchlands and occur in wooded terrain on gently sloped ground with no water bodies nearby. They may be quite small (Fig. 5c) or large with several branches. (Fig. 5d).

Fig. 4
figure 4

Variation in morphology of patterned fens in Alberta. a Reticulate fen with similar elevations across the width of the fen and < 1 m elevational change along the length of the site. Fen is located on the Great Slave Plain. b Ribbed fen bordering lake (right of image) with elevation slope toward the lake (McClelland Wetland and Lake, Fort Hills). c Ribbed fen bordering small lake with 4.3 m elevational slope away from the lake (Caribou Mountains). d Large ribbed fen associated with bogs (darker fine textured areas), non-patterned fens (light areas east of central stream), and small lakes. Note reticulate fen in lower right corner. (Stony Mountain Upland)

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Fig. 5
figure 5

Variation in morphology of patterned fens in Alberta. a Long (0.9 km) linear fen with a 3.3 m drop in elevation (Harrison River Plain). b Long (3.8 km) linear fen with elevational drop of 4.0 m in two directions originating from center divide (white dot) (Birch Mountains Upland). c Small isolated, elliptical ribbed fen with no ponded flarks—0.24 km long with 1.2 m elevational change (Western Benchlands). d Large, branched, isolated ribbed fen 0.9 × 1.1 km wide with a 7.0 m elevational change (Swan Hills)

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Discussion

Effects of climate on the distribution of patterned fens

Modeled annual mean temperatures for the 1951–1980 time period for boreal continental western Canada (Halsey et al. 1995) show the 1.0 °C isotherm runs diagonally through northeastern and northcentral Alberta, decreasing to − 3.0 °C in extreme northeastern Alberta and to − 4.0 °C in extreme northwestern Alberta. Bog landforms with current and thawing permafrost parallel these isotherms, with 30% of the bogs containing permafrost at the − 0.4 °C isotherm (Halsey et al. 1995).

Patterned fens also are numerous at and north of these isotherms

In Manitoba, patterned fens occur preferentially where seasonal frost persists well into the growing season in areas dominated by non-permafrost bogs (Halsey et al. 1997) and well south of areas dominated by permafrost features. Similarly in Alberta, numerous patterned fens occur south of the regions with abundant permafrost bogs. This is especially apparent in the montane benchlands, where annual mean temperatures are + 2.0–3.0 °C and permafrost is not known, yet patterned fens are abundant.

The lack of abundant patterned fens in northwestern Alberta (other than within the Clear Hills Upland) corresponds to the general decrease in wetlands in the area (Vitt et al. 2001) and to the northward extension of the Dry Mixedwood and Peace River Parkland natural subregions of the province (https://www.albertaparks.ca, accessed August 20, 2023). Southward, patterned fens do not occur in the Aspen Parkland (defined by the absence of coniferous trees—Bird 1961).

The ecological importance of patterned fens in Alberta

Much of eastern and central boreal Canada is underlain by acidic granitic rocks of the Canadian (Precambian) Shield. These substrates yield watersheds poor in nutrients and cations, and Sphagnum-dominated acid fens are common (Foster and King 1984; Garneau et al. 2018). These acidic substrates occur in Alberta only in the extreme northeastern corner of the province (physiographically the Tazin River Upland). A large majority of the remainder of Alberta is underlain by the western Canadian sedimentary basin, rich in carbonates from Paleozoic marine transgressions. Modern-day watersheds across much of the province are influenced by carbonate-rich waters high in base cations, resulting in peatlands dominated by circumneutral and alkaline fens at lower elevations and those affected by regional drainage from the Canadian Rocky Mountains. The carbonate-rich watersheds in western Alberta prohibit development of acid fens, and ombrogenous bogs are rare. These carbonate-rich fens (both patterned and non-patterned) have a species-rich plant flora and are uncommon in areas underlain by the Canadian Shield. Sphagnum-dominated acid fens are restricted to sites less affected by carbonate-rich waters such as on the regional upland plateaus where low drainage divides provide gentle sloping terrain for patterned fen development.

Peatlands of boreal western Canada occur in a subhumid climatic regime characterized by relatively low precipitation. Most peatlands are dominated by coniferous tree species, with nearly all bogs having a well-developed tree layer without pool and carpet vegetation. Likewise, 62% of fens across the boreal zone of western Canada have a shrub or tree layer (Vitt et al. 2001), with limited wet microhabitats. As a result, open pool and carpet microhabitats are uncommon in fens of the region, and largely restricted to moss-graminoid-dominated (open) fens. Species richness, especially for ground layer species, is largely associated with the number of microhabitats along the wet to dry topographic gradient (Vitt et al. 1995). Patterned fens are especially noteworthy for a relatively large topographic gradient, from flarks with wet pools and carpets to dry hummocky strings and contain a richness of plant species not found in other habitats. The combination of carbonate-rich watersheds with circumneutral and alkaline fens in montane Alberta, regional upland plateaus in boreal Alberta with acid fens, and the presence of wet microhabitats provide a highly diverse set of habitat conditions making patterned fens an important part of the provincial landscape.

Variation in vegetation and chemistry

Over the past several decades much discussion and debate have taken place over how common patterned fens are in Alberta and if they have high conservation value. Previous mapping of wetlands in Alberta has demonstrated that patterned fens are fairly common (Vitt et al.1996), yet they occupy only 1.0% of the boreal-montane forest area of the province (data from Vitt et al. 2000). Species considered rare have been associated with ribbed fens (Vitt et al. 2003). However, the lack of information on vegetation and associated environmental variables for patterned fens has left many questions. Based on the few studies available (Slack et al. 1980; Timoney 2001; Vitt et al. 1975, 2022; Volik et al. 2017) and our own field knowledge, ribbed fens have variable vegetation and chemical components and occupy the entire minerotrophic gradient. Ribbed fens in the province are either dominated by (1) Sphagnum associated with acidic pH and oligotrophic water, (2) true mosses with circumneutral to basic pH, high alkalinity in some cases, and mesotrophic water, or (3) have a limited ground layer with high concentrations of sodium. Acid fens, with a high diversity of Sphagnum, are more common on low drainage divides and associated with regional uplands where the influence of calcareous groundwater is less. The ground layer contains a rich diversity of species of Sphagnum, including S. fallax, S. majus, S. jensenii, S. lindbergii, and S. angustifolium. Although sedges are not abundant, species include Carex limosa, C. trisperma, and Scheuchzeria palustris. Strings are characterized by hummock-forming Sphagnum species such as S. fuscum, S. capillifolium, and S. magellanicum, as well as Aulacomnium palustre, Tomentypnum falcifolium, Betula glandulosa, Rhododendron groenlandicum, and Picea mariana (Vitt et al. 1975). In comparison, circumneutral and alkaline fens are most common in areas with calcareous groundwaters. The ground layer contains a high diversity of true mosses and only a few species of Sphagnum. Species include Scorpidium scorpioides, S. revolvens, Hamatocaulis vernicosus, Meesia triquetra, Pseudocalliergon trifarium, Calliergon giganteum, and Sphagnum subsecundum. Strings are characterized by Tomentypnum nitens and Sphagnum fimbriatum, with Betula glandulosa, B. pumila, Salix spp., and Larix laricina as the dominant tree species. Sedges are comparably more abundant than in acid fens, with a number of species, including Carex lasiocarpa, C. aquatilis, C. diandra, C. chordorrhiza, C. interior, C. utriculata, and Triglochin maritima (Slack et al. 1980; Hartsock et al. 2021). Thirdly, brackish and sodic wetlands may be ribbed when occurring on sloping substrates (Volik et al. 2017). These wetlands, with high concentrations of sodium, have a poorly developed ground layer of mosses and unique vascular plants including Juncus balticus and Triglochin maritima (Hartsock et al. 2021). Timoney (2001) described two ribbed and reticulate patterned salt marshes from northeastern Alberta wherein bryophytes and characteristic fen species were nearly lacking and marsh halophytes predominant. He termed these ‘interior patterned saline marshes’ and provided a list of the dominant species (Timoney 2001).

Although it is not possible to determine if individual patterned fens are acid, circumneutral, alkaline, or sodic from Google Earth surveys, extensive observations and vegetation surveys (Vitt, personal communication) in the province suggest a regional pattern in the distribution of fen site-types—circumneutral and alkaline fens are most common on the western benchlands, acid fens are most abundant on the regional uplands in eastern Alberta, and sodic wetlands, although not common, are present on the Great Slave Plain in northeastern Alberta. To our knowledge, there is only one study of reticulate fens (Timoney 2001) in the province.

Variation in terrain contours for ribbed fens

Unlike the extensive and nearly continuous areas of patterned fens in the Hudson Bay Lowland, patterned fens in Alberta occur as single landforms or as part of peatland complexes. Ribbed fens form on gentle sloping terrain centering on slopes of 1:200 to 1:300; however, there appear to be marked exceptions. In the Swan Hills, a large isolated ribbed fen (Fig. 5d) has a surface slope of 1:95, while the ribbed fen at McClelland Lake (Fig. 4b) has a surface slope of 1:1,500 (5 m drop over 7.75 km). These wide variances in surface slopes suggests that not only do slope characteristics relate to the occurrence of ribbed fens, but also amount of water movement. A steeper slope with less water flow may be equivalent to a lesser slope with greater water flow. This issue needs further study. Furthermore, the study site at McClelland Lake demonstrates that surface slope changes over time. At this site, the original mineral surface had an average slope of 1:750 (10.1 m drop over 7.75 km) and over the 11,000 year history of the fen the slope was reduced by half owing to differential rates of peat accumulation (Vitt et al. 2023), indicating the current slope conditions may be much different than previous gradient conditions, and early development of patterning may take place under different conditions.

Conclusions and implications

Conservation and the need for further study

Here we have recognized patterned fens that vary not only along the minerotrophic gradient (sites with calcareous alkaline, circumneutral, or acidic water chemistry), but also have a complex set of morphological types. To our knowledge, there are no studies that provide data to associate these six morphological patterned fen types with environmental or geological characteristics, nor have western Canadian patterned fens been compared to those in other parts of the world. A systematic survey of patterned fens across the province would enhance our knowledge base and clarify relationships between the various characteristics of patterned fens. Such a survey would provide much needed data on species rarity and carbon storage in the province. We argue here that patterned fens follow a general minerotrophic gradient across the province – calcareous, rich fens westward and acidic poor fens to the east; however, there are no data on abundance estimates for patterned fens along this minerotrophic gradient, and this also needs further study. These are all areas that need to be explored in future research.

Patterned fens have developed over the past 11,000 years and are maintained by complex small-scale feedback mechanisms (Eppinga et al. 2009; Harris et al. 2020). Changes in the hydrology and chemistry of the surrounding watershed may have strong impacts on these unique peatland systems (Quinton and Roulet 1998). Additionally, climatically induced changes in hydrology (Arlen-Poutiot and Payette 2015) have influenced changes in patterning. This inventory of patterned fens should serve as baseline data for land-use planning and future development in the province, especially in oil and gas exploration and development, access road placement, and planning for areas to be conserved.

In our survey of patterned fens, we observed that at present, few of the 1,300 patterned fens in the province have markers of severe disturbance; however, disturbances from oil/gas exploration, production wells, and associated access roads are present in many associated watersheds. These nearby disturbances have the potential for changing wetland hydrological processes that directly have the potential to affect species changes and fine-scale ecological processes within the patterned fens, and in turn may alter flark/string maintenance. With continued expansion of industrial activities in the western boreal forest, patterned fens should be recognized as unique, intrinsically valuable landforms that have value in habitats for rare flora and endangered wildlife, and contain significant deposits of organic matter that serve as long-tern carbon depositories. Although many of the patterned fens are located in Wood Buffalo National Park or in one of the provincial conservation areas, to our knowledge there is no patterned fen specifically targeted for preservation in the province. This lack of concern for patterned fens is compounded by the lack of information on their hydrology, vegetation, and ecology. It is remarkable that these unique and beautiful landforms have not been better recognized in the province. Although patterned fens are known from many areas of the world, the diversity of forms found in Alberta should provide a stimulus for study and conservation.

Summary and implications

The presence of 1333 patterned fens in Alberta indicates that these are not rare wetlands. Similarly in Finland, Ruuhijärvi’s map (1960) showed abundant ‘aapamoor’ that provide a characteristic zone in northern Finland recognized worldwide. Here we identify that the occurrence of patterned fens in the province is not random. Ribbed fens are most abundant on high elevational plateaus in the northern and eastern portions of the province, and on the Western Benchlands on the eastern slopes of the Rocky Mountains, and these should be recognized as an important part of the regional landscape. Reticulate fens are most numerous on low elevation plains in the northern portions of the province and likewise are characteristic of this part of the province. Ribbed fens occur on gentle slopes with variable grades, mostly on morainal substrates, while reticulate fens occur on level ground, mostly with glacial-fluvial or glacial-lacustrine deposits. Future investigation of patterned fens may result in significant changes in our understanding of rare flora and fauna and lead to development of more refined conservation planning for the province. For example, some species that are rarely collected may be restricted to pool and carpet microhabitats generally associated with flarks and occur only in patterned fens. Furthermore, patterned fens include the longest record of peatland development since the last glaciation (Vitt and House 2023), and provide clues to how the western Canadian landscape has developed over the last 11,000 years, a heritage that should be recognized and preserved.