Big Lake-Seven Beaver
Inland strand beach on the shore of Seven Beaver Lake.
The Big Lake-Seven Beaver RNA on the Superior National Forest protects part of the largest, most complex peatland in the Northern Superior Uplands Section, and part of the largest unfragmented patch of mature upland forest in Minnesota outside of the Boundary Waters Canoe Area Wilderness. These plant communities still resemble the presettlement vegetation of the area described in the 1882 Public Land Survey. The lack of roads, absence of recent large-scale logging, and large size of the RNA allow for natural functioning of ecological processes, supporting an array of plants and animals found in these ecosystems.
Ecological and Physical Description
Ecological Classification & Inventory
- Sections: Mixed Forest Province, Northern Superior Uplands Section
- Subsections: Laurentian Uplands Subsection (212Le)
- Landtype Associations: Seven Beaver Peatland (212Le08), with the western end in the Big-Bird Lake Moraine LTA (212Le11)
Annual precipitation averages 28.7 inches (73 cm); Average seasonal snowfall is 65.1 inches (165.4 cm).
Brimson (station ID number: GHCND: USC00210989, latitude 47.25°, longitude -91.86°). The station is about 18 mi (29 km) south of the RNA.
The Big Lake-Seven Beaver RNA is located in the Superior Uplands physiographic province which is actually the southernmost lobe of the Laurentian Upland Province—an important part of the Canadian Shield which forms part of the North American Craton—the extremely stable part of the North American continent. Within the boundaries of the RNA, there are four distinct bedrock lithologies: an anorthositic intrusion, a troctolitic western margin intrusion, gabbro of the Greenwood Lake Intrusion, and troctolites of the South Kawishiwi Intrusion.
Soils are characterized by predominantly flat to concave, acidic, very deep, organic deposits formed in Rainy lobe ground moraine depressions in central and eastern portions of the RNA. A carpet of sphagnum moss covers the upper mantle of the deposit and usually thickens towards the center of the RNA. Acidity tends to lessen with depth, ranging from 3.5 to 4.5 within the sphagnum mantle and from 4.5 to 5.5 in the lower tiers (USDA 2022). These very poorly drained organic soils (with water tables at or near the soil surface for much of the year), fall primarily within the Greenwood series, associated with vast expanses of lowland black spruce-dominated peatlands, and linear map units of the mucky Bowstring series, primarily alder swamps and wet meadows north of Big Lake and along flood prone areas of the North River (NRCS 2022).
Seven Beaver Lake borders a portion of the southeast portion of the RNA and is a large, shallow, undeveloped lake, its shoreline primarily open shrub and graminoid dominated wetlands. Wild rice grows sparsely throughout much of the lake, including the mouth of the North River. Big Lake is deeper with a densely forested shoreline. Big Lake borders the western portion of the RNA with forested uplands that include vernal pools.
The North River and its floodplain dominate the eastern portion of the RNA and is part of the uppermost portion of the St. Louis River. The North River, for most of its length, is only a few yards wide, expanding to 30 yards at the mouth (Fedora 2005). Its floodplain is dominated by extensive open rich fens. The corridor supports extensive populations of two rare plant species.
Flora and Fauna
Common Plant Species
| Scientific Name | Common Name | Category | At Risk | Notes |
|---|---|---|---|---|
| Abies balsamea | Balsam Fir | Trees and Shrubs | ||
| Acer rubrum | Red Maple | Trees and Shrubs | ||
| Acer spicatum | Mountain Maple | Trees and Shrubs | ||
| Alnus incana spp. rugosa | Speckled/Tag Alder | Trees and Shrubs | ||
| Amelanchier sp. | Serviceberry/Juneberry species | Trees and Shrubs | ||
| Andromeda polifolia | Bog Rosemary | Trees and Shrubs | ||
| Betula papyrifera | Paper Birch | Trees and Shrubs | ||
| Betula pumila | Bog Birch | Trees and Shrubs | ||
| Chamaedaphne calyculata | Leatherleaf | Trees and Shrubs | ||
| Diervilla lonicera | Northern Bush Honeysuckle | Trees and Shrubs | ||
| Kalmia polifolia | Bog Laurel | Trees and Shrubs | ||
| Larix laricina | Tamarack | Trees and Shrubs | ||
| Ledum (=Rhododendron) groenlandicum | Labrador Tea | Trees and Shrubs | ||
| Lonicera canadensis | American Fly Honeysuckle | Trees and Shrubs | ||
| Myrica gale | Sweet Gale | Trees and Shrubs | ||
| Picea glauca | White Spruce | Trees and Shrubs | ||
| Picea mariana | Black Spruce | Trees and Shrubs | ||
| Pinus banksiana | Jack Pine | Trees and Shrubs | ||
| Pinus strobus | Eastern White Pine | Trees and Shrubs | ||
| Populus tremuloides | Quaking Aspen | Trees and Shrubs | ||
| Ribes triste | Red Currant | Trees and Shrubs | ||
| Rosa acicularis | Prickly Rose | Trees and Shrubs | ||
| Rubus idaeus spp. strigosus | Grayleaf Red Raspberry | Trees and Shrubs | ||
| Sorbus decora | Showy Mountain Ash | Trees and Shrubs | ||
| Thuja occidentalis | Northern White Cedar | Trees and Shrubs | ||
| Vaccinium angustifolium | Lowbush Blueberry | Trees and Shrubs | ||
| Arceuthobium pusillum | Eastern Dwarf Mistletoe | Epiphytes | ||
| Agrostis scabra | Rough Bentgrass | Grasses, Sedges, and Rushes | ||
| Calamagrostis canadensis | Bluejoint | Grasses, Sedges, and Rushes | ||
| Carex brunnescens | Brownish Sedge | Grasses, Sedges, and Rushes | ||
| Carex chordorrhiza | Creeping Sedge | Grasses, Sedges, and Rushes | ||
| Carex cryptolepis | Northeastern Sedge | Grasses, Sedges, and Rushes | ||
| Carex disperma | Softleaf Sedge | Grasses, Sedges, and Rushes | ||
| Carex intumescens | Greater Bladder Sedge | Grasses, Sedges, and Rushes | ||
| Carex lasiocarpa | Wiregrass/Woolyfruit Sedge | Grasses, Sedges, and Rushes | ||
| Carex michauxiana | Michaux’s Sedge | Grasses, Sedges, and Rushes | ||
| Carex magellanica ssp. irrigua | Boreal Bog Sedge | Grasses, Sedges, and Rushes | ||
| Carex stricta | Tussock/Upright Sedge | Grasses, Sedges, and Rushes | ||
| Carex tenuiflora | Sparseflower Sedge | Grasses, Sedges, and Rushes | ||
| Carex trisperma | Three-seeded Sedge | Grasses, Sedges, and Rushes | ||
| Carex utriculata | Northwest Territory Sedge | Grasses, Sedges, and Rushes | ||
| Dulichium arundinaceum | Three-way Sedge | Grasses, Sedges, and Rushes | ||
| Eleocharis elliptica | Elliptic Spikerush | Grasses, Sedges, and Rushes | ||
| Eleocharis palustris | Common Spikerush | Grasses, Sedges, and Rushes | ||
| Eriophorum tenellum | Few-nerved Cottongrass | Grasses, Sedges, and Rushes | ||
| Glyceria canadensis | Rattlesnake Mannagrass | Grasses, Sedges, and Rushes | ||
| Juncus brevicaudatus | Narrowpanicle Rush | Grasses, Sedges, and Rushes | ||
| Rhynchospora alba | White Beaksedge | Grasses, Sedges, and Rushes | ||
| Schoenoplectus acutus | Hardstem Bulrush | Grasses, Sedges, and Rushes | ||
| Scirpus cyperinus | Woolgrass | Grasses, Sedges, and Rushes | ||
| Scirpus pedicellatus | Stalked Bulrush | Grasses, Sedges, and Rushes | ||
| Torreyochloa pallida var. fernaldii | Fernald’s False Mannagrass | Grasses, Sedges, and Rushes | ||
| Zizania palustris | Northern Wild Rice | Grasses, Sedges, and Rushes | ||
| Aralia nudicaulis | Wild Sarsaparilla | Forbs and Sub-Shrubs | ||
| Athyrium filix-femina ssp. angustum | Subarctic Lady Fern | Forbs and Sub-Shrubs | ||
| Cicuta bulbifera | Bulblet-bearing Water Hemlock | Forbs and Sub-Shrubs | ||
| Circaea alpina | Small Enchanter’s Nightshade | Forbs and Sub-Shrubs | ||
| Clintonia borealis | Bluebead Lily | Forbs and Sub-Shrubs | ||
| Comarum (=Potentilla) palustre | Marsh Cinquefoil/Purple Marshlocks | Forbs and Sub-Shrubs | ||
| Coptis trifolia | Threeleaf Goldthread | Forbs and Sub-Shrubs | ||
| Cornus canadensis | Bunchberry | Forbs and Sub-Shrubs | ||
| Cypripedium acaule | Moccasin Flower/Stemless Ladyslipper | Forbs and Sub-Shrubs | ||
| Drosera intermedia | Spoonleaf/Intermediate Sundew | Forbs and Sub-Shrubs | ||
| Drosera rotundifolia | Roundleaf Sundew | Forbs and Sub-Shrubs | ||
| Dryopteris carthusiana | Spinulose Wood Fern | Forbs and Sub-Shrubs | ||
| Equisetum fluviatile | Water Horsetail | Forbs and Sub-Shrubs | ||
| Equisetum sylvaticum | Woodland Horsetail | Forbs and Sub-Shrubs | ||
| Galium triflorum | Fragrant Bedstraw | Forbs and Sub-Shrubs | ||
| Gaultheria hispidula | Creeping Snowberry | Forbs and Sub-Shrubs | ||
| Geocaulon lividum | False Toadflax | Forbs and Sub-Shrubs | ||
| Goodyera repens | Lesser Rattlesnake Plantain | Forbs and Sub-Shrubs | ||
| Gymnocarpium dryopteris | Western Oak Fern | Forbs and Sub-Shrubs | ||
| Huperzia lucidula | Shining Firmoss/Clubmoss | Forbs and Sub-Shrubs | ||
| Hypericum majus | Large St. Johnswort | Forbs and Sub-Shrubs | ||
| Iris versicolor | Harlequin Blueflag Iris | Forbs and Sub-Shrubs | ||
| Lathyrus ochroleucus | Cream Pea | Forbs and Sub-Shrubs | ||
| Linnaea borealis | Twinflower | Forbs and Sub-Shrubs | ||
| Lycopodium annotinum | Stiff Clubmoss | Forbs and Sub-Shrubs | ||
| Lycopodium (=Dendrolycopodium) dendroideum | Tree Groundpine | Forbs and Sub-Shrubs | ||
| Lycopus uniflorus | Northern Bugleweed | Forbs and Sub-Shrubs | ||
| Lysimachia thyrsiflora | Tufted Loosestrife | Forbs and Sub-Shrubs | ||
| Maianthemum canadense | Canada Mayflower | Forbs and Sub-Shrubs | ||
| Maianthemum (=Smilacina) trifolium | Threeleaf False Lily-of-the-Valley | Forbs and Sub-Shrubs | ||
| Mitella nuda | Naked Miterwort | Forbs and Sub-Shrubs | ||
| Mentha arvensis | Wild Mint | Forbs and Sub-Shrubs | ||
| Moneses uniflora | One-flowered Shinleaf | Forbs and Sub-Shrubs | ||
| Monotropa uniflora | Ghost-pipe | Forbs and Sub-Shrubs | ||
| Nuphar lutea ssp. variegata | Variegated Yellow Water-lily | Forbs and Sub-Shrubs | ||
| Nuphar lutea ssp. pumila (=microphylla) | Small Yellow Water-lily | Forbs and Sub-Shrubs | ||
| Nymphaea odorata | American White Water-lily | Forbs and Sub-Shrubs | ||
| Osmunda (=Osmundastrum) cinnamomea | Cinnamon Fern | Forbs and Sub-Shrubs | ||
| Osmunda claytoniana | Interrupted Fern | Forbs and Sub-Shrubs | ||
| Petasites frigidus var. palmatus | Palmate Sweet Coltsfoot | Forbs and Sub-Shrubs | ||
| Phegopteris connectilis | Long Beech Fern | Forbs and Sub-Shrubs | ||
| Ranunculus lapponicus | Lapland Buttercup | Forbs and Sub-Shrubs | ||
| Rubus pubescens | Dwarf Raspberry/Dewberry | Forbs and Sub-Shrubs | ||
| Sagittaria latifolia | Broadleaf Arrowhead | Forbs and Sub-Shrubs | ||
| Sarracenia purpurea | Purple Pitcherplant | Forbs and Sub-Shrubs | ||
| Scheuchzeria palustris | Rannoch-rush/Pod-grass | Forbs and Sub-Shrubs | ||
| Solidago uliginosa | Bog Goldenrod | Forbs and Sub-Shrubs | ||
| Streptopus lanceolatus | Twisted Stalk | Forbs and Sub-Shrubs | ||
| Symphyotrichum boreale | Northern Bog Aster | Forbs and Sub-Shrubs | ||
| Symphyotrichum lateriflorum | Calico Aster | Forbs and Sub-Shrubs | ||
| Thelypteris palustris | Eastern Marsh Fern | Forbs and Sub-Shrubs | ||
| Triadenum fraseri | Fraser’s Marsh St. Johnswort | Forbs and Sub-Shrubs | ||
| Trientalis (=Lysimachia) borealis | Starflower | Forbs and Sub-Shrubs | ||
| Vaccinium oxycoccos | Small Cranberry | Forbs and Sub-Shrubs | ||
| Vaccinium vitis-idaea | Lingonberry | Forbs and Sub-Shrubs | ||
| Viola sp. | Violet species | Forbs and Sub-Shrubs |
Common Animal Species
| Scientific Name | Common Name | Category | At Risk | Notes |
|---|---|---|---|---|
A moose was observed along the North River in 2013 (Ethan Perry, pers. observation). |
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Eighty-three bird species have been recorded from the Big Lake-Seven Beaver RNA. |