Alnus incana

Speckled Alder

Speckled Alder, Bald Eagle Lake, BWCA

Speckled Alder, Bald Eagle Lake, BWCA
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


Name:

  • Alnus, from the Latin for the alder
  • incana, from the Latin, "grey"
  • Speckled, a reference to the white lenticels (spongy openings for gas exchange) which cover the bark.
  • Other common names include Grey Alder, Hazel Alder, Hoary Alder, European Speckled Alder, Mountain Alder, Tag Alder, Rough Alder, Graol (Nor), Gråal (Swe), Harmaaleppä (Fin), Verne (Qué), Aulne Blanch Atre (Qué), Gráelri (Is).

Taxonomy:

  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Hamamelididae
        • Order Fagales
          • Family Betulaceae, the Birches
            • Genus Alnus, the Alders
  • Taxonomic Serial Number: 181887
  • Also known as Alnus rugosa, Betula alnus (rugosa), Betula alnus, Alnus incana ssp. rugosa, Alnus americana, Alnus serrulata

Description:

  • A tall, deciduous, thicket-forming, rhizomatous shrub or small tree, to 20' tall.
  • Leaves dull dark green above, light yellow-green and finely hairy underneath, ovate to elliptic in shape with doubly toothed and shallowly lobed edges; 2"-5" long, 1¼" -2¾" wide, with ¼" -1" leafstalks.
  • Stem
    • Twigs reddish-brown, moderately slende; buds contain two or three bud scales.
    • Bark thin and smooth with conspicuous orange lenticils, hence the name.
  • Roots Nitrogen fixing
  • Flowers
    • Staminate (male) catkins 1½"-3½" long;
    • Pistillate (female) catkins sessile, cylindrical, and only 3/16" long.
  • Fruit an oval, 5/8"x5/16", winged nutlet borne in egg-shaped cones. Nutlets flat, slightly winged, about 3mm across.

Identification:

  • Identifiable as an Alder/Hazel by its coarse, toothed leaves and shrubby growth form
  • Distinguished from other Alder/Hazel with some difficulty
  • Field Marks

Distribution:

  • Most common in the region surrounding the Great Lakes and the St. Lawrence, including east-cental Canada, the Maritimes, and the Northeast and Lake States.

Habitat:

  • Moist lowlands, frequently bordering streams and lakes, common in swamps and the older zones of bogs. Frequently found in riparian, bog, and nutrient-rich swamp communities. Often dominates Black Spruce (Picea mariana), Jack Pine (Pinus banksiana), Tamarack (Larix laricina), White Cedar (Thuja occidentalis), and Birch/Aspen understories on nutrient-rich, mesic sites. Where range overlaps that of its close relative, Green Alder (Alnus crispa), it tends to be found on lowland sites and Green Alder on upland sites.
  • Soils: Adapts to a variety of soils provided they are moist and nutient-rich. Grows in mucky soils, which are relatively shallow over glacial till or deep over lacustrine peat. Also grows in sandy loams, grey forest soils, minerotropic peatlands, alluvial soils, and ericaceous bogs, on both poorly drained and well-drained sites. Soil pH varies between 4.8 and 7.7
  • Shade tolerance: Although a common understory shrub, grows more vigorously in full sunlight of forest openings and sparsely stocked stands. Decribed as shade intolerant to intermediately shade intolerant.
  • An early succession species that quickly invades forest openings created by fire and/or logging. An early colonizer of gaps in wetland forests. Exposure of the mineral soil creates optimal seedbeds and speeds invasion of a site. Historically, Speckled Alder may have been an early colonizer of recently deglaciated areas in North America. Eventually gives way to conifers on most sites.
  • Sensitive to prolonged flooding above the root crown; may be sensitive to acid precipitation.

Fire:

  • Survives fire through persistent root crowns. Sprouting occurs from underground stems at or within 2" of the soil surface. An able competitor, it can outcompete some tree species and delay or arrest succesion.
  • Fire kills the aboveground portion of the plant. Root crowns in the mineral soil burn only under the most severe conditions, but they can be killed by the heat generated during a fire. Severe fires that remove the organic layer and expose and char root crowns can completely eliminate sprouting.
  • Open-growing alders more vulnerable to fire than thicket-growing alders because very little understory fuel accumulates in alder thickets.
  • Following mild fires, sprouts quickly from persistent root crowns. Severe fires delay alder regeneration. Speckled Alder in the Lake States reaches peak abundance 10 years after fire.
  • Where present, fire and most logging practices will favor it over competing species. Rebounds quickly after overstory removal and readily invades disturbed sites. Fire suppression favors the continued growth of alder and other tall shrubs in boreal forest understories (typically fir, spruce, and cedar). Longer fire intervals may encourage the expansion of alder thickets at the expense of other forest types.

Associates:

  • Trees: Balsam fir (Abies balsamea), Red Maple (Acer rubrum), Paper Birch (Betula papyrifera), Tamarack (Larix laricina), Black Spruce (Picea mariana), Jack Pine (Pinus banksiana), Balsam Poplar (Populus balsamifera), Bigtooth Aspen (Populus grandidentata), Quaking Aspen (Populus tremuloides), White Cedar (Thuja occidentalis)
  • Shrubs:
  • Herbs: Cinnamon Fern (Osmunda cinnamonea), Sedges (Carex spp.)
  • Ground Covers: Sphagnum mosses (Sphagnum spp.)
  • Fungi: All of the alders associate symbiotically with species of the actinomycete Frankia , leading to the formation of nodules on the roots of the plants and the fixation of atmospheric nitrogen.
  • Mammals:
    • Winter cover for Snowshoe Hare.
    • Moose, muskrats, beavers, cottontail rabbits, and snow-shoe hares feed on the twigs and foliage. Low preference white-tailed deer browse, avoided by moose in the Lake Superior region.
    • Thickets provide hiding cover to moose and white-tailed deer.
    • Beavers build dams and lodges with speckled alder.
  • Birds:
    • Songbirds, including American Goldfinch, Pine Siskin, and Redpoll feed on the seeds.
    • Woodcock and grouse eat the buds and catkins.
    • Thickets provide drumming sites to woodcock and grouse.

History:

  • Ojibwe used with Bloodroot, Wild Plum, and Red Osier Dogwood (Cornus sericea) to make a scarlet dye for porcupine quill embroidery.

Uses:

  • Because of its coarse, shrubby growth habit the wood has no commercial value; used locally for fuel.
  • Supports symbiotic, nitrogen-fixing bacteria in root nodules.

Reproduction:

  • Reproduces by seed and vegetatively by rhizomes.
  • Sexual reproduction: Wind pollinated. Flowers appear late in summer and become functional the following May or April. Winged seeds ripen during late August and September and are dispersed by wind through April. Germination usually requires exposed mineral soil, which may need to be saturated.
  • Vegetative reproduction, rather than seedlings, provides most of the new stems in established stands, primarily through sprouting; but also through layering, suckers, and underground stems. Sprouting is independent of stem damage. Clonal, often forming impenetrable thickets. With conifer competition, local distribution is more diffuse. Release after removal of overstory competition is immediate. Isolated clumps expand radially and coalesce.
  • Forms large colonies from rhizomes and by layering
  • Male catkins and female flowers on same plant

Propagation:

  • Seed and seedling stock seldom available commercially. Seed are easily shaken from dried cones collected in September and October. In the nursery, fresh seed should be broadcast and drilled into washed sand or a sand-humus mixture. Seedbeds should be mulched for overwinter protection with mulch removed prior to germination in the spring.
  • Spring planting requires stratification in moist sand or vermiculite for 60 to 90 days. Seedbeds should be kept moist and shaded until late in the summer. Two or three year-old seedlings should be used for field planting. Site preparation requires sod layer removal to prevent herbaceous competition.

Cultivation:

  • Hardy to USDA Zone 2 (average minimum annual temperature -50ºF)
  • Cultural Requirements
    • Full sun
    • Moist, nutrient-rich soil
  • Good choice for disturbed site rehabilitation and providing streambank stability and erosion control.
  • The presence of nitrogen-fixing, symbiotic bacteria in its root nodules makes speckled alder valuable for soil conditioning.
  • A bit coarse for most home landscapes.

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Last updated on 29 August, 2004