Alnus incana Shrubland Alliance
Mountain alder thicket
Mountain alder thicket
USDA Ecological Section Map
Summary Information
- Primary Life FormShrub
- Elevation1200-2925 m
- State RarityS3
- Global RarityG4
- DistributionCAN: BC, MB, NB, NS, ON, PE, QC. USA: CA, CO, CT, IA, ID, IL, IN, MA, ME, MI, MN, MT, ND, NH, NJ, NM, NV, NY, OH, OR, PA, RI, UT, VT, WA, WI, WV, WY. Mexico (NatureServe)
- Endemic to CaliforniaNo
- Endemic to California Floristic Province and DesertsNo
- Date Added1995/11/01
Characteristic Species
Alnus incana is dominant or co-dominant in the shrub canopy with Acer glabrum, Cornus sericea, Salix jepsonii, Salix lemmonii, Salix melanopsis, Salix planifolia, Salix prolixa and Salix scouleriana. Emergent trees may be present at low cover, including Abies concolor, Pinus contorta ssp. murrayana, Pinus jeffreyi, Pinus ponderosa, Populus spp. or Salix spp.
Vegetation Layers
Shrubs < 10 m; canopy is intermittent to continuous. Herbaceous layer is variable and usually includes forbs, ferns, and grasses.
Membership Rules
- Alnus incana > 25% absolute cover in the small tree layer, where it usually dominates (Manning and Padgett 1995).
- Alnus incana > 5% absolute cover in the shrub layer where it dominates (Potter 2005).
Habitats
Montane streamsides, seeps, springs, and pond and lake margins. The USFWS Wetland Inventory (1996 national list) recognizes Alnus incana spp. tenuifolia as an OBL+ plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | Montane wetland shrub habitat, Mountain alder series |
| NVCS (2009) | Alnus incana seasonally flooded shrubland alliance, Alnus incana temporarily flooded shrubland alliance |
| Calveg | Riparian mixed shrub, Mountain alder |
| Holland | Montane riparian scrub |
| Munz | Not treated |
| WHR | Montane riparian |
| CDFW CA Code | 63.210.00 |
National Vegetation Classification Hierarchy
| Formation Class | Mesomorphic Tree Vegetation (Forest and Woodland) |
| Formation Subclass | Temperate Forest |
| Formation | Temperate Flooded and Swamp Forest |
| Division | Western North America Flooded and Swamp Forest |
| Macro Group | Western Cordilleran montane-boreal riparian scrub |
| Group | Western North American montane-subalpine riparian scrub |
Remarks
Alnus incana is a deciduous, multi-stemmed shrub or small tree that attains a height of 9 m and an age of about 100 years. Plants produce abundant seed, which is dispersed during fall and winter, but seed viability can be quite low (5%). Seeds require no treatment to break dormancy. Seedling establishment is best on exposed mineral soil. Their flexible stems are well adapted to frequent disturbance. Plants fix atmospheric nitrogen through a symbiotic relationship with bacteria (Uchytil 1989b).
Alnus incana is a circumboreal shrub involving three subspecies: A. incana ssp. incana in Europe and Asia, ssp. rugosa in the Lake States and New England, and ssp. tenuifolia in the western mountains of the United States (Brayshaw 1976). The ecology of the subspecies is similar, and both North American subspecies are included in the same alliance (NatureServe 2007a).
Stands in California are restricted to montane riparian thickets in the northern half of the state. They typically occupy relatively cool and shady settings along small to mid-size streams and rivulets, seeps and springs, and meadow complexes. There is little overlap with Salix-dominated alliances because the latter typically occupy warmer, sunnier exposures or montane zones in more southerly latitudes. A. incana meets the other shrubby alder, A. viridis, in the Klamath Mountains. Seasonally flooded stream banks provide seedbeds for establishment of A. incana stands, and stands may be transitional to riparian hardwood- or conifer-dominated woodlands or forests (Uchytil 1989b, Potter 2005).
Alnus incana is a circumboreal shrub involving three subspecies: A. incana ssp. incana in Europe and Asia, ssp. rugosa in the Lake States and New England, and ssp. tenuifolia in the western mountains of the United States (Brayshaw 1976). The ecology of the subspecies is similar, and both North American subspecies are included in the same alliance (NatureServe 2007a).
Stands in California are restricted to montane riparian thickets in the northern half of the state. They typically occupy relatively cool and shady settings along small to mid-size streams and rivulets, seeps and springs, and meadow complexes. There is little overlap with Salix-dominated alliances because the latter typically occupy warmer, sunnier exposures or montane zones in more southerly latitudes. A. incana meets the other shrubby alder, A. viridis, in the Klamath Mountains. Seasonally flooded stream banks provide seedbeds for establishment of A. incana stands, and stands may be transitional to riparian hardwood- or conifer-dominated woodlands or forests (Uchytil 1989b, Potter 2005).
Life History Traits of the Principal Species
| Alnus incana | |
|---|---|
| Life forms | Shrub; winter deciduous |
| Seed storage | Soil? |
| Seed longevity | Medium? |
| Mode of dispersal | Wind; water/hydrological |
| Germination agents | None |
| Mode of sprouting | Underground structures |
| Survivability after fire/disturbance | Fire-hardy; low flammability; high sprouter |
| Disturbance-stimulated flowering | No |
| Reproductive range | Unknown |
| Recruitment | High |
| Regional variation | Low |
Fire Characteristics
Stands are primarily disturbed by fluvial processes rather than fire. The species may respond to fire by sprouting from the root crown after fire and colonizing from numerous wind- and water-dispersed seeds (Uchytil 1989b). If fires do occur in the alliance, they have less than half the median fire return interval of surrounding forests.
| Fire return interval | Depends on neighboring alliances. Half the median frequency of surrounding forests |
| Seasonality | Summer-fall |
| Size/extent | Small to medium |
| Complexity | High |
| Intensity | Low to high |
| Severity | Low to high |
| Type | Surface-crown fire |
| Regional knowledge | Klamath, Cascade, and North Coast ranges |
Regional Status
- Klamath Mountains (M261Ad, Ag, Aj, An-p, As-u). Stands occur more commonly in the central and eastern subsections surrounding streams and adjacent to wet meadows as far west as the southern border along the higher portions of South Fork Mountain. In much of the western Klamath Mountains, the alliance is largely replaced by A. viridis. Both alliances occur in the central portion, where A. incana tends to be in shady sites.
- Northern California Coast Ranges (M261Ba). Meadow and streamside stands occur in the Yolla Bolly Mountains south to Snow Mountain; these are usually on northern exposures. Stands are described at Doll Basin RNA (Cheng 2004) and generally for the Yolla Bolly Mountains (Keeler-Wolf and Keeler-Wolf 1974).
- Sierra Nevada (M261Eb, Ed-e, Eg-h, Ej-o, Eq, Et). Many stands along middle elevation streamsides (Potter 2005) are transitional to flood-prone areas and in avalanche chutes in the Abies magnifica, A. concolor, and Pinus contorta ssp. murrayana zones in the section. The alliance exists as far south as the Stanislaus River drainage, but apparently does not occur as stands in Yosemite National Park. Stands occur in the upper San Joaquin River Drainage in Devils Postpile National Monument (S. Haultain, pers. comm. 2004). The most southerly occurrence is in Fresno Co. Stands are described at Clark Fork cRNA, Grass Lake RNA, Lyon Peak/Needle Lake RNA, Moses Mountain RNA, Mount Pleasant RNA, Mud Lake RNA, and Onion Creek study area (Cheng 2004).
- Southern Cascades (M261Df, Dm). Meadow and stream bank stands occur commonly in the A. magnifica and A. concolor forest zones from Mount Shasta to Mount Lassen, including as far east as Antelope Creek Lakes, Green Island Lake, and Soda Ridge rRNAs (Cheng 2004).
Management Considerations
Alnus incana with its nitrogen-fixing bacteria provides a nutrient supply to streams and ponds. It is not an aggressive colonizer in California, but it helps maintain stream bank stability and prevents soil loss on the steep forested hillsides on which it commonly occurs.
Associations
- Alnus incana [2], [4]
- Alnus incana / bench [1]
- Alnus incana / Glyceria elata [3]
References
- [1] Manning, M.E.;Padgett, W.G. 1995
- [2] Potter, D.A. 2005
- [3] Smith, S. 1998b
- [4] Ratchford, J.;Boul, R.;Keeler-Wolf ,T.;Evens, J. 2024b (in progress)
- Brayshaw, T.C. 1976
- Hansen, P.L.;Chadde, S.W.;Pfister, R.D. 1988
- Reid, M.S.;Schulz, K.A.;Cormer, P.J.;Schindel, M.H.;Culver, D.R.;Sarr, D.A.;Damm, M.C. 1999
- Uchytil, R.J. 1989b