Betula occidentalis Shrubland Alliance
Water birch thicket
Water birch thicket
USDA Ecological Section Map
Summary Information
- Primary Life FormShrub
- Elevation600-2500 m
- State RarityS3
- Global RarityG4
- DistributionCAN: AB. USA: CA, CO, ID, MT, NM, NV, OR, SD, UT, WA, WY (NatureServe)
- Endemic to CaliforniaNo
- Endemic to California Floristic Province and DesertsNo
- Date Added1995/11/01
Characteristic Species
Betula occidentalis is dominant or co-dominant in the tall shrub or low tree canopy with Acer negundo, Alnus spp., Artemisia tridentata ssp. vaseyana, Cornus sericea, Pinus jeffreyi, Pinus monophylla, Populus fremontii, Populus tremuloides, Populus trichocarpa, Prunus virginiana, Rosa woodsii and Salix spp. If B. occidentalis is shrubby, emergent trees may be present at low cover.
Vegetation Layers
Otherwise, low trees < 30 m; canopy is intermittent to continuous. Shrubs are typically sparse if the birch forms a low tree canopy. Herbaceous layer is sparse.
Membership Rules
- Betula occidentalis > 25% cover in the tall shrub or short tree canopy (NatureServe 2007).
- Betula occidentalis > 30% cover in the shrub layer (Boul et al. 2021b).
- Betula occidentalis > 50% relative cover in the shrub layer or > 30% relative cover with Salix spp. (Reyes et al. 2020a).
Habitats
Intermittently, temporarily saturated stream banks, alluvial terraces, and seeps. Substrates are typically alluvial and range from fairly shallow, finely textured to gravelly and bouldery sands and loams. The USFWS Wetland Inventory (2018 national list) recognizes Betula occidentalis as a FACW plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | Water birch series |
| NVCS (2009) | Betula occidentalis intermittently flooded shrubland alliance, Betula occidentalis seasonally flooded shrubland alliance, Betula occidentalis temporarily flooded shrubland alliance |
| Calveg | Water birch, Riparian mixed shrub, Riparian mixed hardwood, Cottonwood-Alder, Willow |
| Holland | Modoc-Great Basin riparian forest, Modoc-Great Basin riparian scrub |
| Munz | Not treated |
| WHR | Montane riparian |
| CDFW CA Code | 63.610.00 |
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 | Great Basin montane riparian scrub |
Remarks
Betula occidentalis usually has many spreading trunks and takes the shape of a tall shrub or short tree. It produces many wind-dispersed seeds by early summer. Seedling establishment occurs in shaded areas with sufficient soil water (Uchytil 1989f). B. occidentalis can form dense, closed tree or shrub-like canopies and as a result the herbaceous understory is generally limited and sparse.
Betula occidentalis produces distinct riparian corridors along streams, primarily in transmontane California, but regional descriptions commonly include these stands in broadly defined riparian types. This alliance generally develops along small creeks, well-defined incised channels, steep stream banks, and alluvial terraces where B. occidentalis can stabilize the substrate with its deep roots. Stands are also found on wider stream benches and floodplains, or on hillside seeps in mountains and foothills (NatureServe 2019). Stands of B. occidentalis have environmental conditions similar to Populus spp. and Salix spp. alliances.
The alliance ranges throughout the West.
Betula occidentalis produces distinct riparian corridors along streams, primarily in transmontane California, but regional descriptions commonly include these stands in broadly defined riparian types. This alliance generally develops along small creeks, well-defined incised channels, steep stream banks, and alluvial terraces where B. occidentalis can stabilize the substrate with its deep roots. Stands are also found on wider stream benches and floodplains, or on hillside seeps in mountains and foothills (NatureServe 2019). Stands of B. occidentalis have environmental conditions similar to Populus spp. and Salix spp. alliances.
The alliance ranges throughout the West.
Life History Traits of the Principal Species
| Betula occidentalis | |
|---|---|
| Life forms | Shrub; tree; winter deciduous |
| Seed storage | Transient |
| Seed longevity | Short; medium |
| Mode of dispersal | Water/hydrological; wind |
| Germination agents | None |
| Mode of sprouting | Underground structures |
| Survivability after fire/disturbance | Fire-hardy; high sprouter |
| Disturbance-stimulated flowering | No |
| Reproductive range | Short-lived |
| Recruitment | High |
| Regional variation | Low |
Fire Characteristics
Hydrological processes primarily influence this alliance. Fires that do occur spread largely from adjacent burning vegetation. Stems and trunks are easily top-killed by fire, but plants sprout from basal buds.
| Fire return interval | Long (rarely burns; fire regime depends on adjacent alliances) |
| Seasonality | Summer-early fall |
| Size/extent | Small; up to or beyond stand size (depends on landscape) |
| Complexity | High |
| Intensity | Low |
| Severity | Low |
| Type | Surface fire |
| Regional knowledge | Klamath, Cascade, Modoc Plateau |
Regional Status
- Klamath Mountains (M261Ah, Aj, Al). Stands occur in seeps and along streams surrounding Scott Valley and in the Scott Mountains.
- Modoc Plateau (M261Gf). Stands occur on the eastern escarpment of the Warner Mountains. The few stands in the southern Warners have similar settings to those along the Sierra Nevada escarpment.
- Mojave Desert (322Aa). Desert scrublands surround the few stands in foothill drainages of the lower Owens Valley.
- Mono (341Dh, Dj, Dl). The Sierra Nevada stands continue into this section in the Mammoth area at Convict and McGee creeks. They also occur in the White Mountains.
- Northwestern Basin and Range (342Bd). Stands present along creeks at the northern end of the subsection, on the eastern slopes of the Warner Mountains (Menke et al. 2021).
- Sierra Nevada (M261Ej, Eo, Er). Most stands exist along the eastern escarpment from Mammoth south to the vicinity of Olancha. They line most of the major permanent streams and range from stands surrounded by coniferous vegetation to high desert shrublands. They are rare along the eastern slope of Babbitt Peak. Stands north of Reno are adjacent to Quercus kelloggii stands. Harris (1988) denotes eastside locations of stands in steep, narrow valleys on glacial till.
- Southern Cascades (M261Dh). Stands are local in riparian areas at lower elevations.
Management Considerations
Betula occidentalis often forms dense, pure stands that provide cover for wildlife (Uchytil 1989f). They require permanent flowing water during the growing season.
Formerly extensive stands along the eastern Sierra Nevada and adjacent Owens Valley area have been reduced as a result of water export to Los Angeles, California (S. Manning, pers. Comm. 2006).
Betula occidentalis is highly adapted to most forms of disturbance, but heavy grazing eliminates native graminoids that are typically replaced by introduced species in the understory (NatureServe 2019).
Associations
- Betula occidentalis / Mesic graminoids [3]
- Betula occidentalis / Salix spp. [1], [2]
References
- [1] Harris, R.R. 1988
- [2] Reyes, E.;Evens, J.;Glass, A.;Sikes, K.;Keeler-Wolf., T.;Winitsky, S.;Johnson, D.;Menke, J.;Hepburn, A. 2020a
- [3] NatureServe, 2014+
- Boul, R.;Keeler-Wolf, T.;Ratchford, J.;Haynes, T.;Hickson, D.;Yacoub, R.;Harbert, B.;Evens, J. 2021b
- Holstein, G. 1984
- Manning, M.E.;Padgett, W.G. 1995
- Uchytil, R.J. 1989f