Sitka alder (Alnus alnobetula ssp. sinuata) is a hardy shrub that is found at higher elevations in the subalpine on Vancouver Island, British Columbia. A reliable place to see this plant is in Strathcona Provincial Park where Sitka Alder grows in several accessible places on the loop trail that follows the shoreline of Lake Helen Mackenzie. The bushy shrub is a common, but often overlooked member, of this subalpine environment. Once you know its identifying features it is easily recognizable.
Identifying Features of Sitka Alder
Sitka alder is a deciduous shrub or small tree, typically under 5 metres tall, often growing in dense, tangled thickets. Its form and habitat can help distinguish it from its better-known lowland cousin, the red alder (Alnus rubra), which reaches up to 25 metres in height and prefers moist, lower-elevation riparian forests.
The leaves of the Sitka alder are broadly oval, and have a somewhat rounded base and pointed tip. The upper surface of the leaf is dark green and shiny while the underside of the leaf is slightly sticky. Margin edges are wavy lobed (sinuate). In addition, the edges of the leaf are noticeably double saw-toothed. In contrast, the leaves of red alder lack a strongly toothed edge.
Like other alders, Sitka alder is monoecious, bearing both male and female catkins. The photograph above shows both the large male catkins and smaller female catkins (strobiles). In spring and early summer, male catkins—long, drooping, yellow-green structures—unfurl from leaf axils. Female catkins are much smaller and upright, located above the male catkins. These develop into hard, woody cones that persist through winter, releasing tiny winged seeds in the fall. The persistent cone-like fruits, along with the shrubby stature and subalpine habitat, are useful features to confirm an identification.
Like other members of birch family (Betulaceae), the catkins produce a prolific amount of pollen. A noticeable thick skim of yellow pollen floated on the surface of the water of Lake Helen Mackenzie near where shrubs were growing on the shoreline.
Comparing Sitka Alder to Red Alder
Though both are native to British Columbia, Sitka alder and red alder differ in several key ways:
| Feature | Sitka Alder | Red Alder |
|---|---|---|
| Height | Shrub to small tree (up to 5m) | Medium to large tree (up to 25m) |
| Leaves | Glossy, sharply toothed, deeply veined | Duller, more rounded, rolled-under edges |
| Habitat | Subalpine slopes, avalanche tracks, wet meadows, shorelines | Coastal lowland forests, riparian zones, recently cleared land |
| Bark | Grayish, thin, often with lichens | Whitish-gray, often with moss or lichen |
| Growth | Clonal thickets, often multi-stemmed | Single-trunked in forest settings |
Subalpine Adaptations and Ecosystem Roles
Sitka alder is well-adapted to harsh, high-elevation environments. Its shrubby form allows it to resist damage from heavy snow loads, and its early leaf-out and rapid growth capitalize on the brief subalpine growing season. It also plays an important ecological role in stabilizing slopes, enriching soils, and creating dense microhabitats for subalpine wildlife like birds and small mammals. Insects also utilize the pollen created by the catkins, assisting in pollination in the process. Hoverflies seem to be particularly attracted to the catkins!
As alder thickets mature, they improve soil fertility, allowing conifers and other late-successional species to establish. Sitka Alder is particularly good at colonizing disturbed and rocky subalpine soils making it a key pioneer species in early successional environments. In these locations it also acts as a stabilizer and reduces erosion.
Easy to Miss, Easy to Appreciate
With the magnificent view of Lake Helen Mackenzie and beautiful subalpine flowers competing for your attention it is easy to miss this unassuming shrub on the shore of the lake and other places in the park. Watch for the distinctive leaves—they’ll look like the red alder leaves that you might be familiar with at lower elevation but they’ll be just a bit different. When you find this subalpine alder, stop and appreciate its resilience. Take the time to contemplate the important pioneering role it plays in this ever changing ecosystem.
Synonyms and Alternate Names
Alnus alnobetula ssp sinuata has a number of synonyms including Alnus crispa ssp sinuata and Alnus viridis ssp sinuata. A list of additional names and taxonomy is at Oregon State University: College of Agricultural Sciences.
Thank you for this informative work!