Mountain alder (Xc1) - Alnus tenuifolia
Mountain alder is a tall shrub to small-, rarely medium-sized (<15 m), deciduous broad-leaved tree, at maturity with a clumped, crooked stem and smooth grey or reddish-grey bark with horizontal orange lenticels. Mountain alder is a much less aggressive species than the related European grey alder [Alnus incana (L.) Moench] with which it is joined by some taxonomists as ssp. tenuifolia (Nutt.) Breitung.
|Geographic Range||Geographic element:
Western North American/Pacific, Cordilleran, and marginally Central
Distribution in Western North America:
(north) in the Pacific region, north, central, and south in the Cordilleran region
subarctic - subalpine boreal - montane boreal - cool temperate
montane - subalpine
Occurrence in biogeoclimatic zones:
(lower SWB), (lower ESSF), (MS), BWBS, SBS, (SBPS), IDF, ICH
Range of soil moisture regimes:
(slightly dry) - fresh - moist - very moist - wet
Range of soil nutrient regimes:
(poor) - medium - rich - very rich; calciphytic, living in symbiosis with nitrogen-fixing Frankia spp.
The nutritional requirements of mountain alder are similar to those of red alder.
|Root System Characteristics||Mountain alder develops a fibrous root system with nodules that fix atmospheric nitrogen. The nodules are a symbiotic association between the tree and an actinomycete (Frankia spp.). Nodulation occurs soon after seed germination. Roots are associated with ecto- and endo-mycorrhizae.|
|Associated tree species and successional role||Mountain alder grows scattered in marginally forested, riparian and wetland ecosystems and in some areas forms dense thickets. It may be present as a pioneer species (primary succession) on floodplains; and occurs often in early and intermediate stages of secondary succession on floodplains and upland sites. As a moderately shade-tolerant tree, mountain alder maintains its presence in open-canopy riparian stands and wetlands.|
|Notes||Unlike red alder, mountain alder is not a potential timber crop species; however, it is a useful component of wetland ecosystems, and its presence on upland sites results in increases in both nitrogen content and its availability in the soil, along with increases of organic matter and soil acidity, and decreases in bulk density.
Another two shrub alders occur frequently in interior British Columbia across a wide range of sites: Sitka alder [Alnus sinuata (Regel) Rydb.] and green alder [Alnus viridis (Chaix) DC. in Lamb & DC.]. They are calciphytic and grow in symbiosis with nitrogen-fixing bacteria. Because both are moderately shade-tolerant, they are very suitable as soil-ameliorating nurse species in the understory of coniferous stands, especially on nitrogen-poor sites, and on landslides.
Sitka alder hybridizes with green alder. This interspecific breeding would be intraspecific if Sitka alder is interpreted only as a subspecies of green alder, i.e., Alnus viridis (Chaix) DC. in Lam. & DC. ssp. sinuata (Regel) Love & Love. The North American and North Asian race of the circumpolar green alder was described as Alnus viridis (Chaix) DC. in Lam. & DC. subsp. fruticosa (Ruprecht) Nyman.