Sitka alder
Alnus viridis (Chaix.) D.C.

Introduction

Sitka alder is an early successional deciduous shrub or, sometimes, a small tree. Plants often have multiple stems and may form dense thickets. Occasionally, plants may grow up to 12 m at lower elevations, but the species usually occurs at middle to high elevations. Sitka alder tolerates some shading as well as high water tables. Its capacity to symbiotically fix nitrogen enables the species to invade areas such as those with recently exposed mineral substrate from glaciers or avalanches (Uchytil 1989). Sitka alder has been used to stabilize soil on such slopes (Haeussler and Coates 1986) as well as stream banks. The species also provides cover for wildlife, nesting and foraging habitat for birds, and food for small animals and birds (Healy and Gill 1974). Because of its nitrogen-fixing capacity and its positive impact on leaf litter quality and soil fertility, Sitka alder can be used as a nurse crop for conifers (Haeussler and Coates 1986).

Sitka alder is distributed in the north and central Pacific and Cordilleran regions, from central Alaska and the Yukon Territory to north California and Montana. In British Columbia, it covers most of the province except the northeast (Little 1976).

Distribution and Protected Areas – from Hamann et.al. 2005

Conservation Status Summary – from Chourmouzis et.al. 2009

No in situ conservation concerns were identified for this species.

Reproduction

The seeds of Sitka alder are light and can travel long distances by wind and by water. The species mostly reproduces by seeding into disturbed habitats (Haeussler and Coates 1986). There is at least one seed crop every four years (Banerjee et al. 2001). Sitka alder also sprouts from the root collar or stump when damaged. Therefore it is considered a weed species, and management often involves killing the stumps to allow for conifer regeneration.

Genetic structure

Alnus viridis ssp. sinuata hybridizes with ssp. crispa where their ranges overlap (Brayshaw 1976).

Resource management and seed transfer

Benowicz et al. (2000a) analysed 28 populations covering the species’ range in British Columbia. They found large genetic differences among populations in fall and winter frost hardiness, dry weight, growth rate and germination parameters. There were clear geographical patterns related to latitude and distance from the coast. The differences are likely to be adaptive. Benowicz et al. (2000b) analysed the same sources for gas exchange parameters. Canonical correlation analysis revealed that populations from colder winters and shorter summers had higher maximum photosynthetic rates, implying an inverse relationship between leaf longevity and photosynthetic capacity. This information may help evaluate the impact of climate change on plant communities.