Red alder

Red alder (Dr) - Alnus rubra

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Geographic range and ecological amplitudes


Red alder is a medium-sized (<40m tall), deciduous broad-leaved tree at maturity with a narrow rounded crown, straight, slightly tapered stem, and smooth, light gray bark. Red alder wood is moderately dense, and uniformly textured. It is used for firewood and specialty products.

Geographic range 

Geographic element:
Western North American/Pacific

Distribution in Western North America:
north, central, and south in the Pacific region

Ecological amplitudes 

Climatic amplitude:

(cool temperate) - cool mesothermal

Orographic amplitude:

submontane - montane

Occurrence in biogeoclimatic zones:

Edaphic amplitude

Red alder

Range of soil moisture regimes:
(moderately dry) - slightly dry - fresh - moist - very moist - wet

Range of soil nutrient regimes:
(very poor) - poor - medium - rich - very rich

Red alder has high requirements for calcium, magnesium, phosphorus and potassium; however, after fire, it can become established, like any other alder species, in nitrogen-poor soils because of a symbiotic relationship with a nitrogen-fixing actinomycete. Thus, the presence of red alder will result 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. Nitrogen fixed in the nodules is added to the soil in four ways: direct excretion from living roots or nodules, decomposition of dead roots or nodules, leaching from foliage, and decomposition of nitrogen-rich litter. Maximum annual fixation rates of 320kg/ha have been reported.

Tolerances and damaging agents

Root system characteristics

Red alder develops an extensive, fibrous root system, with root nodules that fix atmospheric nitrogen. The nodules are a symbiotic association between the tree and an actinomycete (Frankia ssp.). Nodulation occurs soon after seed germination. Roots are associated with ecto- and endo-mycorrhizae.


Tolerance to Tolerance class Comments
low light L a very intolerant, exposure-requiring species
frost L not a major concern in mesothermal climates
heat L infrequent on insolated sites
water deficit L sheds leaves during acute summer water deficits
water surplus H tolerates wet sites, flooding, and sites with a strongly fluctuating water table well
nutrient (mainly N) deficiency H infrequent in acid, very poor soils


Damaging agents

Damaging agent Resistance class Comments
snow L ice storm damage quite frequent
wind M high winds will break the boles rather than uproot trees


  Risk class  
fire L fire risk in red alder stands is low
insect L not a major concern
fungi L not a major concern

Associated tree species and successional role

In British Columbia, red alder grows in even-aged, pure stands and, in later successional stages, with shade-tolerant conifers. It is a pioneer species (primary succession) on floodplains and present in early and intermediate stages of secondary succession on upland sites.

Associated tree species
tree species
Occurance class Major area of occurance
western hemlock M CWH
sitka spruce M mainly in hypermaritime CWH
black cottonwood M floodplains in southern coastal B.C
western redcedar M CDF and CWH
grand fir L southern coastal B.C
bigleaf maple L southern coastal B.C


Silvical characteristics

Characteristic Interpretive class Comments
reproduction capacity H reproduces vegetatively from stump sprouts; the minimum age for seed crops is as low as 3 years
seed dissemination capacity H dispersed by wind and water
potential for natural regeneration in low light L practically nil; a very shade-intolerant and exposure-requiring species
potential for natural regeneration in the open H regenerates nearly exclusively on mineral soil; direct seeding yields good results
potential initial growth rate (<5 years) H exceptionally rapid (>1m in the first growing season)
response of advance regeneration to release na advance regeneration does not develop in the absence of adequate light and seedbeds
self-pruning capacity in dense stands H provided initial stand density is high
crown spatial requirements M varies with density
light conditions beneath closed-canopy, mature stands H associated with well-developed understory vegetation
potential productivity H site index (50 yr @ bh) close to 40m on productive sites
longevity L maturing at about 60 years, rarely >100 years old


Genetics and notes


Population differences in morphological and physiological characters have been demonstrated in trials (Dang et al. 1994), but no races and natural hybrids have been described.


Red alder produces in a short time (about 30 years or less) high yields of wood. Considering its productivity, easy regeneration (prolific annual seed crops), and low risk of being affected by damaging agents, it is a suitable species for intensive management on some coastal sites, especially those where the establishment of conifers is fraught with difficulties (for example, on riparian sites).

It is also suitable as a nurse crop species on nitrogen-poor sites (although the more shrubby and shade-tolerant Sitka alder may be more appropriate) and severely disturbed sites (landslides, landings, etc.). It has been suggested as a nurse species for Sitka spruce, as its shade and visual diversion will deter spruce weevil. More detailed silvics information is given by:

Harrington, C.A. 1990. Alnus rubra. Pp. 117-123 in R.M. Burns and B.H. Honkala (technical coordinators) Silvics of North America, Vol. 2. Agri. Handbook 654, USDA For. Serv., Washington, D.C.

Peterson, E.B., G.R. Ahren, and N.M. Peterson. 1996. Red alder manager''''s handbook for British Columbia. FRDA Report 240, B.C. Min. For., Victoria, B.C. 124 pp.