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    Author(s): Constance A. Harrington
    Date: 2006
    Source: In: Red alder—a state of knowledge: 21-43
    Publication Series: General Technical Report (GTR)
    Station: Pacific Northwest Research Station
    PDF: Download Publication  (2.97 MB)


    Red alder is the most common hardwood in the Pacific Northwest with a range stretching from coastal southeast Alaska to southern California and east to isolated populations in Idaho. Soil moisture during the growing season influences where it grows and its growth rates; it can tolerate poor drainage but not droughty, hot sites. Due to its tolerance of wet soil conditions, alder is common in riparian areas. Alder can be injured by spring and fall frosts and is not found at elevations above 11O0 m anywhere in its range. The species produces small, very light seeds that disperse over long distances; it is favored by disturbance and often increases in abundance after logging or burning. Alder establishment via seed is not assured, however, as drought and heat injury, pathogens, animals and other factors often destroy seedlings. Alder has nitrogen-fixing nodules on its roots that directly and indirectly increase nitrogen in forest ecosystems. Alder usually has a spreading fibrous root system when young and can root deeply if soil aeration is not limiting. When grown in dense stands its shade intolerance results in rapid mortality of shaded stems and lower branches. It is a relatively short-lived, intolerant pioneer with rapid juvenile growth. This pattern of height growth—very rapid when young and slowing quickly at a relatively young age—means that if thinning is delayed, alder can not rapidly build crown and increase in diameter growth. Although alder wood stains and decays rapidly after death, live trees compartmentalize decay very efficiently, and pruning and thinning are feasible operations. Stem rots do not result in high volumes of damage overall but can be locally important; ring shake can also be a serious problem in some stands. Insects and diseases are not generally a problem in young stands although insect defoliators, Nectria cankers, and alder bark beetles can cause problems. Meadow mice, voles, and beaver can also hinder stand establishment in some areas. Deer or elk may rub small alder saplings during the fall with their antlers but do not usually browse its leaves and twigs. Sapsucker damage is sporadic, but if stems are repeatedly damaged, their future log value will be greatly reduced. Mortality and top damage have been observed after ice or early snowstorms. Red alder is now being managed for a wider range of objectives and on many more sites than in the past; this is due to recent increases in wood value of alder relative to other species as well as its ability to fill specialized niches (e.g., add nitrogen to forest ecosystems, immunity to laminated root rot) and produce sawlogs on relatively short rotations. Management experience with the species, however, is still limited to a fairly narrow range of sites and management scenarios. Thus, information on the biology and ecology of the species should help guide managers until more direct experience is available.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Harrington, Constance A. 2006. Biology and ecology of red alder. In: Red alder—a state of knowledge: 21-43


    Alnus rubra, biology, ecology, damaging agents, growth, red alder, regeneration

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