| Alnus rubra | |
|---|---|
 | |
| Red alder leaves | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fagales |
| Family: | Betulaceae |
| Genus: | Alnus |
| Subgenus: | Alnus subg.Alnus |
| Species: | A. rubra |
| Binomial name | |
| Alnus rubra | |
 | |
| Natural range ofAlnus rubra | |
| Synonyms[2] | |
| |
Alnus rubra, thered alder,[3][4]is adeciduousbroadleaf tree native to westernNorth America (Alaska,Yukon,British Columbia,Washington,Oregon,California,Idaho andMontana).[2][5][6]
Alnus rubra is the largest species ofalder in North America and one of the largest in the world, reaching heights of 20 to 30 metres (66 to 98 ft). The official tallest red alder (as of 1979) stands 32 m (105 ft) tall inClatsop County, Oregon (US).[7] The trunks range from 25 to 50 centimetres (10 to19+1⁄2 in) in diameter.[8] The bark is mottled, ashy-gray and smooth, often colonized by whitelichen andmoss.[8] Theleaves areovate,7 to 15 centimetres (2+3⁄4 to 6 in) long, with bluntly serrated edges and a distinct point at the end; the leaf margin is revolute, the very edge being curled under, a diagnostic character which distinguishes it from all other alders. Rather than turning yellow in autumn, its leaves darken in colour and wither before they are shed. The maleflowers are dangling reddishcatkins 10 to 15 cm (4 to 6 in) long in early spring. Female flowers occur in clusters of (3) 4–6 (8). Female catkins are erect during anthesis, but otherwise pendant. They develop into small, woody, superficiallycone-like oval dryfruit2 to 3 cm (3⁄4 to1+1⁄4 in) long. Theseeds develop between the woody bracts of the 'cones' and are shed in late autumn and winter. Red alder seeds have a membranous winged margin that allows long-distance dispersal.[7]
Specimens can live to about 60 years of age before being seriously afflicted byheart rot.[8]
The name derives from the bright rusty red color that develops in bruised or scraped bark.[7]
Alnus rubra grows fromSoutheast Alaska to central coastalCalifornia, nearly always within about 200 kilometres (120 mi) of thePacific coast, except for an extension 600 km (370 mi) inland acrossWashington andOregon into northernmostMontana.[5][9] It can be found from sea level to elevations of 900 m (3,000 ft).[8]
In southern Alaska, westernBritish Columbia and the northwesternPacific Coast Ranges of the United States, red alder grows on cool and moist slopes; inland and at the southern end of its range (California) it grows mostly along the margins of watercourses and wetlands.[10] It isshade intolerant.[8]
In moist forest areas,Alnus rubra willrapidly cover a former burn orclearcut, often preventing the establishment ofconifers. It is a prolific seed producer,[8] but the small, wind-dispersed seeds require an open area of mineralsoil togerminate, and so skid trails and other areas disturbed by logging or fire are ideal seedbeds. Such areas may host several hundred thousand to several million seedlings per hectare in the first year after landscape disturbance.[11]
Twigs and buds of alder are only fair browse for wildlife, butdeer andelk browse the twigs in fall and twigs and buds in the winter and spring.Beaver occasionally eat the bark, though it is not a preferred species. Severalfinches eat alder seeds, notablycommon redpoll andpine siskin, and as dodeer mice.Tent caterpillars often feed on the leaves, but the trees usually recover within a year.[8]
The tree hosts thenitrogen-fixing actinomyceteFrankia in nodules on roots. This association allows alder to grow in nitrogen-poor soils, and makes the species an important early colonizer of disturbed forests and riparian areas. This self-fertilizing trait allows red alder to grow rapidly, and makes it effective in covering disturbed and/or degraded land, such asmine spoils. Imported Red Alder has been found to be able to make successful associations with Frankia strains present in the UK.[12] Alder leaves, shed in the fall, decay readily to form a nitrogen-enrichedhumus making the nitrogen available to other species.
Red alder is associated withcoast Douglas-fir (Pseudotsuga menziesii subsp.menziesii),western hemlock (Tsuga heterophylla),grand fir (Abies grandis),western redcedar (Thuja plicata), andSitka spruce (Picea sitchensis) forests.
Along stream banks, it is commonly associated withwillows (Salix spp.),red osier dogwood (Cornus stolonifera),Oregon ash (Fraxinus latifolia), andbigleaf maple (Acer macrophyllum).
To the southeast of its range it is replaced bywhite alder (Alnus rhombifolia), which is a tree of similar stature, but which differs in the leaf margins not being rolled under, lack of distinct lobes, and lack of membranous wings on seed margins. In the high mountains it is replaced by the smaller and more shrub-likeSitka alder (Alnus viridis subsp.sinuata), and east of theCascade Mountains bythinleaf alder (Alnus incana subsp.tenuifolia).
A russet dye can be made from a decoction of the bark, apparently due to thetannin it contains,[8] and was used byNative Americans to dye fishing nets so as to make them less visible underwater.[8]
Native Americans used red alder bark to treatpoison oak reactions, insect bites, and skin irritations. Blackfeet Indians used an infusion made from the bark of red alder to treat lymphatic disorders and tuberculosis. Recent clinical studies have verified that red alder containsbetulin andlupeol, compounds shown to be effective against a variety oftumors.[13]
In addition to its use as a nitrogen fixer, red alder is occasionally used as arotation crop to discourage the conifer root pathogenPhellinus weirii (causinglaminated root rot).
Alnus rubra are occasionally planted asornamental trees and will do well inSwales,riparian areas, or on stream banks, in light-textured soils that drain well. Red alder does not thrive in heavy, wet clay soils. If planted domestically, alders should be planted well away from drainpipes,sewage pipes, and water lines, as the roots may invade and clog the lines.[citation needed]
Alder lumber is not considered to be a durable option for outdoor applications,[who?] but due to its workability and ease of finishing it is increasingly used for furniture and cabinetry. Because it is softer than other popular hardwoods such asmaple,walnut andash, alder has historically been considered of low value fortimber. However it is now becoming one of the more popular hardwood alternatives as it is economically priced compared to other hardwoods. In the world of musical instrument construction, red alder is valued by some electric guitar / electric bass builders for its balanced tonality. Alder is frequently used by Native Americans for making masks, bowls, tool handles, and other small goods.
The appearance of alder lumber ranges from white through pinkish to light brown, has a relatively soft texture, minimal grain, and has medium luster. It is easily worked, glues well, and takes a good finish.
Because of its oily smoke,A. rubra is a is the wood of choice for smoking salmon.[14]
Red alder is often used by scientists as abiomonitoring organism to locate areas prone toozone pollution, as the leaves react to the presence of high ozone levels by developing red to brown or purple discolorations.[15]
With a current inventory of about 7.4 billion cubic feet (210 million cubic metres), red alder comprises 60% of the total hardwood volume in the Pacific Northwest, and is by far the most valuable hardwood in term of diversity of products, commercial value, and manufacturing employment.[16] Increasing value of alder logs, combined with a better understanding of the species' ecological role, has led some land managers to tolerate and, in some cases, manage for alder.
As an "aggressive pioneer" that was freely able to rapidly colonise areas to the detriment of the more valuable conifer species, it was regarded for a long time as a weed[17] and was neglected for its timber potential, however breeding programmes to improve stem form and timber quality[18] are now underway.
Since most forest land in the Northwest is managed for conifer production, over 200,000 acres (80,000 hectares) of timberland are sprayed withherbicides annually in Oregon alone to control red alder and other competing hardwood species.[19] Red alder's rapid early growth can interfere with establishment of conifer plantations.[20] Herbicide spraying of red alder over large areas of coastal Oregon and Washington has resulted in a number of lawsuits claiming it has caused health problems, includingbirth defects and other human health effects.[21][22]
In addition to adding soil nitrogen, rotations of red alder are used to reduce laminated root rot in Douglas-fir forests. Nurse stands of red alder may also reduce spruce weevil damage in Sitka spruce stands on the Olympic Peninsula.[23] Alder continues to attract interest as log values approach and often exceed those of Douglas-fir.[24] This interest is limited by red alder's total stand productivity, which is significantly lower than that of Douglas-fir and western hemlock.
