Prota 7(2): Timbers/Bois d’œuvre 2
Humb., Bonpl. & Kunth, Nov. gen. sp. 2: 20 (1817).
2n = 28
Andean alder, Andes alder, alder (En). Aulne des Andes, aune des Andes, aulne d’Amérique (Fr).
Origin and geographic distribution
Andean alder is found in the wild in high altitude areas from Mexico to Argentina. In Argentina it is one of the major timber species. In tropical Africa it has been introduced in Rwanda, Burundi, Kenya, Uganda and Madagascar. It is also planted in Japan, Australia and New Zealand.
Andean alder was introduced in tropical Africa, especially in Madagascar, for the production of timber. The wood is used in construction, carpentry, furniture, carving and turnery, and is suitable for the production of pencils, matches, matchboxes, plywood and particle board. Both in its native range as well as in tropical Africa it is increasingly planted for reclamation of denuded sites, erosion control, soil improvement and in agroforestry systems. It is well suited for these purposes because of its rapid growth and tolerance to a wide range of soils and climatic conditions. Where planted in agropastoral and agroforestry systems, it has improved growth and protein content of pasture grasses. Soil organic matter and nitrogen content increased under trees and beside hedges. A 33% increase in weight gain of cattle grazing under Andean alder has been reported compared to open pastures. The tree is planted to provide shade in grazing areas and gardens.
Its fast growth and burning properties make Andean alder well suited for the production of firewood and charcoal. The leaves provide a good browse for livestock.
In its native range, macerated leaves are used to treat joint and muscular pains, rheumatism and skin infections. A leaf infusion is part of a cure for inflammation of the prostate.
With appropriate techniques a good quality paper can be produced from Andean alder wood.
Andean alder wood is medium-weight with a specific gravity of 0.35–0.60. It can be dried moderately rapidly, without much cracking or twisting, and has good dimensional stability. The wood is easy to work. It is rated as moderately durable, but is durable under water. It is moderately difficult to impregnate with preservatives. The pulp has excellent qualities for paper making.
The leaves are palatable for livestock and contain about 16% of crude protein. The bark is rich in tannin.
Deciduous medium-sized tree up to 30(–40) m tall; bole cylindrical, up to 50(–100) cm in diameter; bark surface smooth and grey in young trees, but becoming scaly and ridged with age; crown narrow, dense; young twigs glandular hairy, branchlets with lenticels and conspicuous rounded scars from fallen leaves. Leaves alternate, in 3 rows, simple and entire; stipules ovate to elliptical, 4–8 mm × 1–1.5 mm; petiole (4–)7–23(–35) mm long; blade lanceolate, ovate or elliptical, thinly leathery, (3.5–)5.5–14(–19) cm × (2–)3–9(–10.5) cm, cuneate to obtuse or rounded at base, long-acuminate to rounded at apex, margin toothed, glandular hairy, pinnately veined with 10–15 pairs of lateral veins. Inflorescence a many-flowered catkin; male catkin elongate, pendulous, 5–11 cm long, flowers arranged in groups of 3 in bract axils; female catkin ovate or elliptical, 3–6 mm × 1.5–3 mm, flowers arranged in groups of 2 in bract axils. Flowers unisexual, minute; male flowers 4-merous, with elliptical or obovate perianth segments c. 1.5 mm long, stamens opposite and basally adnate to perianth segments, 2.5–4 mm long; female flowers consisting of a 2-celled ovary with a 2-branched style. Fruit an elliptical to obovate, winged nut 1.5–3 mm long, dark brown, in cone-like, ovoid to ellipsoid infructescence 1–3 cm × 1–1.5 cm. Seedling with epigeal germination; cotyledons leafy, spreading; first 2 leaves opposite.
Andean alder fixes nitrogen in symbiosis with Actinomyces alni (synonym: Frankia alni). The flowers are wind pollinated.
Alnus comprises about 40 species, most of them in temperate and subtropical regions of the Northern Hemisphere.
Alnus nepalensis D.Don, native of mainland Asia and Japan, has also been introduced in Africa. It has roughly the same uses as Andean alder and is also being promoted for use in agroforestry systems, but it is better adapted to semi-arid environments.
Alnus acuminata and Alnus jorullensis Kunth have often been confused. The latter is restricted to Mexico and Guatemala and differs in leaf shape and in its scrubby habit; it is found in drier habitats.
Andean alder occurs naturally in the range of 18°N–28°S at altitudes of 1500–3200(–3700) m. It can withstand temperatures below zero for a short time and is adapted to high humidity. Protection from cold dry winds is beneficial. It regenerates well on degraded land and steep mountain slopes.
Andean alder can be propagated with seed and cuttings, or by tissue culture. The 1000-seed weight is 0.2–1.5 g. The germination of fresh seed is 50–70%, but seed looses viability after 3–6 months. When sown in containers in nurseries, transplanting in the field is done after 6–8 months. Direct sowing and planting bare-root seedlings or stumped cuttings are also practised. Improved selections are multiplied by tissue culture. Inoculation with the correct strain of Actinomyces alni is profitable. Planting closely, at 2 m × 2 m, is recommended to produce straight boles. Young trees need protection from grazing animals for 1–3 years after planting. Thinning is recommended after the third year and after 10–15 years to arrive at a final density of 250–350 trees/ha. The recommended rotation is 20 years and it would yield annually up to 15 m³/ha.
Planting as a windbreak is done at 1–1.5 m spacing. Regular pruning of branches should control width and shading. In East Africa, especially in nurseries, serious diseases are damping-off, Septoria brown leaf spot and stem canker. In Uganda honey bees collect the resin from the glands on buds and young leaves to make so-called propolis to protect their nests. On doing so, they may cause serious damage and leaf fall.
Genetic resources and breeding
Provenance trials in New Zealand have shown a high variation in performance and environmental tolerance between accessions. Selection for form, growth rate, resistance to drought and disease have resulted in lines suitable for different growing conditions and uses. Selection for specific uses and conditions in tropical Africa will be rewarding as variation within the species is huge.
Some Alnus species spread enough to be considered nuisance weeds. There is no reported evidence at present that this occurs with Andean alder but it has not been widely planted as yet, so the opportunity for it to spread may not have arisen. Given its palatability for livestock, this may never become an issue.
Large-scale planting for timber production will require research into appropriate management and identification of suitable selections.
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Correct citation of this article:
Bosch, C.H., 2009. Alnus acuminata Kunth. In: Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). Prota 7(2): Timbers/Bois d’œuvre 2. [CD-Rom]. PROTA, Wageningen, Netherlands.