Alnus acuminata: valuable timber tree for tropical highlands
Alnus acuminata is a fast-growing species valued for its wood,
watershed protection and soil improvement. Native from Mexico to Northern
Argentina, it is known as alive (Mexico, Argentina, Colombia, Ecuador and Peru);
aile, ilite (Mexico); ramrám, lambrán (Guatemala, Costa Rica and Peru); jaúl
(Costa Rica); palo de lama (Guatemala) and; cerezo and chequiro (Colombia).
Easily propagated from seed or by natural regeneration, A. acuminata is a
popular agroforestry species in its native range. It has been successfully
introduced into southern Chile and southern New Zealand.
Botany
Alnus acuminata ssp. arguta (Schlectendal) Furlow (Betulaceae)
grows to 30 m in height and to 50 cm in diameter (after 30 years) in natural
conditions. Maximum age may be 60 years (L Fournier,, personal communication).
The leaves are simple, alternate, elliptical, 6 to 15 cm long, 3 to 8 cm wide,
border double dentate, deciduous or semideciduos. The upper leaf surface is dark
green and the lower surface is pale, whitish to light green. The bark is
light-gray or silvery with yellowish lenticels. Crown shape is open rounded to
pyramidal. Male and female flowers occur in separate catkins on the same branch.
Inflorescences are cone-like with lignified scales, dark brown when ripened, and
bearing more than 100 fruits per cone. The fruit is a small membranous-winged
samara, 2 to 3 mm long that contains one seed. Dispersal is mainly by the wind.
Seeds ripen in February,, March and August in South America (NAS, 1980), and
from September to January in Costa Rica (Rotas et al., 1991).
There is considerable confusion in the taxonomy of Alnus
acuminata. Furlow (1977) reported the species as Alnus acuminata H B.K, but in
his last revision (1979) he classified it as Alnus acuminata ssp. arguta. The
species also has been described as Alnus jorullensis H.B.K. by Carlson and
Dawson (1985). Holdridge (1951) concluded that if subspecies populations exist
they apparently intergrade into each other and because of similarities in wood
and silvicultural characteristics they may be considered as a single species, at
least from a forestry viewpoint.
Distribution and ecology
Alnus acuminata is native to the American contient ranging from
Mexico to Northern Argentina in elevations between 1,200 and 3,200 m.a.s.i.
where annual rainfall is 1,000 to 3,000 mm or more. The species occurs where
mean annual temperature ranges between 4° and 27°C; however it can
withstand temperatures dipping briefly below 0°C (NAS, 1980).
Alnus acuminata is a fast-growing pioneer species that
regenerates naturally in open, disturbed areas. It grows in moist soil
environments' usually along the banks of streams, rivers, ponds, and swamps
where it typically forms dense pure stands.
It also can be associated with wet flood plains, or moist
mountain slopes, although it may be adapted to somewhat drier conditions.
However, it is usual' restricted to zones with extra soil moisture such as cool,
tropical highlands, and cool, high-ladtude regions with abundant rainfall where
mist and cloud cover can be a source of fog-drip precipitation. In tropical
highlands of Central and South America, clouds and mist are important in
supporting Alnus acuminata and grass, when associated, through the dry season.
Alnus acuminata prefers deep, well-drained soils with high
organic matter content. However, it is commonly found growing on shallow soils,
such as landslides. Rojas et al. (1991) report that it will grow in soil with pH
as low as 45.
Uses
Timber.
Alnus acuminata wood is light brown-yellow to pink, odorless'
and tasteless' without differences between the heartwood and the sapwood.
Reports on specific gravity vary from 034 to 039 (Tuk, 1980) and 05 to 0.6 (NAS,
1980). The calorific value is 19,2501kJ/kg (CATIE, 1986). The wood dries easily
and preserves well. It has even grain, seasons fairly well, and is easy to work
and finish by hand or machine. Despite its light weight it is tough and strong,
and is sometimes used for construction. Timber is also used for fuelwood, posts'
poles, light lumber, boxes, broom handles, domestic implements, plywood cores,
particle board, and musical instruments. A match company in Colombia evaluated
more than 20 native species and found Alnus acuminata wood best suited for
making stick matches (In". R. Arismendi, Personal Communication).
Agroforestry.
Farmers in Costa Rica have grown Alnus acuminata in pastures and
as a shade tree for coffee crops for more than 90 years. Trees are regenerated
naturally or planted from nursery stock at spacings of 8 to 14 m (about 100
trees/ha).
One benefit of including trees in cattle pastures is greater
milk production-cows on pastures with Alnus acuminata produce more than cows on
pastures without it (Budowski, 1983). Farmers in Costa Rica sometimes construct
crude fences around individual seedlings to protect them from
livestock-protection is needed until trees grow tall enough that livestock can
not browse new growth.
Silviculture
Propagation.
Alnus acuminata is propagated by seeds (more than 2 million pure
seeds/kg). Seeds are recalcitrant and must be planted quickly-viability
decreases from 70% to 20% in a few months. Seed viability can be extended by
storing seed in airtight containers at 5° Cviability is 50% and 31 % after
2 and 3 months, respectively (Rojas et al., 1991).
No seed pre-treatment is necessary. Rojas et al. (1991)
recommend broadcasting seed in germination beds (15 to 20 g of seed per m²
of bed) and covering them with a very thin layer of mixed soil and sand. The
germination bed should be a 1:1:2 mixture of fine soil, sand and organic
material. Seeds should be watered twice daily with a very fine mist to maintain
soil humidity. Overwatering may cause damping-off. Germination starts 6 to 7
days after sowing and is complete within 15 days. The most vigorous seedlings
should be transplanted to pots or back plastic bags 20 days after germination.
Seedlings may be planted out when they are 20 cm tall (in about four months).
Bare-root seedlings and stump cuttings are possible alternatives to
container-grawn seedlings. Seedlings do not compete well with weeds so frequent
weeding is important (Rojas et al., 1991).
Management.
Alnus acuminata is grown in plantations mainly in Colombia and
Costa Rica, but in other countries as well. In Colombia, an initial spacing of
2.6 x 2.6 m (1,480 trees/ha) is common (Sicco Smit, 1971). In Costa Rica, an
initial spacing of 3 x 3 m is preferred. At least two thinnings are recommended,
the first after the third year and the second after 10 to 15 years, leaving 250
to 350 trees per hectare. Trees are harvested in rotations of about 20 years.
Average annual wood production is 15 to 20 m³ per hectare. According to
Canet (1985), a stand of 30-year-old trees with a density of 35 trees/ha yielded
70 m³/ha of timber, 183 ton/ha of dry fuelwood, and 3.6 ton/ha of leaves
and fine branches. Alnus acuminata resprouts vigorously from the stump after
cutting.
Symbiosis
Alnus acuminata, like other Alnus species, forms a symbiosis
with actinomycetes of the genus Frankia. Rojas et al. (1991) report that nodules
begin to grow on 13-day-old nursery seedlings. Estimates of nitrogen fixation
for Alnus species vary widely between 62 kg/ha/yr for A. sinuata in Alaska and
125 kg/ha/yr for A. glutinosa, to 320 kg/halyr for A. rubra in Oregon (Carlson
and Dawson, 1985). In a 2year-old A. acuminata plantation in the Colombian
highlands (1200 trees/ha), Carlson and Dawson (1985) estimate an annual increase
in soil nitrogen of 279 kg/ha. Acetylene reduction values for 120-day-old A.
acuminata greenhouse seedlings inoculated with a crushed nodule suspension were
between 32.5 and 86.4 µmol of ethylens produced per gram of nodule dry
weight per hour (Russo and Berlyn, 1988).
Pests and diseases
Alnus acuminata is susceptible to attack by defoliators
(Nodonota irazuensis and Nodonota cat parvula, Coleoptera, Chrysomelidae). A
stem borer Scolytodes alni, (Coleoptera, Scolytidae) has been observed in Costa
Rica during the dry season. Vertebrates such as Sciurus sp. (Rodentia,
Sciuridae) may cause debarking and Sylvilagus brasiliensis (Lafomorpha,
Leporidae) may destroy seedlings. Fungi such as Fusarium sp. and Trichoderma sp.
may damage seeds; Colletotrichum sp. and Phomopsis sp. may affect leaves; and
Rosellinia sp. may affect stems and roots in mature trees (CATIE, 1991).
References
Budowski, G. 1983. An attempt to quantify some current
agroforestry practices in Costa Rica. In Huxley, P. A. ed. Plant Research in
Agroforestry. Nairobi, Kenya, ICRAF. pp. 43-62.
Canet, G.C. 1985. Caracteristicas del sistema silvo-pastoril
jaúl (Alnus acuminata) con lecheria de altura en Costa Rica. In R. Salazar ed.
Técnicas de producción de leña en fincas pequenas. Actas de los simposios.
CATIE, Turrialba, 2428 de junio, 1985. pp. 241-249.
Carlson, P.J. and J.O. Dawson. 1985. Soil nitrogen changes,
early growth, and response to soil internal drainage of a plantation of Alnus
jorullensis in the Colombian highlands. Turrialba 35(2):141-150.
CATIE 1986. Silvicultura d e especies promisorias para
producción de leña en America Central. CATIE, Turrialba, Costa Rica. p. 51.
CATIE 1991. Plagas y enfermedades forestales en America Central:
guía de campo. CATIE, Turrialba, Costa Rica.185 p.
Furlow, J.J. 1977. Betulaceae. In Burger, W. Flora
Costaricensis. Fieldiana: Botany 40:56-58.
Furlow, J.J. 1979. The systematics of the American species of
Alnus (Betulaceae). Rhodora 81(825):1-121.
Holdridge, L.R. 1951. The alder, Alnus acuminata, as a farm
timber tree in Costa Rica. Caribbean Forester 12(2):47-57.
National Academy of Sciences. 1980. Firewood crops: shrub and
tree species for energy production. Vol. 1. National Academy of Sciences,
Washington, D.C.
Rojas, F., G. Torres, E. Arnáez and I, Moreira. 1991. Jaúl
cuadernos cientificos y tecnológicos, especies forestales tropicales, No. 1.
Instituto Tecnológico de Costa Rica, Cartago, Costa Rica. 9 p.
Russo, R.O. and G.P. Berlyn. 1989. The effect of a new growth
biostimulant on acetylene reduction in nodulated seedlings of Alnus acuminata.
Nitrogen Fixing Conference Abstracts. Ames, Iowa. July 30-August 3, 1989.
Sicco Smit, G. 1971. Notas silviculturales sobre Alnus
jorullensis de Caldas, Colombia. Turrialba 21:83-88.
Tuk, J. 1980. Informe general del proyecto: Clasificación y
normalización de maderas para uso estructural. Instituto Tecnológico de Costa
Rica, Cartago, C.R.
A publication of the Nitrogen Fixing Tree Association Winrock
International 38 Winrock Drive Morrilton AR 72110-9537
NFTA 95-02 (Replaces 87-06) January
1995
