Acacia auiculiformis - a multipurpose tropical wattle
Acacia auriculiformis A. Cunn. ex Benth. is a multipurpose,
leguminous tree in the subfamily Mimosoideae. It has been planted for fuelwood
production, erosion control, ornament and shade in many tropical areas in the
world. Its rapid early growth: ability to fix nitrogen; tolerance of infertile,
acid. alkaline, saline or seasonally waterlogged soils; and tolerance of
moderate dry seasons make it a very useful species for rehabilitation of
degraded lands. The scientific name comes from the Latin 'auricula'-external ear
of animals and 'forma' form, figure or shape', in allusion to the shape of the
pod.
Acacia auriculiformis
Botany
It is commonly a tree, 8-20 m in height, heavily branched with a
short bole. On favorable sites it can grow to 30 40 m tall and 80100 cm diameter
with a straight, single stem. The bark is gray or brown, more or less smooth in
young trees. becoming rough and longitudinal fissured with age. Mature foliage
consists of phyllodes, which may be straight or falcate, acute or sub-falcate,
10-20 cm long and 1.5-3.0 cm wide. Phyllodes of sapling may attain 30 cm in
length and up to 5.0 cm in width. There are 3 prominent longitudinal nerves
running together towards the lower margin or in the middle near the base, with
many fine crowded secondary nerves, and a distinct gland at the base of the
phyllode (Pedley 1978).
Inflorescences are in spikes up to 8 cm long in pairs (seldom
three) in the upper axils. Each inflorescence is comprised of about 100 tiny
(3.8x4.1 mm) bright yellow flowers (Ibrahim and Awang 1991). Flowers are
5-merous; the calyx 0.7-1.0 mm long, with short lobes; the corolla is 2-2.5
times as long as the calyx. Stamens are approximately 3 mm long. The pods are
slightly woody, glaucous and transversely veined, about 6.5 cm long and 1.5 cm
wide. They are initially straight or curved but become very twisted and
irregularly coil on maturity. The seeds are broadly ovate to elliptical, about
4-6 mm long and 3 4 mm wide. Each seed is encircled by a long red, yellow or
orange funicle. There are 60,000 seeds per kg.
Ecology
Acacia auriculiformis occurs from near sea level to 400 m, but
is most common at elevation less than 80 m. It is predominntly found in the
seasonally dry tropical lowlands in the humid and subhumid zones. The mean
annual rainfall in its natural range varies from 700-2000 mm, and the dry season
(i.e. monthly rainfall less than 40 mm) may be 7 months. The mean maximum
temperature of the hottest month is 32-34°C and the mean minimum of the
coolest month is 17-22°C.
The species is commonly riparian, i.e. ringing perennial rivers
and semi-perennial creeks, and tends to form discontinuous populations along
drainage systems. It is found most commonly on clay soil types, found most
commonly on clay soil types however it exhibits the ability to grow in a variety
of soils including calcareous sands and black cracking clays. It can also
tolerate highly alkaline and saline soils. Seedlings have the ability to compete
with Imperata cylindrica during early growth phases and once mature may reduce
the grass to a sparse ground cover.
Distribution
Acacia auriculiformis is endemic to Australia, Papua New Guinea
and Indonesia. having a disjunct distribution in three main areas: the lowlands
of southern half of the island of New Guinea (Papua New Guinea and Irian Jaya,
Indonesia); the lowlands of tropical Northern Territory, Australia; and the Cape
York Peninsula of northern Queensland, Australia It has been widely introduced
to many tropical countries in South and Southeast Asia Africa and Latin America.
Uses
Wood.
Heartwood varies from light brown to dark red. The wood makes
attractive furniture and is suitable for construction work, turnery and carving.
Plantation-grown trees have shown promise for the production of unbleached kraft
pulp-for bags and wrapping paper; and high quality neutral sulphite semichemical
pulp-for corrugating, medium and higher-grade packaging products (Logan 1987).
The wood has a high basic density (500650 kg/m³) and a calorific value of
4700-4900 kcal/kg, which make it ideal for firewood and charcoal.
Land Rehabilitation & Landscaping.
The spreading, denselymatted root system stabilizes eroding
land. Its rapid early growth even on infertile sites, and tolerance of both
highly acidic and alkaline soils make it popular for stabilizing and
revegetating mine spoils. It is used for shade and ornamental purposes in cities
where its hardiness, dense foliage and bright yellow flowers are positive
attributes.
Other Uses.
The bark has sufficient tannins for possible commercial
exploitation (Abdul Razak et al. 1981). A natural dye, used in the batik textile
industry in Indonesia, is also extracted from the bark. Its flowers are a source
of bee forage for honey production (Moncur et al. 1991).
Silviculture
Propagation.
Propagation is generally by seed. Pregermination treatment is
essential to promote seed germination. Immersion of seed in ample boiling water
for 1-2 minutes is suitable to break dormancy. Germination is rapid after
pretreatment and typically exceeds 70%. In general, 3-4 months are needed to
raise seedlings to a plantable size, 25 cm in height. Inoculation with
appropriate rhizobia may be beneficial, especially when seedlings are raised in
sterilized soil.
Management.
Establishment is successful by containerized seedlings or by
direct seeding. Containerized seedlings generally give higher survival,
especially in areas of heavy weed competition. In the field, weed control is
essential during the first 1-2 years. A small dose of NPK fertilizer in the
first year helps improve initial growth - fertilization rates depend on quality.
Recommended spacing is 2x2 or 2x4 m. Acacia auriculiformis has the ability to
coppice, but it is not a vigorous sprouter. It responds well to pollarding.
Yield.
An increment in height of 2-4 m per year in the first few years
is common even on soils of low fertility (Boland 1989). On relatively fertile
Javanese soils receiving 2000 mm annual rainfall, a mean annual increment of
15-20 m³/ha is obtainable but on less fertile or highly eroded sites the
increment is reduced to 8-12 m³/ha (Wiersum and Ramlan 1982). Recommended
rotation is 4-5 years for fuelwood, 8-10 years for pulp and 12-15 years for
timber. One or two thinnings are required with longer rotations, depending on
initial spacing, site quality and tree growth.
Symbiosis
Acacia auriculiformis can fix nitrogen after nodulating with a
range of Rhizobium and Bradyrhizabium strains. It also has associations with
both ecto- and endo-mycotthizal fungi.
Limitations
The propensity to produce multiple and crooked stems reduce its
utility. It is susceptible to fire; even trees 10-15 years old can be killed.
Stressed trees are found to be highly susceptible to attack by leaf insects.
Genetics & Provenances
Isozyme studies revealed marked genetic variation in A.
auriculiformis. Three distinct groups of populations corresponding to the
geographic distribution in Papua New Guinea, Queensland and Northern Territory
(Wickneswari and Norwati 1991). These regional groupings are also apparent in
seedlling morphology (Pinyopusarerk et al. 1991). Additionally, field trials
have shown marked differences in growth and form. Provenances from Papua New
Guinea have the highest production while those from Queensland have a high
proportion of single stems. Those from the Northern Territory are inferior in
both growth and form (Harwood et al. 1991).
Research Needs
Selection and breeding for superior growth and stem form are now
underway in many countries, including Thailand and Vietnam Natural hybrids of A.
auriculiformis x A. mangium have shown desirable characteristics; e.g. vigor,
fine branching and tendency for a strong apical dominance. These characteristics
lead to healthy trees with single stems and a good clear bole. Production and
vegetative propagation of these hybrids warrant detailed study.
References
Abdul Razak, MA, Low, C.K and Abu Said, A. 1981 Determination of
relative tannin contents of the barks of some Malaysian plants. Malaysian
Forester 44:87-92.
Boland, D.J. (ed.). 1989. Trees for the tropics: growing
Australia, multipurpose trees and shrubs in developing countries. ACIAR
Monograph No. 10,247 pp.
Harwood C.E., Matheson, A.C. Gororo, N. and Haines, M.W. 1991
Seed orchards of Acacia auriculiformis in Melville Island, Northern Territory,
Australia. In: J.W. Turnbull (ed), Advances in topical acacia research. ACIAR
Proceedings No. 35. pp 8791.
Ibrahim, Z. and Awang, K 1991. Comparison of floral morphology
flower production and pollen yield of Acacia mangium and A auriculiformis. In:
Advances in tropical acacia research. pp 26-29 See Harwood at al. 1991.
Logan, A.F. 1987. Australian acacias for pulpwood In: J.W
Turnbull (ed), Australian acacias in developing countries. ACIAR Proceedings No.
16. pp 89-94.
Moncur, M W., Kleinschmidt, G. and Somerville, D. 1991. The role
of acacia and eucalypt plantations for honey production. Advances in tropical
acacia research. pp 123-27. See Harwood e al. 1991.
Pedley, L. 1978. A revision of Acacia Mill. in Queensland
Austrobaileya 1(2):75-234.
Pinyopusarerk. K Williams, E.R, Boland, D.J. 1991. Geographic
variation in seedling morphology of Acacia auriculiformis. Australian Journal of
Botany 39:247-260.
Wickneswari, R. and Norwati, M. 1991. Genetic structure of
natural populations of auriculiformis in Australia and Papua New Guinea In:
Advances in tropical acacia research. pp 94-95. Se Harwood e' al. 1991.
Wiersum. K.F. and Ramlan, A. 1982. Cultivation of Acacia,
auriculiformis in Java, Indonesia Commonwealth Forestry Review 61:135-144.
NFTA 95-05 September
1995
