2983

11: Auxiliary plants

Acacia crassicarpa A. Cunn. ex Benth.

London Journ. Bot. 1: 379 (1842).

LEGUMINOSAE - MIMOSOIDEAE

2n = 26

Racosperma crassicarpum (A. Cunn. ex Benth.) Pedley (1987).

Northern wattle, Papua New Guinea red wattle (En).

Acacia crassicarpa occurs naturally in north-eastern Queensland, south-western Papua New Guinea and south-eastern Irian Jaya. Experimental plantings have been made in several countries in South-East Asia.

The wood of Acacia crassicarpa is suitable for firewood, making charcoal and timber, e.g. for construction, furniture, flooring, board, boat building. It appears suitable for pulping, but more study is required to confirm this use. The tree provides shade and can be planted for weed control and is often cited as an effective species for the rehabilitation of land infested with Imperata cylindrica (L.) Raeuschel. In Papua New Guinea, it is reported to be a very vigorous colonizer of degraded soils following shifting cultivation.

The leaves decompose slowly and are useful as mulch. The sapwood is pale yellowish-brown and heartwood golden-brown. The wood is strong and durable with a density of 670—710 kg/m³ at 12% moisture content and a basic density of 620 kg/m³. Its energy value is 22 600 kJ/kg. The weight of 1000 seeds is 20—30 g.

A small to medium-sized tree, up to 25(—30) m tall; bole often straight and branchless for up to 13—18 m, up to 50 cm in diameter, sometimes fluted at base. Bark dark or grey-brown, hard, with deep vertical furrows; inner bark red and fibrous. Phyllodes falcate, 8—27 cm x 1—4.5 cm, 2.5—12 times as long as wide, greyish-green, glabrous; primary veins 3—5, prominent, yellowish, longitudinal, tending to run into the lower margin at the base; secondary veins parallel, not anastomosing, crowded; pulvinus 4—20 mm long with a circular gland at top. Inflorescence a bright yellow spike, 4—7 cm long, clustered in groups of 2—6 in the upper axils; peduncle 5—10 mm long, rachis thick; flowers 5-merous, bisexual; calyx broadly cupular, 0.5—0.7 mm long, lobes concave, lobed to about halfway down; corolla widely spreading, glabrous, 1.3—1.6 mm long, 2—3 times as long as the calyx; stamens 2—3 mm long; ovary shortly pubescent, more densely hairy at the top. Pod woody, ovoid-oblong, flat, 5—8 cm x 2—4 cm, glabrous, dull brown, transversely veined but hardly reticulate. Seed oblongoid, 5—6 mm x 2—3 mm, black, arranged transversely in separate compartments; areole large and almost closed; funicle folded and thickened, forming a long aril below the seed, pale creamy-yellow.

Young seedlings first produce pinnate leaves, but develop phyllodes from the 3rd or 4th leaf pair. Under favourable conditions, seedlings grow rapidly reaching 25—30 cm in 3—4 months. Acacia crassicarpa is one of the fastest growing tropical Acacia spp. It appears to maintain active shoot growth almost the year round, although a few months of stagnation may occur in the dry season.
In Sabah, it attained a mean height of 15—23 m and a mean diameter of 10—16 cm in 4 years, outperforming other fast-growing Acacia species including Acacia auriculiformis A. Cunn. ex Benth. and Acacia mangium Willd. Assessment at 15 months after planting in a progeny/provenance trial in northern Australia showed that the mean height and diameter at breast height of Papua New Guinea provenances were 5.2 m and 5.1 cm respectively. The corresponding averages for Queensland provenances were 3.3 m and 2.9 cm respectively. This faster growth of Papua New Guinea provenances is consistent with results from trials in southern China, southern Queensland and Thailand. In Queensland, Acacia crassicarpa trees are often small, hardly exceeding 10 m; the typical form is bushy with a heavy crown, although long and straight boles can also be found.
Flowering starts as early as 18 months after planting, while seed is produced in abundance after 4 years. Seeds mature 5—6 months after flowering. In its natural range it flowers from June to September and bears mature fruits from October to March.
Acacia crassicarpa is a vigorous atmospheric nitrogen fixer and nodulates well with a group of related Rhizobium strains.

Acacia crassicarpa is sympatric with Acacia aulacocarpa A. Cunn. ex Benth. to which it is closely related. Acacia crassicarpa is distinguished by its broader and more woody pods. Acacia crassicarpa may infrequently form natural hybrids with Acacia aulacocarpa in northern Queensland (Australia).

Acacia crassicarpa occurs mainly in the humid and sub-humid tropics from 8—20°S and from 0—200(—450) m altitude. Annual rainfall in its natural habitat is from as low as 500 mm in Australia to as high as 3500 mm in Papua New Guinea and Irian Jaya. Length of the dry season ranges from 6 months at the southern limit of the distribution area near Townsville, Queensland, to 3 months at the northern limit in Papua New Guinea and Irian Jaya.
The mean minimum temperature of the coolest month is 15—22°C and the mean maximum temperature of the hottest month is 31—34°C. No frost occurs in its natural range.
In Australia, Acacia crassicarpa is commonly found immediately behind beaches, on the coastal plains and foothills. It appears to be tolerant of salt spray and soil salinity. It occurs on a variety of soil types, from calcareous beach sands, yellow earths derived from granite, red earths on basic volcanic rock to alluvial and colluvial soils derived from a variety of parent material. In Papua New Guinea and Irian Jaya Acacia crassicarpa is found on the gently undulating terrain of the Oriomo Plateau, on well-drained, strongly acid soils, and also on imperfectly drained soils that flood in the wet season. On former rain forest wetlands with a sandy-loam soil it is superior in growth to Acacia mangium Willd. In the southern coastal lowlands of Queensland Acacia crassicarpa occurs in the understorey of open forest and in open woodland dominated by Eucalyptus pellita F. v. Mueller, Eucalyptus tereticornis Smith or Eucalyptus tessellaris F. v. Mueller. On frontal sand dunes it is found as a wind-sheared shrub or small tree, 2—8 m tall, behind Casuarina equisetifolia L. and associated with Alphitonia excelsa Reisseck ex Benth. On Cape York Peninsula it is associated with Eucalyptus tetrodonta F. v. Mueller, Allocasuarina littoralis L.A.S. Johnson, and Melaleuca spp. In Papua New Guinea, Acacia crassicarpa occurs frequently with Acacia aulacocarpa, Acacia auriculiformis and Acacia mangium.

Seeds remain viable for many years and heat treatment or nicking of the seedcoat is required to break dormancy. Immersion in boiling water for 1 minute is a suitable treatment. Treated seeds are sown in germination beds. Germinated seedlings having 2 pairs of leaves can be transplanted into polythene bags containing a mixture of soil and river sand. Seedlings are raised under partial shade, then in the open, and planted out when stem height reaches 25—30 cm. Inoculation of nursery seedlings with a selected Rhizobium strain prior to planting out is recommended for maximum nodule development. Vegetative propagation through air layering has given promising results in Thailand.
Spacing of 3 m x 3 m (1100 trees/ha) to 4 m x 4 m (625 trees/ha) is suitable for land reclamation, fuelwood and pulpwood plantations.

On sites dominated by Imperata cylindrica or other weedy plants, weed control is necessary in the first 1—2 years to ensure establishment. Trees do not coppice well. In open situations, the crown is strongly branched and casts a moderate shade. Preliminary observations indicate that Acacia crassicarpa is resistant to low-intensity fires.

Fungal pathogens of leaves and shoots such as Cercospora sp. can affect productivity, particularly during prolonged periods of high humidity. Acacia crassicarpa is susceptible to attack by a stemboring beetle (Platypus sp.), in Sabah. The beetle, native to Sabah, bores into the stem and is a vector for fungi and bacteria which weaken and stain the stemwood. Young trees are also attacked by a beetle (Sinoxylon sp.) that girdles small stems and branches of less than 2 cm in diameter, causing them to break at the point of attack.

At Sai Thong in Thailand with 1500 mm mean annual rainfall, Acacia crassicarpa derived from Woroi Wipim in Papua New Guinea produced a total above-ground dry biomass of 207 t/ha in 3 years, much more than several other species tested. At a poorer site in Ratchaburi in central Thailand it performed as well as other Acacia species tested, producing a total above-ground dry biomass of 40 t/ha in 3 years.

The Australian Tree Seed Centre, Commonwealth Scientific and Industrial Research Organization (CSIRO), Canberra has a good coverage of genetic material from the natural range in Australia and Papua New Guinea. The Papua New Guinea Forest Research Institute in Lae supplies seed of Papua New Guinea provenances. Selected Rhizobium strains are available from the Department of Agriculture, University of Queensland, Brisbane, Australia.

Current research is limited to a small number of progeny and provenance trials, which are being converted to seedling seed orchards.

Because of its fast growth and its ability to produce large volumes of wood even on infertile land, Acacia crassicarpa has great potential for various forestry practices. It is also suitable for planting for land reclamation, but is too competitive to grow in combination with annual crops. Investigation into the factors affecting coppicing ability is warranted.

Clark, N.B., Balodis, V., Fang Guigan & Wang Jinxia, 1991. Pulping properties of tropical acacias. In: Turnbull, J.W. (Editor): Advances in tropical acacia research. Proceedings of an international workshop held in Bangkok, Thailand, 11-15 February 1991. ACIAR Proceedings No 35. Australian Centre for International Agricultural Research (ACIAR), Canberra, Australia. pp. 138-144.
Harwood, C.E., Haines, M.W. & Williams, E.R., 1993. Early growth of Acacia crassicarpa in a seedling seed orchard at Melville Island, Australia. FAO Forest Genetic Information 21: 46-53.
Nielsen, I.C., 1992. Mimosaceae (Leguminosae - Mimosoideae). Acacia. In: de Wilde, W.J.J.O., Nooteboom, H.P. & Kalkman, C. (Editors): Flora Malesiana. Series 1, Vol. 11. Foundation Flora Malesiana, Leiden, the Netherlands. pp. 34-64.
Pedley, L., 1978. A revision of Acacia Mill. in Queensland. Austrobaileya 1(2): 147-148.
Sim Boon Liang & Gan, E., 1988. Comparative growth of 5 tropical acacias on four different sites in Sabah. Commonwealth Forestry Review 67: 149-158.
Skelton, D.J. & Howcroft, N.H.S., 1987. Seed production and silvicultural trials of acacias in Papua New Guinea. In: Turnbull, J.W. (Editor): Australian acacias for developing countries. Proceedings of an international workshop, Gympie, Queensland, Australia, 4-7 August 1986. ACIAR Proceedings No 16. Australian Centre for International Agricultural Research, Canberra, Australia. pp. 188-190.
Thomson, L.A.J., 1994. Acacia aulacocarpa, A. cincinnata, A. crassicarpa and A. wetarensis: an annotated bibliography. CSIRO Division of Forestry, Canberra, Australia. 131 pp.
Turnbull, J.W., 1986. Multipurpose Australian trees and shrubs: lesser known species for fuelwood and agroforestry. ACIAR Monograph No 1. Australian Centre for International Agricultural Research, Canberra, Australia. pp. 128-129.

K. Pinyopusarerk & C.E. Harwood

Pinyopusarerk, K. & Harwood, C.E., 1997. Acacia crassicarpa A. Cunn. ex Benth.. In: Faridah Hanum, I & van der Maesen, L.J.G. (Editors): Plant Resources of South-East Asia No 11: Auxiliary plants. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea