Burckella (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Burckella Pierre

Protologue: Not. bot. Sapot.: 3 (1890).

Family: Sapotaceae

Chromosome number: x= unknown

Trade groups

Burckella: moderately heavy hardwood, e.g. Burckella macropoda (Krause) H.J. Lam, B. obovata (J.G. Forster) Pierre.

Vernacular names

• Burckella
• Indonesia: kaum (Irian Jaya).

Origin and geographic distribution

Burckella consists of about 14 species and is distributed from the Moluccas and New Guinea to Fiji, Samoa and Tonga. About 6 species occur in Malesia. B. obovata has the largest area of distribution, from Halmahera (the Moluccas) to Vanuatu, and is cultivated for its fruits in this area and also in Java.

Uses

The wood is suitable for light construction, furniture, doors, interior fittings, flooring, moulding, joinery and veneer; locally it is also used for poles of houses, and in the Solomon Islands also for canoes and carving.

The fruits of B. obovata are edible, and the tree is often cultivated in home gardens. Fruits and leaves are used in New Guinea for making dyes. The bark exudes a latex sometimes utilized in making chewing gum and in electric cables.

Production and international trade

No statistics are available on production and trade,but Japan imports small amounts of Burckella timber, mainly from Papua New Guinea (about 1% of the total timber import from Papua New Guinea). The timber is ranked in Papua New Guinea in MEP (Minimum Export Price) group 2, and in 1992 fetched a minimum price for saw logs of US$ 60/m³. In the Solomon Islands, it is ranked among the commercially important timbers.

Properties

Burckella is a moderately heavy and hard wood, resembling nyatoh from other Sapotaceae genera such as Palaquium . The heartwood is pinkish-brown to red-brown, and not distinctly demarcated from the paler sapwood which is 4-5 cm wide. The density is 590-790 kg/m³at 15% moisture content. The grain is usually interlocked, sometimes straight, texture moderately fine to coarse.

At 14% moisture content the modulus of rupture of B. macropoda wood from Papua New Guinea is 120 N/mm²and the modulus of elasticity 14 100 N/mm².

Shrinkage during drying is moderate to fairly high: from green to 15% moisture content 1.5-2.1% radial and 4.1-4.9% tangential, from green to 12% moisture content about 2.4% radial and 5.7% tangential, and from green to oven dry 3.9-5.0% radial and 8.3-9.3% tangential. Deformation on cross section (collapse) may be moderately severe during kiln drying. Wet cores may remain after drying and back-sawn planks may develop long surface checks. Preliminary air drying is recommended for thick boards.

The wood contains silica (up to 1.9% in B. obovata ); this may cause problems in sawing. Tests show that the wood performs very good in planing, shaping, boring, mortising and sanding, and fair in turning. The peeling properties are usually poor, even when pre-heated. Dust of dry wood is irritating to nose, throat and eyes.

The wood is only moderately durable. Logs may be attacked by pinhole borers and termites. The sapwood is not susceptible to Lyctus attack. The heartwood is difficult to treat with preservatives, but the sapwood is much easier; a test on wood of B. macropoda using a pressure treatment showed an absorption of the heartwood of 41 kg/m³and of the sapwood of 357 kg/m³.

The yield of pulp is usually low; unbleached pulp is rather dark. However, the yield of pulp of B. macropoda wood for fibreboard may be as high as 85% at a steaming temperature of 185C.

The wood of B. macropoda contains 35% lignin, 67% holocellulose and 50%α-cellulose (calculated on an ash- and lignin-free basis) and 1.9% ash. The solubility is 1.2% in alcohol-benzene, 2.4% in cold water, 3.5% in hot water and 14.7% in a 1% NaOH solution. Burckella wood contains saponin.

Description

Medium-sized to fairly large, laticiferous trees up to 50 m tall; bole columnar or tapering, branchless for up to 25 m and up to 100 cm in diameter, with buttresses up to 2 m high; bark 1-2 cm thick, bark surface greyish-brown with irregular fissures stripping off in small pieces, inner bark fibrous, brown to pale red-brown. Leaves arranged spirally, often crowded at tip of branches, simple and entire, usually obovate, loop-veined with tertiary venation parallel to secondary veins, reticulate or oblique; stipules present or absent. Flowers in fascicles, densely clustered at tips of branchlets in the axils of scale leaves to form a pseudo-terminal inflorescence, bisexual; sepals 4, partially united, strongly imbricate; corolla with tube barbate at throat and 8(-9) imbricate, erect or slightly spreading lobes; stamens 16-18(-30), inserted in 1-2 rows at the top of the corolla tube, with free and geniculate filaments or anthers sessile, anthers extrorse; ovary (3-)4(-5)-locular, hairy or glabrous, often enveloped by an annular or patelliform nectary, style long, exserted. Fruit a large, 1-seeded berry, crowned by the persistent style. Seed usually broadly ellipsoid, sometimes dorsi-ventrally compressed, with very large hilum covering at least half of the seed surface; cotyledons plano-convex, endosperm absent.

Wood anatomy

• Macroscopic characters:

Heartwood pinkish-brown to reddish-brown, occasionally with irregular dark-coloured streaks, not distinctly demarcated from the paler sapwood (yellowish-white when fresh, turning to pale pinkish on exposure). Grain generally interlocked. Texture usually coarse. Growth rings indistinct.

• Microscopic characters:

Vessels diffuse, occasionally with a fairly conspicuous tendency of radial arrangement depending on the species, 12-22/mm², solitary (usually scanty) and in radial multiples of 2-7(-15), 100-200(-230)μm in tangential diameter; perforations simple; intervessel pits alternate, 6-8μm in diameter; vessel-ray and vessel-parenchyma pits often elongated and gash-like and/or palisade-like; tyloses present and distinct. Fibres 890-1820μm long, thick-walled (c. 5μm thick), with numerous slit-like, simple to minutely bordered pits. Parenchyma apotracheal, abundant and forming a reticulate pattern, usually in 1-celled bands. Rays 12-15/mm, 1-2-seriate, (160-)200-1340(-1800)μm high, heterocellular with several rows of square and/or upright cells (Kribs type heterogeneous I-II). Silica bodies numerous in ray cells and scarce in axial parenchyma cells.

Species studied: B. erythrophylla , B. macropoda , B. obovata , B. polymera .

Growth and development

Burckella is a fast-growing light demanding species with a spreading crown.

Other botanical information

Burckella is closely related to Madhuca . It differs from thelatter genus by its pseudo-terminal inflorescence, its partially united sepals, the usually 4-locular ovary, and its very broad seed scar; moreover, it usually has less numerous stamens and a larger fruit.

Ecology

Burckella usually occurs in primary forest in the lowland, in the Moluccas on red-yellow podzolic soils up to 250 m altitude, but in New Guinea up to 1000 m. It is locally common, especially in flood plains in northern Papua New Guinea and the Solomon Islands ( B. obovata ). It thrives in areas with a climatic type B and has been found in association with Homalium foetidum (Roxb.) Benth., Pometia pinnata J.R. Forster & J.G. Forster, Intsia bijuga (Colebr.) O. Kuntze, Canarium spp. and Diospyros spp.

Propagation and planting

In Papua New Guinea, germination of Burckella seed is satisfactory. Wildlings are also used for planting stock production and their development in the nursery is favourable.

Silviculture and management

Regeneration of Burckella in natural forest is profuse. Although it is a light-demanding species, it tolerates shade very well.

Harvesting

In the Solomon Islands the fruits of B. obovata are harvested shortly before they are ripe to prevent damage.

Yield

A log of B. macropoda may yield up to 6.1 m³of timber in New Britain (Papua New Guinea).

Handling after harvest

Green wood has a high moisture content (about 97% in B. macropoda ), and the logs usually do not float in water. The fruits of B. obovata are usually eaten raw, but sometimes they are baked (often "earth baked") which enables short-term preservation. Long-term preservation can be achieved by "pit fermentation", a process commonly used for breadfruit ( Artocarpus spp.).

Genetic resources

Several Burckella species occur very locally (e.g. B. erythrophylla and B. magusum P. v. Royen in New Guinea) and could be easily endangered as a result of indiscriminate logging.

Several cultivars of B. obovata have been recognized in the Solomon Islands based on the shape and taste of the fruits.

Prospects

Very little is known about the ecology and regeneration of Burckella , and there is only limited experience with planting Burckella in Papua New Guinea, apart from cultivation of B. obovata as a fruit tree. Its fast growth and light-demanding character make it a promising plantation species. More research on silvicultural aspects is needed.

Literature

• All Nippon Checkers Corporation, 1989. Illustrated commercial foreign woods in Japan. Tokyo. p. 122.
• Eddowes, P.J., 1977. Commercial timbers of Papua New Guinea. Their properties and uses. Office of Forests, Department of Primary Industry. Port Moresby. pp. 32-33.
• Henderson, C.P. & Hancock, I.R., 1989. A guide to the useful plants of Solomon Islands. Research Department, Ministry of Agriculture and Lands, Honiara. pp. 54-56.
• Lam, H.J., 1932. Enumeration of the Sapotaceae, thus far known from New Guinea. Nova Guinea (Botanique) 14: 549-570.
• Lam, H.J. & van Royen, P., 1952. II. Burckella Pierre. Blumea 6(3): 580-593.
• Peekel, P.G., 1984. Flora of the Bismarck Archipelago for Naturalists. Office of Forests, Division of Botany, Lae. pp. 430-431.
• Pennington, T.D., 1991. The genera of Sapotaceae. Royal Botanic Gardens, Kew & New York Botanical Garden, New York. pp. 160-162.
• van Royen, P., 1957. Revision of the Sapotaceae of the Malaysian area in a wider sense. IIa. Additional notes on Burckella Pierre. Blumea 8(2): 201-203.
• Working group on utilization of tropical woods, 1978. Properties of some Papua New Guinea woods relating with manufacturing processes VI-IX. Bulletin of the Forestry and Forest Products Research Institute, Japan 299: 23-187.
• Working group on utilization of tropical woods, 1980. Properties of some Papua New Guinea woods relating with manufacturing processes X. Bulletin of the Forestry and Forest Products Research Institute, Japan 312: 45-55.