Melia excelsa Jack

Azadirachta excelsa is a large deciduous tree up to 50 m tall, bole up to 125 cm in diameter, buttresses absent. Bark surface smooth, becoming fissured and shaggily flaky, pinkish-brown or pinkish-gray, becoming pale brownish or grayish buff in old trees, inner bark orange-red. Leaves alternate, imparipinnate up to 60(-90) cm long, with 7-11 pairs of leaflets, leaflets asymmetrical, lanceolate to elliptical, up to 12.5 x 3.5 cm, margin entire. Flowers greenish-white, in axillary many-flowered panicles, actinomorphic, 5-merous and fragrant. Fruit drupaceous, 2.4-3.2 cm long, green turning yellow when ripe.

In Thailand A. excelsa flowers from February-March. Fruits, normally eaten by birds and bats, ripen 12 weeks after anthesis.

Preffers alluvial, medium textured, free draining, acidic soils. It is also found growing on clay soils, granite soils; lateritic soils and limestones.

A. excelsa is a plant of lowland monsoon forests in southeast Asia usually occurring in old clearings or secondary forest, but also found in primary dipterocarp forest up to 350 m altitude. It is mostly associated with Durio, Palaquim, Calophyllum and Agathis species.

A. excelsa is native to the Malaysian Peninsular, Sumatra, Borneo, Indonesia and Philippines. No large scale plantation trials have been attempted in Peninsular Malaysia, but there are a number of small experimental trials. The oldest plots with good records are those at the Forest Research Institute, Malaysia, planted in 1953 and 1954. Most other plantings, particularly in Thailand, are very recent. The species has gained in importance as a plantation species due to its fast growth and good timber. However, its unknown genetic base could be a major constraint to the large-scale establishment of plantations.

Root cuttings are possible for industrial scale A. excelsa establishment. This is the best way to guarantee an adequate supply of clonal material from desirable donor trees. Over 90% rooting rates have been obtained when cuttings are taken from coppicing shoots. Rootlets 0.3-0.5 cm diameter and 3-5 cm long have been used successfully in Thailand as propagules. Tissue culture for mass propagation has not been demonstrated to be viable for large-scale seedling production.

The species survives well with almost 100% survival in the field and is relatively free from pest and disease problems during the early growth phase. A. excelsa tolerates greater rainfall than A. indica. Growth is slow initially but subsequently increases significantly. Sentang is planted at a spacing of 2-4 m x 4 m. Harvest of sentang is usually 5 years after planting. Thinning should be done to promote rapid growth and maintain wind firmness. The basis of selection is to choose the dominant leaders, i.e. straight stems and general good form. For medium-size sawlog production, the final crop can usually be achieved after two thinnings. The following thinning regime for A. excelsa has been proposed: first thinning at a mean top height of 10-15 m, stocking greater than 800 stems per hectare is reduced to 500-600 stems per hectare; commercial thinning when the mean top height is 20 m, stocking is reduced to a final crop of 250-300 stems per hectare. Pruning is generally unnecessary, as A. excelsa will self-prune (lower older branches will naturally die and break off).

The sapwood is susceptible to dry-wood termites and powder-post beetles, and also to fungal attacks. Four species of thrips and a moth caterpillar, Loboschiza vulnerata have caused minor damage to plantations in Malaysia.

The germination rate for sentang is 75-80% when seeds are sown directly after harvesting and 50-60% when sown after harvesting. There are 470 seeds/ kg. Fruits should be collected off the trees to avoid contamination by soil borne pathogens and should not be placed directly on the ground. Fruits can be depulped by washing and seeds air dried for 3-7 days in a dry and shaded area before being stored. Density grading by immersion in water can be done, floating seeds should be discarded.

Erosion control: Sentang can be planted for soil conservation purposes. Shade or shelter: A. excelsa is a useful shade provider. Reclamation: The sentang shows potential for plantation establishment and can be used in reforestation and afforestation programmes. Soil improver: The leaves are used in agriculture as mulch. Ornamental: The sentang is a beautiful tree planted in botanical and experimental gardens. Intercropping: A. excelsa is a lesser known tropical fast growing evergreen multipurpose tree of agroforestry potential. Sentang and rubber are often mixed in plantations.

Food: In the Malaysian Peninsular, the young shoots, leaves and flowers are consumed as a vegetable. Apiculture: The fragrant flowers are a source of pollen and nectar. Timber: Sentang is a lightweight to medium-weight hardwood, the heartwood is pale reddish-brown and distinctly demarcated from the yellowish-white, greyish white or sometimes grey-pink sapwood. The wood density is 550-780 kg/cu m at 15% moisture content. Sentang wood is rated as non-durable to moderately durable. The wood is generally easy to work with good boring and planing properties, and takes a good finish. The timber has been used for construction work (joinery, interior finishing and flooring) and for furniture. Its veneer potential is high. Tannin or dyestuff: The tree’s bark contains tannins. Lipids: The seed oil fatty acid composition is: caprylic acid 0.30%, n-capric acid 0.96%, palmitic acid 9.8%, stearic acid 4.7%, heneicosanoic acid 0.72%, behenic acid 2.76%, and tricosanoic acid 0.75%. Poison: The plant parts are insecticidal. The active principle marrangin (azadirachtin L) has multiple effects on the development of insects. Medicine: Seed products of Azadirachta species have been used for a long time in traditional medicine. Other products: The seed oil, with a saponification number 203.38, is used in the manufacture of soap. Marrangin (azadirachtin L) is a natural substance found in sentang with a complex tetranortriterpenoid structure which to date has resisted artificial synthesis.