Fig. 6. Fruits of A. mangium.
Seed storage
The hard impermeable seed coat confers A. mangium seed long viability under almost any conditions if seeds are kept dry and free from insect pests. FAO (1987) recommended storing A. mangium seeds in sealed, air-tight containers in a refrigerator between 0-5°C temperatures. Supriadi and Valli (1988) recommended using clean jerry cans or small jars that could be closed tightly for storing seed. These jars can be stored in a dry, cold storage especially designed for forest tree seeds. This technique has been used to store seeds of A. mangium for several years without serious problems (Adjers and Srivastava 1993).
Dormancy and pretreatment
Germination in A. mangium is inhibited by hard impermeable seed coat. To obtain even and quick germination in nursery, it is necessary to use scarification or some other pretreatment to make the permeable testa being moistened. The most common and practical pretreatment method is the hot water treatment (Adjers and Srivastava 1993). Seeds are pretreated by immersion in boiling water for 30 seconds followed by soaking in cold water for 24 hours alternatively, they can be manually scarified. Germination rate is high (75-90%) after this treatment.
Seed germination and nursery practices
Seeds can be sown in seedbeds, germination trays (wet towel method) or directly in containers. Adjers and Srivastava (1993) gave a detailed description of nursery techniques. The optimum seedling container size for best results is 300 cc. For substratum in container use either top soil mixed with compost or a mixture of tropical peat or rice husk (between 70:30 and 90:10, depending on the characteristic of peat). The optimum height of seedlings for out-planting is 25-40 cm which can be achieved in 12 weeks with proper fertilizer applications. After 3-4 weeks for proper hardening, the seedlings will be ready for planting in 15-16 weeks after sowing in nursery.
Vegetative propagation
A. mangium stem cuttings can be easily rooted if cutting materials from 6 to 12 month-old seedlings are used. Rooting percentage drastically reduced with older planting stocks.
At six-month age of stock plant, rooting percentage was 71% and at 24 months it reduced to 15% (Darus 1993). High air humidity (70-90%) and fairly constant temperature (28°C) required in the rooting chamber. Use of cuttings with one half or one phyllode and applications of auxins such as 500-1,000 ppm IBA or a hormone rooting powder improved rooting. Rooting medium with high pH (5.8-neutral) and high water holding capacity increased rooting (Darus 1993). Micropropagation technique for A. mangium has also been successfully developed and reported. For optimum induction of multiple shoots, Murashige and Skoog basal medium supplemented with 0.5 mg/l of BAP was found to be most suitable (Dams 1993).
Silviculture and Management
Silvicultural characteristics
A. mangium is a fast-growing, sensitive to frost, intolerant of shade and relatively short-lived (30-50 years) tree (Guzman et al. 1997), adapted to a wide range of acidic soils (pH 4.5-6.5) in moist tropical lowlands. In China, It grows slowly when mean monthly temperatures fall below 17°C. While it grows better on fertile sites with good drainage (but not excessively well drained), it will tolerate soils of low fertility and impeded drainage. It is killed by fire only if the stem diameter is less than about 10 cm. The root system is shallow and vigorous. Branches are persistent as the species does not naturally self-prune. Stem heart rot sometimes develops from dead branch stubs. Fluting of the bole is often a problem.
In some locations, A. mangium has a tendency to form multiple stems. The reason of this is not fully understood although it does appear to be partly related to soil fertility, competition, and use of oversized spindly seedlings. Higher phosphate levels and less competition appear to encourage it. Turvey (1995) showed that the number of dominant stems increased as mean tree volume increased, suggesting a relation to conditions favoring faster growth rates. Stem straightness also varies with site fertility where growth is fast (Mead and Miller 1991). It is also very susceptible to typhoon damage in areas prone to high winds such as Hainan Island (China), the Philippines and Vietnam.
Silvicultural practices
Srivastava (1993) has given detailed cases of silvicultural practices for A. mangium in different growing conditions.
Site preparation
The site preparation depends on seven factors-past and present vegetation at planting site, climate, topography, soil type, soil fertility, equipment and labors available. When the logged over forest is to be converted to plantations, clear felling followed by burning is recommended. Disc plowing and harrowing can also be done in grass lands (Srivastava 1993).
Spacing
In Sabah, 3×3 m is the most common spacing for A. mangium. It can also be reduced from 2×2 m to 2.5×2.5 m that is be beneficial to initial fast growth. Some agencies adopted 4×2 m spacing (Srivastava 1993). In Papua New Guinea the most commonly employed spacing is 4x4 m.
Fertilizer application
In China, application of 100 kg/ha N, 50 kg/ha P and 50 kg/ha K resulted in 179% volume production increased at age of 2.6 years for A. mangium (Simpson 1992). The application of suitable fertilizers in adequate amount at the proper intervals has great potential to increase early growth. The type and amount of fertilizer will vary with soil and other site conditions.
Pruning and thinning schedule
A. mangium stands need regular pruning and thinning only if the plantation objective is to produce quality saw logs on a 15-20 year rotation. These operations are not generally done in pulp wood plantations with 6-8 years rotations. Thinning schedule depends on initial spacing, growth rate and end use. Generally, it does not start earlier than 2 years of planting. Second thinning can be done at 4-5 years and third may be at 8-9 years. Although A. mangium shows strong apical dominance, on many sites it tends to develop multiple shoots. This character is controlled by genotype as well site conditions. In Malaysia the standard practice is to remove all shoots besides the leader at 4-6 months after planting. If it is delayed there is a danger of rot fungus entering through large diameter scars (Srivastava 1993).
Coppicing and second rotation
A. mangium stump coppice profusely if a stump hiugher than 50 cm is left. But unlike other species its coppice shoot do not develop into tree size. Therefore, it is not possible to obtain a second rotation by coppicing (Srivastava 1993). In some sites profuse natural regeneration is reported after clear felling.