Acacia mangium Willd. - A Fast Growing Tree for Tropical Plantation

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.

Growth and yield

The considerable amount of information published on the growth of A. mangium confirms that the species can achieve the mean annual increment (MAI) in DBH of up to 5 cm and MAI in height of up to 5 m in the first four or five years. However, growth declines rapidly after seven or eight years, except under very ideal conditions or over long ( 20 years) periods, the tree will probably not grow beyond 35 cm in DBH and 35 m in height (Tsai 1993).

In the studies on this species in Indonesia, growth rate varies considerably with site, age and spacing (Krisnawati et al. 2011). Comparisons can be made on the basis of the mean annual increment (MAI) values. The MAI for diameter ranges from 1.4 to 7.3 cm/year. High DBH MAI values (more than 4 cm/year) are recorded for stands less than 3 years old and after this age the diameter MAI values generally decline towards 1.5-2 cm/year. The MAI for height ranges from 1.8 to 5.8 m/year, and high values of height MAI (more than 4 m/year) have been recorded for stands less than 3 years old, although a height MAI of more than 4 m/year has also been reported in older stands in several sites in Riau and in South Sumatra. As with diameter MAI, height MAI drops, declining towards 2-2.5 m/year. Growth generally declines rapidly after 8 years.

Choice of the correct provenance for a particular planting site can have a major influence on growth rate and yield. On an Imperata grassland site in South Kalimantan and Indonesia, Tuomela et al. (1996) reported there was up to a threefold differences in volume production between the best growing provenances (60-90 m³/ha) and the poorest performers (30-50 m³/ha) at 26 months. In the same study, growth after singling and pruning at 8 months was found to be only about 70% of that of untreated plots. These treatments were deemed by the authors as being undesirable if growth rate is the first priority. In another trial in the same region, Otsamo et al. (1996) reported the MAI for A. mangium at 41 months was up to 39 m³/ha. At Kampar Kiri-Riau, Indonesia, the best provenance in a trial was reported as giving an MAI of 41.4 m³/ha at 2.5 years (Leksono et al. 1996).

In a study conducted in Kerala state in India (Buvane-swaran 2005), the MAI in terms of GBH was worked out for three agro-climatic zones in Kerala and the comparison of the results showed that high altitude zone registered greater MAI in girth (9.6 cm/year) than in southern (8.0 cm/year) and northern zone (9.4 cm/year). Generally, it is observed that within a plantation and within a zone variation in GBH of A. mangium GBH was greater than that of zones in Kerala. However, in humid regions, the productivity ranged from 35 to 45 m³/ha/year particularly in the southern zone of Kerala. On the other hand, in sub-humid climatic condition with red loamy soils as observed in some belt of northern zone, the productivity ranged from 20 to 25 m³/ha/year. A. mangium was observed to be a species for wet zones and hence, localities with long dry spell were not being appropriate for establishing A. mangium plantation. Heart rot / root rot diseases were being risk factors involved in cultivation of Mangium in these dry regions.