|Nitrogen Fixing Trees Highlights (Winrock, 1990-1997, 100 p.)|
Acacia mangium Willd. is one of the major fast growing species used in plantation forestry programs throughout Asia and the Pacific. Due to its rapid growth and tolerance of very poor soils, A. mangium is playing an increasingly important role in efforts to sustain commercial supply of tree products while reducing pressure on natural forest ecosystems.
Acacia mangium is in the family Leguminosae, sub-family Mimosoideae. It has rapid early growth, and can attain a height of 30 meters and a diameter of over 60 centimeters (MacDicken and Brewbaker 1984). Inflorescences are on loose spikes up to 10 cm long with white or cream colored Bowers. When in full blossom, the inflarescences resemble bottle brushes. The flower has a mild, sweet fragrance. The dark green, glabrous phyllodes can be up to 25 cm long and 10 cm broad. The seed pods are broad, linear, irregularly coiled, and up to 3-5 mm wide and 7-8 cm long. The seeds are dark brown to black, shiny, vary in shape, and range from 3-5 mm long and 2-3 mm wide. Seeds mature 6-7 months after flowering (Pinyopusarerk et al. 1993).
Acacia mangium has a chromosome number of 2n=26. Hybrids with A. auiculiformis have the potential to become an important source of planting material for plantation forestry. The hybrid seems to be more resistant to heart rot than A. mangium but tends to be more shrub-like. Moreover, the hybrid has the straight bole and stem of Acacia mangium and the self-pruning ability of A. auicullformis (Tbrahim 1993).
Distribution and Ecology
Acacia mangium is native to Australia Indonesia and Papua New Guinea, but now has a latitudinal range from 19° S to 24° N and a longitudinal range from 88° to 146° E. Acacia mangium is a low-elevation species associated with rain forest margins and disturbed, well-drained acid soils (pH 4.56.5). Altitudinal range is from sea level to about 100 meters, with an upper limit of 780 meters. It is typically found in the humid, tropical lowland climatic zone characterized by a short dry season and a mean annual rainfall between 1446 and 2970 mm. Acacia mangium can tolerate a minimum annual rainfall of 1000 mm. Mean monthly temperatures range from a low of 13-21C and a high of 25-32° C. Though considered an evergreen species, A. mangium does not grow continuously throughout the year. Growth seems to slow or cease in response to the combination of low rainfall and cool temperatures. Dieback occurs during prolonged frost (5-6° C).
When monthly rainfall is below 100 mm, trees exhibit signs of moisture stress (Pinyopusarerk 1993).
Acacia mangium tolerates a soil pH as low as 3.8, and has performed well on lateritic soils with high amounts of iron and aluminum oxides. Acacia mangium has survived on soils with as much as 73% aluminum saturation (Duguma 1995). It is intolerant of saline conditions, shade, and low temperatures. Due to dense foliage, broad phyllodes, and shallow mot system, A. mangium is more susceptible to wind damage than other Acacia species.
Propagation and Silviculture
Although natural regeneration is excellent in clear-felled a' burned fields, nursery propagation is the most common regeneration practice. Hot water treatment for 30 seconds promotes quick seed germination. There are 80,000-100,000 seeds per kilogram. Seed can be sown directly into nurse pots or sown in trays and transplanted to pots aft germination.
Seedlings are retained in the nursery for 12 weeks or until they have attained a height of 25-40 cm. Srivastava (1993) recommends two mot prunings and hardening off of the seedlings before out-planting. In low phosphorus soils in the Philippines, Acacia mangium seedlings fertilized with 30 g/tree of phosphorus showed significant increase in growth compared to seedlings that were not fertilized (Manubag et al. 1995).
Spacing of the seedlings in the plantation depends on the intended uses and soil fertility. Since natural pruning is poor, trees should be planted at close spacing. Plantations cultivated for pulpwood usually have a 4 x 4 m spacing with 830 trees per hectare. For timber production, seedlings planted at 3 x 3 m spacing provide strong lateral competition and fast diameter growth. Seedlings should be planted at wider spacing to produce heavier branches for chipwood and fuelwood (Srivastava 1993). On infertile sites, final stocking should be around 600 700 stems per hectare.
The first weeding should be two months after out-planting. Weeding of noxious plants such as climbers, creepers, and vines is recommended, but less harmful weeds can be left in the field to maintain lateral competition. The number of follow-up weedings will depend upon each site. In areas where Imperata has a stronghold, weedings should be frequent.
Pruning schedules also depend on intended use. In agroforestry systems branches are pruned regularly to prevent competition with agricultural crops. To produce quality sawlogs, all branches below the height of 6 meters should be pruned regularly. These branches must be pruned before becoming 2 cm in diameter to avoid fungal infections (Srivastava 1993).
On degraded Imperata grasslands, Otsamo et al. (1995) observed that A. mangium had a mean annual volume increment of 10 m³/ha/year. In a 15-year rotation, precommercial thinning should occur at 24 months, followed by a thinning at 36 months Per this schedule, volumes are between 290 and 439 m³/ha after ten years' growth.
Acacia mangium has a wood density ranging from 420 to 600 kg/m³ and a specific gravity of 0.65 (MacDicken and Browbaker 1984). Due to ease of drilling and turning, it is a popular wood for furniture, agricultural implements, crates, particle board, and wood chips. Acacia mangium is also suitable for manufacturing charcoal briquettes and activated carbon. It has a calorific value of 4,8004,900 Kcal/kg. Acacia mangium's susceptibility to heart rot limits its use for sawn timber, but it is a common pulp and paper crop in Sumatra, Sabah and Vietnam. Nontimber uses include honey production, adhesives, and as an ornamental and shade tree for roadsides or other urban forestry uses. Acacia mangium sawdust provides good-quality substrate for shiitake mushrooms.
Since A. mangium can grow on marginal soils, many farmers choose to plant this species to improve soil fertility of fallowed fields or pastures. Since trees with diameters of 7 cm are fire resistant, Acacia mangium plantations can be used as fire breaks.
Highly effective Rhizobium strains have been identified for Acacia mangium (de Faria 1995). Acacia mangium teas a relationship with some VAM fungi including Thelephora ramariods, Gigaspora margarita, Glomus etunicaturm, and Scutellispora calospora.
Pests and Diseases
The major pests associated with A. mangium cause damage to seedlings, branches and stems, or wilting caused by root damage. Damage does not result in death, but may deform or suppress tree growth (Hutacharem 1993).
Most disease agents of A. mangium are associated with or caused by fungi. Common disease symptoms are damping off, heart rot, powdery mildew, stem galls, dieback, leaf spots, and root rot (See 1993).
Duguma, B. 1995. Growth of nitrogen fixing trees on moderate to very acid soils of the humid lowlands of southern Cameroon. In Evans D. 0. and LT. Szott eds. Nitrogen Fixing Trees For Acid Soils. Proceedings of Workshop m Turrialba, Costa Rica, July 3-8 1994: Winrock International and CATIE. pp. 195-206.
Faria S. M. de. 1995. Occurrence and rhizabial selection far legume trees adapted to acid soils. In Nitrogen Fixing Trees For Acid Soils. pp. 295-301. See Duguma 1995.
Hutascharem, C. 1993. Chapter 9: Insect pests. In Awang K and D. Taylor eds. Acacia mangium Growing and Utilization. MPTS Monograph Series No. 3. Bangkok. Thailand Winrock International and FAO. pp. 163-203.
Ibrahim, Z. 1993. Chapter 2: Reproductive biology. In Acacia mangium Growing and Utilization pp. 21-34. See Hutacharem 1993.
MacDicken, K and J. L. Brewbaker. 1984. Descriptive summaries of economically important nitrogen fixing trees. NFT Res. Rpts. 2:46-54.
Manubag J. B. Laureto J. Nicholls. and P. Canon. 1995. Acacia mangium response to nitrogen and phosporus in the Philippines. In Acacia mangium Growing and Utilization. pp. 32-35. See Duguma 1995.
Pinyopusarerk K. S.B.Liang, and B.V.Gum. 1993. Chapter 1: Taxonomy distibution, biology and uses as an exotic. In Acacia mangium Growing and Utilization pp. 1-20. See Hutacharem 1993.
Otsamo, A. G. Adjer, T. S. Hadi J. Kuusipado K Tuomela, and R. Vuokkko. 1995. Effect of site preparation and initial fertilization on establishment and growth of four plantation trees species used in reforestation of Imperata cylindrica (L.) Beauv. dominated grasslands. For. Ecol. and Mgmt. 73:271-m.
See L S. 1993. Chapter 10: Diseases. In Acacia mangium Growing and Utilization pp. 203-238. See Hutacharem 1993.
Srivastava P.B.L 1993. Chapter 7: Silvicultural practices. In Acacia mangium Growing and Utilizatzon.pp. 113- 147. See Hutacharem 1993.
FACT 96-05 September 1996