Maheshwar Hegde1, K. Palanisamy1 and Jae Seon Yi2.
Acacia mangium Willd. -
A Fast Growing Tree for Tropical Plantation
1Institute of Forest Genetics and Tree Breeding, R. S Puram, PB 1061 Coimbatore -641002, India
2College of Forest and Environmental Sciences, Kangwon National University, Chuncheon 200-701, Republic of Korea
Taxonomy
Acacia mangium Willd. belongs to Acacia genus, which was originally described as Mangium montanum Rumph in Herbarium Amboinense 3:123, t.81 (1750) but transferred to Acacia by C.L. Willdenow in Sp. Plant 4: 1053 (1806). The specific name is an allusion to Rumphius’ observation that this tree resembled ‘mangge’ or mangroves in Indonesia. Acacia contains 1,200-1,300 species and is divided into three subgenus: Acacia, Aculeiferum and Phyllodinae (Maslin 1995). A. mangium is in Phyllodinae subgenus classed into seven sections, containing more than 900 species (Maslin and McDonald 1996). A. mangium is assigned to section Juliflorae (235 species), a group characterized by having flowers in elongated spikes and numerous phyllodes, often anatomizing by longitudinal nerves. A. mangium may easily be confused with A. holosericea and A. neurocarpa, but it can be readily distinguished by its arborescent habit, glabrous phyllodes and branchlets, white to cream flower spikes and seed with an orange aril (Maslin and McDonald 1996), while other two occur naturally as shrubs or small trees on drier sites.
Distribution
A. mangium has a fragmented natural distribution which stretches from Indonesia (i. e. on the islands of Sula, Ceram, Aru, and Iriyan Jaya), Papua New Guinea (PNG) and north-eastern Queensland in Australia (Fig. 1). The range is 1º-18º-57'S latitudinal and 125°22'-146°17'E longitudinal. The mean altitudinal range is from just above sea level to about 100 m, with an upper limit of 780 m. In Asia, the country with A. mangium natural population distribution is Indonesia. In Oceania, there were Australian Northern Territory, Queensland and Papua New Guinea. A detailed description of the natural distribution and ecology about A. mangium is available in Awang and Taylor (1993) and Krisnawati et al. (2011).
Fig. 1. Generalized range of natural distribution of Acacia mangium.
A. mangium was introduced into many countries. For example, Indonesia and Malaysia have established large-scale plantations for the production of paper pulp. In China, the Philippines, Thailand and Vietnam, the commercial planting of A. mangium is increasing very quickly (Awang and Taylor 1993). Of course, the species has also been introduced to other countries as a plantation tree, such as other Asia countries (Bangladesh, China, Taiwan, India, Indonesia, Laos, Malaysia, the Philippines, Sri Lanka, Thailand, and Vietnam), Africa (Benin, Congo, Cote d’Ivoire, Democratic Republic of Congo, Kenya, Madagascar and Zimbabwe) and Western Hemisphere (Brazil, Costa Rica, Cuba and Hawaii).
Environmental Conditions
Soil
A. mangium is typically a low elevation species chiefly associated with rainforest margins and disturbed sites on well-drained acid soils (pH 4.5-6.5) of low fertility. It also occurs behind mangroves, in seasonal swamps, along streams, and on well-drained flats, low ridges and mountain foot hills (Pinyopusarerk et al. 1993).
Climate
A. mangium distribution area is including the tropical warm and hot climate, either humid or wet zones characterized by a short winter dry season and high total annual rainfall. The mean maximum of the hottest month is about 30-34°C and the mean minimum of the coolest about 15-22°C. It is unsuitable in the area where the absolute minimum temperature falls below 0°C (Yan et al. 1996), so its distribution area is frost-free. In a typical location, the 50% rainfall is 2,150 mm; the 10% is 1,300 mm; and the lowest, on record, is 1,000 mm. It prefers wet sites with an annual rainfall of 1,000-4,500 mm. Prolonged dry periods will slow down the tree growth (Mergen et al. 1983). While the annual rainfall of over 2,500 mm in the Bengkoka/ Kudat region of Sabah is considered adequate for growth. Moreover, it is still affected by seasonal conditions (Pinyopusarerk et al. 1993). During the dry season, when monthly rainfall is below 100 mm and the evaporation rate exceeds 130 mm per month, the tree is under drought stress.
Vegetation types
A. mangium grows on the margins of closed forest (rain forest), in open forest and woodland, especially where there is disturbance by fire. In northern Queensland it occurs in tall forests on well-drained sites of the foothills and lowlands associated with various eucalypts and acacias. As a component of fringing vegetation on river banks, it is frequently associated with rain forest species such as Flindersia brayleyana and Cardwellia sublimis. Elsewhere, it occurs on the slightly better-drained sites within the swampy coastal plains where Melaleuca are locally dominant. Tracey (1982) described the vegetation types in humid, tropical Queensland.
In Papua New Guinea, It occurs in tall woodland and open forest, frequently in mixed associations with other Acacia, Melaleuca and Lophostemon spp. These vegetation types are described by Paijmans et al. (1971), Paijmans (1976) and Skelton (1987). At the western extremity of its range in Indonesia, A. mangium is dominant in small stands on disturbed sites in or on the fringes, closed-forest and Melaleuca spp. woodland.
Botanical Descriptions
Tree morphology
A. mangium is a kind of evergreen tree, up to 30 m tall. The general feature is presented in Fig. 2. The bole can be unbranched for more than half of the total tree height. It is sometimes fluted at the base and the tree diameter rarely exceeds 50 cm. Bark is rough and furrowed, either grey or brown in color. Small branches are winged. It may be reduced to a small tree or large shrub of 7-10 m on unfavorable sites. The bark surface is rough, furrowed longitudinally, and varies in colour from pale grey-brown to brown. The lower bole is sometimes fluted. Detailed botanical description refers to Pedley (1975).
Fig. 2. Feature of Acacia mangium. 1-Habit of young tree; 2-flowering twig; and 3-pods (Source: DFSC seed leaflet).
Leaves (phyllodes)
Borne on very acutely angled, glabrous and stout branchlets, the mature phyllodes of A. mangium are very large, normally 11-27 cm long and 3-10 cm broad. They are dark green, glabrous on a glabrous pulvinus 0.6-1 cm long. The phyllodes are characterized by four (rarely three or five) main longitudinal nerves, basally confluent but distinct from lower margin, minor nerves strongly anatomizing to form a prominent reticulum (Maslin and McDonald 1996). A gland (extra floral nectary) is conspicuous at the base of the phyllode (Fig. 3).
Fig. 3. Phyllode of A. mangium with four longitudinal veins.
Growth phenology
A. mangium is able to grow throughout the year if conditions are suitable. In Thailand, it has been observed that growth appears to slow down or cease in response to the combination of low rainfall and cool temperatures in January-February. Trees start to grow actively again in April before the start of the wet season (Atipanumpai, 1989).
Flowering phenology
Flowering in Acacias is precocious. A. mangium starts to flower and produce seeds 18-20 months after planting (Mergen et al. 1983). Mature fruits occur 3-4 months after flowering period. The time from the onset of flower buds to pod maturity is about 199 days (Zakaria 1993). Flowering phenology differs throughout its natural and planted range. In natural habitat, its flowers are present during February to May in Australia and the seed matures in October-December (Sedgley et al. 1992). Farther north the fruits mature earlier with seed available from July in Indonesia, and late September in Papua New Guinea (Skelton 1987; Turnbull et al. 1983).
As an exotic, the normal flowering cycle may be disrupted and flowering can occur throughout the year. However, a distinct peak is usually discernible (Awang and Taylor 1993). The peak is reported to be June-July in Peninsular Malaysia (Zakaria and Kamis 1991), January in Sabah (Sedgley et al. 1992), October-November in Taiwan (Kiang et al. 1989) and September in Thailand (Kijkar 1992).
Inflorescences, flowers and fruits
The inflorescence consisting of many tiny flowers, occur as rather loose spikes up to 10 cm long, singly or in pairs in the upper axils (Fig. 4). The whitish (or cream) flowers are in rather loose spikes 5-12 cm long on peduncles 0.6-1 cm long, singly or in pairs in the upper axils. The seed pods are linear, tightly coiled when ripe, sometimes tightly spirally coiled, slightly woody, 7-8 cm long and 0.3-0.5 cm wide.
The seeds are black and shiny, longitudinal, ovate to oblong 3-5×2-3 mm with a yellow or bright orange (rarely red) funicle folded to form an oily, fleshy aril beneath the seed (Fig. 4).
Fig. 4. A. mangium inflorescence in blooming stage.
Reproductive Biology and Breeding System
Floral biology
A. mangium flower is regular in symmetry, consisting of five sepals, five petals, numerous stamens and one gynoe-cium. It has a mild and sweet fragrance, which is particularly distinct in the early morning when individual flowers are in boom. (Zakaria 1993). Stigma is non-papillate, measure 63 microns in diameter and forms a cup shaped depression at the tip of style. Stigma and anthers lie in same plane. The anther is bilobed and measures 183 microns. Each lobe has four separate loculi with each loculus enclosing a polyad (Composite pollen grains). The polyad is spherical in shape with diameter of 30-40 microns and each polyad consists of 16 pollens. On an average, there are about 113 stamens per flower. The ovary is sessile, normally with minute hairs, with 12-14 ovules per ovary. Flowers are generally hermaphroditic. However, in some inflorescence staminate flowers are also present (Zakaria and Kamis 1991).
Breeding system
A. mangium is generally an outcrossing species with the tendency toward selfing (Zakaria 1993). In A. mangium andromonoecy-spatial separation of sexes is not prominent. In terms of temporal separation of sexes, protogynous dichogamy is not prevalent. Anthesis occurs very early in the day, with flowers opening in the preceding night at about 21:00 hr. The synchronous emergence of styles and stamens, the immediate anther dehiscence, and stigma receptivity after anthesis signify that the flowers of A. mangium are homog-amous (Zakaria 1993). Zakaria (1993) also found that the species index of self-incompatibility (ISI) rating was 0.38, which could lead it to be classified as an out-crossing species with some degree of selfing despite being partially self-incompatible. Its partial self-incompatibility is probably due to the presence post zygotic lethal genes as in case some other Acacia species.
A. mangium requires biotic agents to transfer pollen from anthers to the stigmas. Pollinators are mainly entomophilic, with Trigona and Apis spp., as the consistent pollen vectors. The most active time of day for these pollinators is between 07:30 and 11:00, after which their activity decreases; and very few pollinators are observed in the day. In spite of dense and conspicuous inflorescence, A. mangium fails to attract a more varied spectrum of pollinators, probably because it lacks floral nectaries (Zakaria 1993).
Hybridization
A. mangium has a chromosome number of 2n = 26 as same as in A. auriculiformis, so it often readily hybridizes with A. auriculiformis. Hybrids of A. mangium × A. auriculiformis 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. Moreover, the hybrid has the straight bole and stem of A. mangium and the self-pruning ability of A. auriculiformis (Zakaria 1993). F1 hybrid trees between A. mangium and A. auriculiformis in Vietnam produced 300-500% greater wood volume than the parental species at 2.5-3 years and at 4.5 years old hybrids, on average, twice the wood volume of A. mangium (Le 1996). Sedgley et al. (1992) found that the cross A. auriculiformis × A. mangium was more successful than the reciprocal, but fertile seed was produced following interspecific pollination in both directions. Vacuum drying of pollen and storage in a deep freeze is recommended for the medium length storage (3 years) of pollen used in crossing programmers of these species (Harbard and Sedgley 1994).
Genetics and Improvement
Initial plantings of A. mangium outside its natural distribution range had generally relied on unimproved materials usually from a narrow genetic base. Consequently, the growth obtained was variable and productivity tended to decline over several generations due to genetic erosion (Awang and Bhumibhamon 1993). Elaborate tree improvement activities are now being taken up in many countries where it has been introduced for production of better planting materials with consistent, desirable characteristics.
Provenance variation
A. mangium has a fragmented natural distribution stretching from the Moluccas islands in Indonesia to Western Province of Papua New Guinea and northeastern Queensland in Australia. Many provenances highly adapted to their natural habitats have been identified and studies have shown variation among them in all respects (Awang and Bhumibhamon 1993). For example, there are large provenance differences in growth rate, stem straightness and frequency of multiple leaders. International provenance trials were established during the 1980s (Doran and Skelton 1982). One of the international provenance trials are shown in Table 1 (Awang and Taylor 1993).
Table 1. A. mangium provenances in the international provenance trials (Awang and Taylor 1993)
Sl. No. | Provenance location (CSIRO seedlot No.) | Provenance region | Lat. (ºS) | Long. (ºE) | Altitude (m) |
1 | Julatten (12990) | Queensland Cairns Region | 16 34 | 145 35 | 400 |
2 | Daintree (12991) | Queensland Cairns Region | 16 17 | 145 31 | 60 |
3 | Rex Range (12992) | Queensland Cairns Region | 16 30 | 145 32 | 30 |
4 | Claudie River (13229) | Far North Queensland | 12 44 | 143 13 | 60 |
5 | Mission Beach (13230) | Queensland Cairns Region | 17 53 | 146 06 | 5 |
6 | NW of Silkwood (13231) | Queensland Cairns Region | 17 42 | 145 57 | 40 |
7 | Cowley Beach (13232) | Queensland Cairns Region | 17 41 | 146 05 | 5 |
8 | NE Walshs Pyramid (13233) | Queensland Cairns Region | 17 06 | 145 48 | 20 |
9 | E of Cairns (13234) | Queensland Cairns Region | 17 02 | 145 48 | 20 |
10 | Mourilayan Bay (13235) | Queensland CairnsRegion | 17 35 | 146 05 | 20 |
11 | Kurrimine (13236) | Queensland Cairns Region | 17 46 | 146 05 | 10 |
12 | El Arish (13237) | Queensland Cairns Region | 17 50 | 146 01 | 20 |
13 | Mission Beach (13238) | Queensland Cairns Region | 17 56 | 146 02 | 70 |