Acacia nilotica (gum arabic tree)
Datasheet Types: Tree, Invasive species, Host plant
Abstract
This datasheet on Acacia nilotica covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Genetics and Breeding, Economics, Further Information.
Identity
- Preferred Scientific Name
- Acacia nilotica (L.)
- Preferred Common Name
- gum arabic tree
- Other Scientific Names
- Acacia adansonii Guill. & Perr.
- Acacia adstringens (Schumach.) Berhaut
- Acacia arabica (Lam.) Willd.
- Acacia arabica var. nilotica (L.) Benth.
- Acacia indica Benth.
- Acacia scorpioides W. Wight
- Acacia scorpioides var. nilotica (L.) A. Chev.
- Mimosa arabica Lam.
- Mimosa nilotica L.
- Mimosa scorpioides L.
- Vachellia nilotica P.J.H. Hurter & Mabb.
- International Common Names
- EnglishArabic gumtreebabul acaciablackthornEgyptian mimosaEgyptian thornprickly acaciaprickly mimosascented thornscented-pod acacia
- Spanishacacia gomifera
- Frenchacacia a gommeacacia d'Arabieacacia de Cayennegommier rouge
- Arabicgarad-sunt
- Local Common Names
- amrad gum
- Angolaongue
- Bangladeshbabla
- Botswanalekwele
- Cameroonbagani-iribanibaranaboinadaibegabdegabderegabdi
- Cape Verdeespinheiro pretoespinho preto
- Ethiopiafulissa
- GermanyArabische AkazieGummi - Akazie
- Guinea-Bissaubanogaude
- Indiabablababoulbabuldauriagodigodi babulkabuli kikarkaorakauliakauriakavadikikarkikkarram babulramkantaramkati babulteli babulteliatelia babulvedi
- Italyacacia d'Egitto
- Kenyaakurukukuburgugeburkukehburquqechalabduchebitetchebiwachigundigundiekapelimenkisemeikopkwomgundimgungamjungumsemerimtetewemungamusemeingobgwaokopkwool-kilorititwerrugunzayakapelimen
- Lesser Antillesblack piquantcashacassie
- Libyagarrad
- Malawichiwiririkawililinamalenganamalingangalankanga
- Malibaganatehedjeit
- Mozambiquechanguachiciachissivem'siomunhetchissio
- Namibiaeno
- Nigeriabaggarua
- Pakistanramkanthi
- Puerto Ricogoma de acacia
- Senegalgonakieneb goalie
- Somaliamarahtugaar
- South Africatshungapandaumgawe
- Sudanasit
- Tanzaniabariomotbarjomoddubiloelaraiisejelekichachakiloritikinjachakizamila'akomanangemgungamwiya kimbundubirongeregereolgiloritiolgoreteumsasau
- Ugandakapuka
- Yemenosdi
- Zambiamunganunchi
- Zimbabweisanqawemuongamuunga
Pictures
Flowers and foliage
Acacia nilotica (gum arabic tree); Flowers, open and unopened and foliage. Karnak, Egypt.
©A.R. Pittaway
Flowers
Acacia nilotica (gum arabic tree); Open and unopened flowers. Karnak, Egypt.
©A.R. Pittaway
Seedpod
Acacia nilotica (gum arabic tree); Ripe seedpod. Karnak, Egypt.
©A.R. Pittaway
Seedpod
Acacia nilotica (gum arabic tree); Close-up of ripe seedpod. Karnak, Egypt.
©A.R. Pittaway
Flowers
Acacia nilotica (gum arabic tree); Flowers of subsp. adstringens are arranged in bright yellow orange globose inflorescences, such as this shoot. Burkina Faso.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
Pods
Acacia nilotica (gum arabic tree); Green, indehiscent pods of ssp. leiocarpa, which turn black when mature. Kenya.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
Lopping for fodder
Acacia nilotica (gum arabic tree); subsp. indica being lopped for fodder. nr. Jaipur, Rajasthan, India.
©Colin Hughes/OFI (Oxford, UK)
Fodder and shade tree
Acacia nilotica (gum arabic tree); Fodder and shade from subsp. kraussiana are vital in the hot dry season. Chivu, Zimbabwe.
©R.D. Barnes/OFI (Oxford, UK)
Habit
Acacia nilotica (gum arabic tree) subsp. cupressiformis, planted in Rajasthan, India.
©Colin Hughes/OFI (Oxford, UK)
Windbreak
Acacia nilotica (gum arabic tree); subsp. cupressiformis, planted along field boundaries as windbreaks. Pali, Rajasthan, India.
©Colin Hughes/OFI (Oxford, UK)
Habit
Acacia nilotica (gum arabic tree); a Young bush of subsp. adstringens. Burkina Faso.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
Flowering
Acacia nilotica (gum arabic tree); The rounded crown of subsp. leiocarpa is beginning to bloom on the coast of Kenya.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
Plantation
Acacia nilotica (gum arabic tree); subsp. tomentosa stand planted on a 30 year rotation for timber on the Blue Nile floodplain nr. Dinder, Sudan.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
Avenue planting
Acacia nilotica (gum arabic tree); subsp. indica planted as an avenue tree in India.
©Chris Fagg, Depto. Ecologia, Univ. Brasilia
A. nilotica subsp. indica and Products
Acacia nilotica (gum arabic tree); Wood provides high quality charcoal, firewood, and bark for tannin production. Punjab State, India.
©Colin Hughes/OFI (Oxford, UK)
Overview
Importance
Acacia nilotica is a pioneer (light-demanding), nitrogen-fixing tree, and is relatively fast growing on arid sites. It is an important riverine tree in India, Sudan and Senegal, where it is planted for timber. It has long been one of most popular farm trees throughout the Indian subcontinent for its many uses (timber, fuelwood, fodder, tannins and gum) and ease of propagation.
It is used extensively for rehabilitation of degraded saline and alkaline soils, and as a windbreak or avenue tree. It has a strategic value providing forage resources in many pastoral systems in Africa.
Being a prolific seeder and thorny, it can form thickets and become invasive, particularly in more humid sites or where it is not heavily utilized. More research is needed on evaluating genetic variation and on farm spacing trials to investigate thicket formation.
Summary of Invasiveness
Acacia nilotica is tolerant of grazing, drought, fire, saline soils and is a prolific producer of seeds, which through long viability are able to accumulate in the seedbank. This species produces large quantities of seeds that are dispersed by animal, water and wind and can remain dormant in the soil for long periods. It fixes nitrogen and is a useful protein supplement for grazing animals in agroforestry systems. Poor management has led to major invasions in Australian rangelands and it is also known to demonstrate invasive behaviour in other countries including some within its native range. A. nilotica is a valuable tree in the majority of its existing range; further introduction to other countries where it is not yet present is not recommended.
Taxonomic Tree
Notes on Taxonomy and Nomenclature
Acacia nilotica is one of about 130 African species of Acacia, belonging to the subfamily Mimosoideae of the legume family (Fabaceae). These differ significantly from the Australian acacias in being armed with thorns and producing highly palatable pods. The International Code of Botanical Nomenclature ratified the reclassification of Acacia in 2011, restricting the genus Acacia to the Australian species (about 900 species) and placing Acacia nilotica in Vachellia as Vachellia nilotica (L.) P.J.H. Hurter & Mabb. (Kyalangalilwa et al., 2013). However, for the purposes of this datasheet the name Acacia nilotica will be used pending a comprehensive revision of all compendium datasheets to correct the taxonomy of this genus.
Acacia nilotica is generally accepted as a single, extremely variable species, divided into nine subspecies, three occurring in the Indian subcontinent and six throughout Africa (Brenan, 1983). The subspecies are distinguished by shape, size and degree of pubescence on the pods and the degree of pubescence on the branchlets. Shape of crown and habit are also important in distinguishing the subspecies.
The three Asian subspecies, as described by Troup and Joshi (1983), are: (1) A. nilotica subsp. indica, known as telia babul, teli or godi, the most common, economically important and extensively grown subspecies, with a spreading crown, bright brown shoots, smooth bark and short, slender (and relatively few) spines; (2) A. nilotica subsp. subalata (also common in East Africa), known as vedi, kaora or kauria babul, which is smaller than (1), with a shorter stem, a more spreading crown, more twisted and interlaced branches than (1), a greyish-brown bark, stouter, whiter and longer spines and flat pods which are a little constricted between the seeds - it is more common in the Deccan region; and (3) A. nilotica subsp. cupressiformis, known as ramkanta or kabuli kikar, identified by its characteristic long, thin crown form which produces an inferior wood (see also Luna, 1996).
The pattern of variation is not very clear in certain regions, with some of the African subspecies possibly occurring in Asia (A. nilotica subsp. subalata and A. nilotica subsp. adstringens) (Brenan, 1983) and A. nilotica subsp. kraussiana appearing to have a disjunct distribution both in southern Africa and Ethiopia and Arabia (Miller and Morris, 1988; Hedberg and Edwards, 1989). Ali and Qaiser (1980) suggest that the African subspecies may have arisen in Asia through hybridization of A. nilotica subsp. indica and A. nilotica subsp. hemispherica, although these parents do not naturally occur there. The problem is that specimens without pods are not easily attributable to a subspecies. A. nilotica subsp. cupressiformis varies little from A. nilotica subsp. indica except in its habit (it has the shape of a poplar); seed from trees of A. nilotica subsp. cupressiformis produce a 3:1 ratio of cupressiformis: indica seedlings (C Hughes, D Hocking, personal communications).
Plant Type
Perennial
Seed / spore propagated
Broadleaved
Shrub
Tree
Woody
Description
Acacia nilotica is generally a single-stemmed tree, usually 2.5-15 m high but can reach 25 m or more in riverine subspecies. The crown can be upright and flattened or rounded and spreading, as well as varying from hemispherical to narrow and erect. In India, stem circumference can reach 2-3 m, with a clear bole height of 6-7.5 m (Troup and Joshi, 1983). The bark is grey to brownish-black, rough and longitudinally fissured, never powdery or peeling. Young branchlets glabrous to subtomentose, glands inconspicuous or absent, bark not flaking off.
Acacia nilotica is distinguished from most African Acacia species in possessing long, straight, paired thorns at the leaf axil which are characteristically deflexed. It forms a deep and extensive root system on dry sites, the tap root developing first and then the laterals, which become compact and massive, but on flooded sites the root system is largely lateral. The alternate bipinnate leaves can be glabrous to subtomentose; petiole 0.4-2.5 cm long with an adaxial gland (sometimes 2) often present; rachis 1.2-8 cm long, with a gland at the junction of each pinna pair or top few pairs only; pinnae 2-14 pairs, leaflets 7-36 pairs per pinna, 1.5-7 x 0.5-1.5 mm, glabrous to pubescent, lateral nerves not visible beneath. Bright or golden yellow, sweetly scented, numerous, with bisexual and male flowers on the same globose inflorescence. Flowering is prolific, can occur a number of times in a season on current seasons growth, but often only about 0.1% of flowers set pods (Tybirk, 1989). Stamen filaments are free, glandular, 5-6 mm long. The involucel (small pair of bracts) occurs from near the base to over halfway up the peduncle (inflorescence stalk) and sometimes has a few sterile flowers developing from it. These are very variable depending on the subspecies, indehiscent with varying thickness, dark brown to grey, straight or curved, glabrous or velvety, 4-22 x 0.9-2.2 cm, margins entire or deeply constricted between each seed (for the African varieties, not the Indian/Asian varieties), the position of each seed clearly marked by a distinct raised bump in the pod valves. Seeds are 6-17 per pod, 6.5-9 x 5-8 mm, dark brown to brownish black, elliptic to subcircular; areole 5-7 x 4-7 mm, 'U'- or closed ‘O’-shaped.
Distribution
Acacia nilotica is naturally widespread in the drier areas of Africa, from Senegal to Egypt and southwards to South Africa (Natal) and through the Middle East to Asia as far eastwards as India and Bangladesh. Houerou (1988) collated information on the distribution of the various subspecies and reports depletion of native A. nilotica forests in Senegal, Niger and along the River Nile due to over-exploitation and man-made changes to the water table and flooding regimes. In Pakistan, some areas of riparian A. nilotica forests are being invaded by the introduced Prosopis juliflora (IUCN, 2000). Currently, A. nilotica can be found naturalized and cultivated in Asia, Australia and the Caribbean (ILDIS, 2015; PIER, 2015; USDA-ARS, 2015).
In some of its native range countries, A. nilotica appears to demonstrate invasive behaviour (Holm et al., 1979; Carter, 1998); however, these records are likely to refer to introduced subspecies, such as A. nilotica subsp. indica in East Africa.
Distribution Map
Distribution Table
History of Introduction and Spread
Acacia nilotica has been widely introduced and cultivated, including in parts of the Indian subcontinent and Pakistan (where it is not native), in the Caribbean, Australia, Cyprus, Israel, Tanzania (Zanzibar), Cape Verde, Iraq, Indonesia (Java, Lesser Sunda Islands), Vietnam, Nepal and Iran. It is also planted within its native range, such as in Sudan, Egypt, Tanzania and Nigeria, principally for timber and fuelwood, tanning, fodder and shade and in the Indian subcontinent for fuelwood and timber, agroforestry, land rehabilitation and many other uses, though there is a possibility that non-native subspecies have sometimes been introduced.
The pioneer characteristics of A. nilotica, often on overgrazed lands, result in an invasive propensity and the formation of thorny thickets (Wells et al., 1986) and it has become a major weed in Australia and Java, Indonesia (Carter, 1994). According to Weber (2003), it is the subspecies indica that has caused problems in Australia. This was introduced to Australia around 1900 and was declared a noxious weed in 1957 (Carter, 1998); it is now a notifiable weed with varying degrees of restriction and control in the states of New South Wales, Western Australia, South Australia, Tasmania and Northern Territory (Anon., 1998). The worst infestations are in Queensland, but are also known from the Northern Territory, New South Wales and South Australia (Carter, 1998). Planting patterns (along water drainage channels) and stock management have contributed to the spread of A. nilotica in Queensland (Carter, 1998) since trees adjacent to water have higher rates of reproductive success and livestock are able to disperse the seeds via their dung to non-infested areas. According to Radford et al. (2001) the pattern of spread is uneven across the landscape with higher levels of seedling recruitment and hence, thicket formation predicted next to watering points and other locations that attract cattle, the prime dispersers of seed in Australia.
Binggeli (1999) classified A. nilotica as a highly invasive species. According to Holm et al. (1979), it is a serious weed in Mozambique, a common weed in Kenya, a weed of unspecified importance in Australia and present in the flora of Swaziland. The same source lists the species’ synonym A. arabica as a serious weed in South Africa and a weed of unspecified importance in India, Pakistan and Sudan. In the Caribbean, A. nilotica appears in herbaria collections made as early as 1883 in Martinique, 1889 in Grenada and 1904 in Jamaica (US National Herbarium). A. nilotica is currently listed as invasive in Puerto Rico, Cuba, Antigua, Barbuda and Anguilla (Kairo et al., 2003; Rojas-Sandoval and Acevedo-Rodríguez, 2015).
Risk of Introduction
Acacia nilotica should not be introduced into humid and subhumid areas, or into dry areas where there are adequate supplies of grazing and fuelwood. The risk of invasion appears high where both a good water supply to promote high seed production and the presence of domestic livestock, particularly cattle, to disperse seeds, are available. The wide-scale existing distribution of the species means that there are countries where the risk will be associated with existing introduced populations, which should be monitored for signs of invasive behaviour.
Means of Movement and Dispersal
Natural Dispersal
Water and wind disperse some of the seeds (Carter, 1998). Flood water can contribute to long distance abiotic seed dispersal (Carter, 1998). The presence of A. nilotica along water courses and spread following flooding events confirm that water may be a significant means of seed dispersal both in its native range and where introduced.
Vector Transmission (biotic)
Mammals disperse the seeds of A. nilotica (Weber, 2003) and this is the primary dispersal mode in Australia where the species is invasive (Anon., 2001). The nutritious, indehiscent seed pods have evolved for animal dispersal. Vectors include cattle, sheep, goats, camels, impala, Thompson's gazelle, dorcas gazelle, dikdik, elephant, giraffe [Giraffa camelopardalis], kudu [Tragelaphus strepsiceros] and mountain goat (Carter, 1998). If livestock that have eaten seeds are transported by road vehicles, the potential distance over which seeds are dispersed is very large (Carter, 1998). In cattle, the dispersal mechanism is through the gut, after the seeds have been swallowed, whereas in sheep and goats the mechanism is via the regurgitation of seeds (Anon., 2001). Seeds may also be transported in mud stuck to animal hooves (Anon., 2001).
Agricultural Practices
Planting patterns (along water drainage channels) and stock management have contributed to the spread of A. nilotica in Queensland, Australia (Carter, 1998), since trees adjacent to water have higher rates of reproductive success and livestock are able to disperse the seeds in dung to non-infested areas. Carter (1998) associates the most severe infestations with cattle (as opposed to sheep) ranching.
Accidental Introduction
Seeds may be accidentally dispersed to non-infested areas when they are transported in the gut of cattle that have fed on pods and so a period of quarantine, to allow stock to evacuate seeds, is recommended prior to livestock release in new grazing land (Anon., 2001).
Intentional Introduction
Acacia nilotica has been widely introduced to countries across Asia, Australasia, Central and South America and the Pacific for the many acknowledged uses that this species is accepted as having.
Pathway Causes
| Pathway cause | Notes | Long distance | Local | References |
|---|---|---|---|---|
| Animal production (pathway cause) | Cultivated in agroforestry systems to be used as forage and fodder | Yes | Yes | |
| Disturbance (pathway cause) | Escaped from cultivated areas | Yes | Yes | |
| Escape from confinement or garden escape (pathway cause) | Agroforestry system | Yes | Yes | |
| Forage (pathway cause) | Cultivated in agroforestry systems to be used as forage and fodder | Yes | Yes | |
| Forestry (pathway cause) | Cultivated in agroforestry systems | Yes | Yes | |
| Habitat restoration and improvement (pathway cause) | Used as a pioneer species in land rehabilitation and as a barrier to desertification | Yes | Yes | |
| Horticulture (pathway cause) | Cultivated in agroforestry systems | Yes | Yes | |
| Nursery trade (pathway cause) | Cultivated in agroforestry systems | Yes | Yes | |
| Ornamental purposes (pathway cause) | Cultivated in agroforestry systems | Yes | Yes |
Pathway Vectors
| Pathway vector | Notes | Long distance | Local | References |
|---|---|---|---|---|
| Debris and waste associated with human activities (pathway vector) | Cultivated in agroforestry systems | Yes | Yes | |
| Machinery and equipment (pathway vector) | Seeds | Yes | Yes | |
| Livestock (pathway vector) | Seeds | Yes | Yes | |
| Soil, sand and gravel (pathway vector) | Seeds | Yes | Yes | |
| Water (pathway vector) | Seeds | Yes | Yes | |
| Wind (pathway vector) | Seeds | Yes | Yes |
Habitat
Acacia nilotica prefers semi-arid, warmer temperate and subtropical regions but is also found in tropical environments and will grow near water sources in arid areas. It is most commonly found growing in grasslands, pastures, open woodlands, floodplains, open plains, recently cleared land, near stockyards and farm buildings and along roadsides. It is a pioneer species that is relatively fast growing on arid sites. A. nilotica is an important riverine tree in India, Sudan and Senegal, where it is planted for timber. Houerou (1988) describes native range habitat types for several subspecies, tomentosa, adstringens and nilotica. These are all described in the context of flood plain or water course habitats with varying degrees of flooding. According to Weber (2003), A. nilotica invades grasslands and savanna habitats. In Queensland, Australia, it has invaded plains of Mitchell grass (Astrebla spp.), occurring on soils with a high clay content and sandy loams providing there is sufficient moisture, waterways and seasonally flooded plains including saline areas (Carter, 1998).
Habitat List
| Category | Sub category | Habitat | Presence | Status |
|---|---|---|---|---|
| Terrestrial | Managed forests, plantations and orchards | Present, no further details | Harmful (pest or invasive) | |
| Terrestrial | Managed forests, plantations and orchards | Present, no further details | Natural | |
| Terrestrial | Managed forests, plantations and orchards | Present, no further details | Productive/non-natural | |
| Terrestrial | Terrestrial – Managed | Managed grasslands (grazing systems) | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial – Managed | Managed grasslands (grazing systems) | Present, no further details | Natural |
| Terrestrial | Terrestrial – Managed | Managed grasslands (grazing systems) | Present, no further details | Productive/non-natural |
| Terrestrial | Terrestrial – Managed | Disturbed areas | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial – Managed | Disturbed areas | Present, no further details | Natural |
| Terrestrial | Terrestrial – Managed | Rail / roadsides | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial – Managed | Rail / roadsides | Present, no further details | Natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Natural grasslands | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Natural grasslands | Present, no further details | Natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Natural grasslands | Present, no further details | Productive/non-natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Riverbanks | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Riverbanks | Present, no further details | Natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Riverbanks | Present, no further details | Productive/non-natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Scrub / shrublands | Present, no further details | Harmful (pest or invasive) |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Scrub / shrublands | Present, no further details | Natural |
| Terrestrial | Terrestrial ‑ Natural / Semi-natural | Scrub / shrublands | Present, no further details | Productive/non-natural |
Biology and Ecology
Genetics
Acacia nilotica shows a great deal of morphological variation, nine subspecies being recognized (Brenan, 1983), indicative of high levels of genetic variation. It is an outcrossing, insect-pollinated species and the taxa form a polyploid complex: most are tetraploids (2n = 52); but higher numbers have been found in A. nilotica subsp. nilotica (2n = 104) and A. nilotica subsp. tomentosa (2n = 208) (Nongonierma, 1976). The mating system of A. nilotica was investigated by scoring three enzyme systems in starch-gel electrophoresis, isozyme banding patterns within families suggesting that the species is autotetraploid, displaying tetrasomic inheritance. The best level of outcrossing was tm=0.384, highly significantly less than one. These suggested that the species is self-compatible and approximately 60% of seeds are set through self-pollination (Mandal et al., 1994). Controlled pollinations are needed to estimate the degree of compatibility and assessing the factors controlling the extent of outcrossing in this species, otherwise heritability will be overestimated from open pollinated progeny trials.
A number of early trials were based on relatively few collections. Plant material was collected and planted in a FAO/IBPGR project for arid zone species (Armitage et al., 1980), but again sampling was from relatively few sites. More recently, range wide collections in Africa were undertaken by the Oxford Forestry Institute (now the Department of Plant Sciences), UK and members of the African Acacia trials network (comprising OFI, UK, CIRAD-Forêt, France and the Danida Forest Seed Centre, DFSC, Denmark), co-ordinated by the FAO and seed is available for trials (Fagg et al., 1997). There have been a number of international provenance trials planted but these have yet to be evaluated. In India, large provenance trials of A. nilotica subsp. indica have been planted and data on germination, seedling growth and nitrogen fixation are available (Toky et al., 1995; Krishan and Toky, 1996).
Reproductive Biology
A mature tree can produce 2000-3000 pods in a good fruiting season, each with usually between eight and 16 seeds, yielding 5000 to 16,000 seed/kg depending on the subspecies. The species will produce pods in abundance after 5 to 7 years of age. There is considerable variation in the degree of seed production and germination in relation to water supply, with high reproductive success recorded in very wet years or in favourable locations, e.g. next to water channels (Carter, 1998). Trees adjacent to water are able to reproduce in most years (Anon., 2001) but trees in dry areas produce few seeds in the absence of winter rain (Carter, 1998). Seeds are dispersed by mammalian herbivores, particularly domestic livestock and a high proportion of the seeds that pass through stock are viable (Carter, 1998) and seeds may remain viable for 7 years or more (Anon., 2001).
Physiology and Phenology
Acacia nilotica flowers at a relatively young age, around 3 to 4 years of age, in ideal conditions, on current-season growth during the rainy season. Flowering is prolific and can occur several times a year depending on the availability of soil moisture. In southern Africa (all countries south of Tanzania), peak flowering appears to occur from October to December and peak fruiting around April/June. In eastern Africa, the trend is complicated by bimodal rainfall, with flowering occurring most months of the year for subsp. subalata with no marked fruiting period, although flowering of subsp. leiocarpa tends to peak in September (Fagg and Barnes, 1995). In West Africa, in subsp. adstringens flowering occurs over most of the year with a peak in October; in subsp. nilotica flowering peaks in September/October; and in subsp. tomentosa a little later in November. Fruiting peaks in January for subsp. adstringens and subsp. tomentosa and in April for subsp. nilotica. In India, subsp. indica flowers from June to September and sometimes in December/January and the pods reach full size (for fodder) by February/March and ripen from April to June (Gupta, 1993).
Associations
Acacia nilotica is a nitrogen-fixing tree that nodulates frequently over its natural range and forms mycorrhizal associations (Njiti and Galiana, 1996; Ingleby et al., 1997).
Environmental Requirements
Acacia nilotica prefers dry conditions, with an annual rainfall of 200-1500 mm, although under irrigation some varieties will grow in areas with less than 100 mm. In India, the optimum lower limit is around 600 mm without irrigation (Troup and Joshi, 1983) and there are records of upper limits of 2300 mm in South East Asia (Lemmens and Wulijarni-Soetjipto, 1991). Some of these are plantings out of its natural range and caution is recommended before making introductions into humid areas. It is found principally in the drier lowland tropical and subtropical regions, in both unimodal and bimodal rainfall regions and in regular and irregular regimes (Nicholson et al., 1988). Average annual temperatures commonly vary from 15° to 28°C, although it can withstand daily maximum temperatures of 50°C and is frost tender when young. Depending on the subspecies, it will tolerate both drought and flooded conditions for several months. A modified description of climatic requirements (see climatic data table of this data sheet) was prepared by CSIRO (Booth and Jovanovic, 2000).
Acacia nilotica in Africa exhibits two very distinct ecological preferences: subspecies subalata, leiocarpa and adstringens occur in wooded grassland, savanna and dry scrub forests on deep sandy loamy soils and also on lateritic and calcareous sites; subsp. kraussiana also prefers dry grasslands and savannas, especially on compacted sandy loam, shallow granite or clay soils along drainage lines and rivers, but away from flooding. On the other hand, subsp. nilotica and tomentosa are restricted to riverine habitats and seasonally flooded areas on clay alluvial soils (Fagg, 1992). In the Indian subcontinent, subsp. indica forms low altitude dry forests usually on alluvium soils subject to flooding or black cotton soils. It is now widely planted on farms throughout the plains and will grow on saline, alkaline soils and on those with calcareous pans, but requires sufficient moisture in the soil or subsoil (Troup and Joshi, 1983; Luna, 1996). It will grow but remain stunted on shallow soils with an underlying bedrock or beds of nodular kankar and also on poor argillaceous soils. A. nilotica subsp. hemispherica is restricted to sandy stream beds near Karachi, Pakistan and subsp. cupressiformis has similar preferences to subsp. indica, though it is less resilient to weed competition. In the Indian subcontinent, A. nilotica is usually found below altitudes of 450 m although some subspecies in Africa occur at altitudes as high as 2000 m.
Vegetation Types
bottomland forests
coastal plant communities
dry forests
riparian forests
savanna woodlands
savannas
secondary forests
thicket
wetlands
Latitude/Altitude Ranges
| Latitude North (°N) | Latitude South (°S) | Altitude lower (m) | Altitude upper (m) |
|---|---|---|---|
| 32 | 30 | 0 | 2000 |
Air Temperature
| Parameter | Lower limit (°C) | Upper limit (°C) |
|---|---|---|
| Absolute minimum temperature | -1 | |
| Mean annual temperature | 15 | 28 |
| Mean maximum temperature of hottest month | 25 | 42 |
| Mean minimum temperature of coldest month | 6 | 23 |
Rainfall
| Parameter | Lower limit | Upper limit | Description |
|---|---|---|---|
| Dry season duration | 5 | 10 | number of consecutive months with <40 mm rainfall |
| Mean annual rainfall | 200 | 2200 | mm; lower/upper limits |
Rainfall Regime
Summer
Winter
Bimodal
Uniform
Soil Tolerances
Soil texture > light
Soil texture > medium
Soil texture > heavy
Soil reaction > acid
Soil reaction > neutral
Soil reaction > alkaline
Soil drainage > free
Soil drainage > impeded
Soil drainage > seasonally waterlogged
Special soil tolerances > shallow
Special soil tolerances > saline
Special soil tolerances > sodic
Special soil tolerances > infertile
Soil Types
acrisols
alkaline soils
alluvial soils
arenosols
arid soils
calcareous soils
cambisols
clay soils
ferralsols
gleysols
lateritic soils
luvisols
regosols
saline soils
sandy soils
vertisols
Notes on Pests
A wide range of pests and diseases attack living A. nilotica trees, but none limit their cultivation; there are reviews in Browne (1968), Roberts (1969), Mohyuddin (1981), Sheikh (1989) and Brunck (1994).
Diseases
The most important fungi are Fusarium oxysporum, which causes damping off in seedlings, and Fomes pappianus, a stem rot that attacks unhealthy trees. In 1990, Fomes lignosus was observed causing a serious root rot disease in strip plantations containing A. nilotica and other species in Bangladesh. The affected trees died in patches showing wilting symptoms. The leaves of affected trees become brown, dry up and remain on dead branches (Basak, 1999). Various species of Aspergillus, Penicillium, Rhizopus and Geotrichum have also been recorded causing dieback in seedlings of A. nilotica. Plantations using agroforestry systems (see Silviculture section) have proved to be effective in reducing fungal attack.
Insects
According to Brunck (1994), the most important insect is the stem borer Celosterna scabrator [Cerosterna scabrator], which affects young plantations by causing dieback, in India. The most important leaf defoliators are Euproctis lunata and Euproctis subnotata, which occasionally defoliate patches of forest in the Sukkur and Hyderabad circles, India. The most important insects that affect the seeds are two bruchid beetle species in Africa, Bruchidius uberatus and Callosobruchus maculatus, which destroy up to 70% of the seed crop (Ernst et al., 1990; Miller, 1996). Flower thrips, including Megalurothrips distalis, Thrips hawaiiensis and Scirtothrips sp. are among the most important insects attacking flowers of A. nilotica. Heavy infestations of thrips caused weak growth and premature shedding of flowers, resulting in poor fruit set (Kumar et al., 1999). Powder post beetles (Sinoxylon anale and Lyctus africanus) attack the sapwood of felled timber.
Mammals
Overgrazing (particularly on young seedlings) and overcutting (for fuelwood and timber) have been a problem for the sustainability of natural stands and plantations of this species in some parts of its range (Wickens et al., 1995).
Abiotic Factors
Brunck (1994) also gives an estimate of importance for each pest and disease from the African and Indian continents; the most important insect is the stem borer C. scabrator [C. scabrator], which affects young plantations by causing dieback, in India.
Seed germination and seedling survival of A. nilotica and Azadirachta indica were highest with soil solarization in combination with insecticide application in India (Kaushik et al., 2002). Plants previously inoculated with vesicular arbuscular mycorrhizas (VAM) significantly increased survival percentage compared to both Rhizoctonia solani and F. oxysporum in A. nilotica (Kaushik et al., 2000).
List of Pests
Notes on Natural Enemies
Although a wide range of herbivores and pathogens attack living A. nilotica trees, none limit cultivation. Reviews by Browne (1968), Roberts (1969), Mohyuddin (1981), Sheik (1989) and Brunck (1994) give an estimate of the importance of each pest and disease from Africa and India. The most important insect is the stem borer Cerosterna scabrator which affects young plantations in India, causing dieback. The most important leaf defoliators are Euproctis lunata and E. subnotata, which occasionally defoliate patches of forest in the Sukkur and Hyderabad circles, India. The most important fungi are Fusarium oxysporum, which causes damping off in seedlings and Fomes pappianus, a stem rot that attacks unhealthy trees. The most important insects which affect seeds are two bruchid beetle species in Africa, Bruchidius uberatus and Callosobruchus maculatus which can destroy up to 70% of the seed crop (Ernst et al., 1990; Miller, 1996). Powder post beetles (Sinoxylon anale and Lyctus africanus) attack the sapwood of felled timber.
Natural enemies
| Natural enemy | Type | Life stages | Specificity | References | Biological control in | Biological control on |
|---|---|---|---|---|---|---|
| Cerosterna scabrator | Herbivore | Plants|Stems | not specific | |||
| Euproctis lunata | Herbivore | Plants|Leaves | not specific | |||
| Fusarium oxysporum (basal rot) | Pathogen | Plants|Seedlings | not specific | |||
| Fomes pappianus | Pathogen | Plants|Stems | not specific | |||
| Bruchidius uberatus | Herbivore | Plants|Seeds | not specific | |||
| Callosobruchus maculatus (cowpea weevil) | Herbivore | Plants|Seeds | not specific | |||
| Euproctis subnotata | Herbivore | Plants|Leaves | not specific |
Impact Summary
| Category | Impact |
|---|---|
| Animal/plant collections | None |
| Animal/plant products | None |
| Biodiversity (generally) | Negative |
| Crop production | None |
| Environment (generally) | Negative |
| Fisheries / aquaculture | None |
| Forestry production | None |
| Human health | None |
| Livestock production | Negative |
| Native fauna | None |
| Native flora | Negative |
| Rare/protected species | None |
| Tourism | None |
| Trade/international relations | None |
| Transport/travel | None |
Impact
The invasion of grass pasture such as in the Astrebla grassland system of Australia, interferes with cattle and sheep enterprises (Carter, 1998). In Queensland, the spread of the tree has reduced the amount of available pasture. Carter (1998) estimates 50% pasture reduction at 25-30% tree canopy cover. However, it should be noted that the spread of the tree in Australia was initially promoted by livestock managers because its use as a browse tree provided a protein supplement (Carter, 1998). Carter (1998) attributes land degradation of savanna grazing systems to be a direct consequence of combining the use of A. nilotica as a browse species with inappropriate stocking levels. When dense thickets of the tree arise, stock herding is made more difficult and animals may have reduced access to water (Anon., 2001). Drainage systems also become more expensive to operate because the trees use some of the water (Anon., 2001).
Impact: Economic
The invasion of grass pasture by A. nilotica such as in the Astrebla grassland system of Australia, interferes with cattle and sheep enterprises (Carter, 1998). In Queensland, the spread of the tree has reduced the amount of available pasture. Carter (1998) estimates 50% pasture reduction at 25-30% tree canopy cover. However, it should be noted that the spread of A. nilotica in Australia was initially promoted by livestock managers because its use as a browse tree provided a protein supplement (Carter, 1998). Carter (1998) attributes land degradation of savanna grazing systems to be a direct consequence of combining the use of A. nilotica as a browse species with inappropriate stocking levels. When dense thickets of the species arise, stock herding is made more difficult and animals may have reduced access to water (Anon., 2001). Drainage systems also become more expensive to operate because the trees use some of the water (Anon., 2001).
Impact: Environmental
Acacia nilotica infestations accelerate erosion processes (Anon., 2001). According to Weber (2003), A.nilotica subsp. indica has transformed large areas (over 6.6 million ha) of Australian grassland into scrub. This species out-competes native grasses (Anon., 2001). In Indonesia, the spread of A. nilotica in the Baluran National Park has limited animal movements and reduced the amount of grazing available for herbivores (Anon., 2002). The nitrogen-fixing characteristic of this species is also likely to lead to changed patterns of nutrient cycling. In the Caribbean, Australia, Indonesia and New Caledonia, it is spreading vigorously in many locations where it grows as a weed and as an invasive species.
Impact: Social
The long thorns of A. nilotica can be a nuisance for farmers unused to their presence.
Risk and Impact Factors
Invasiveness
Invasive in its native range
Proved invasive outside its native range
Highly adaptable to different environments
Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
Highly mobile locally
Has high reproductive potential
Has propagules that can remain viable for more than one year
Impact outcomes
Damaged ecosystem services
Ecosystem change/ habitat alteration
Negatively impacts agriculture
Negatively impacts tourism
Reduced amenity values
Reduced native biodiversity
Impact mechanisms
Competition - monopolizing resources
Produces spines, thorns or burrs
Likelihood of entry/control
Highly likely to be transported internationally deliberately
Difficult/costly to control
Uses
Acacia nilotica is popular as an agroforestry tree, either sown in lines 5 m apart in agricultural fields, or on field crop boundaries. As a fodder tree, it is utilized in many different silvopastoral systems and its sweet-smelling pods are particularly sought out by animals. It is extensively used in land rehabilitation, being planted on saline and alkaline soils. It will also grow when irrigated with tannery effluent, or saline water and effectively colonizes waste heaps from coal mines. The tree is popular as a shelterbelt and there is interest in A. nilotica subsp. cupressiformis as a windbreak surrounding fields because its narrow crown form produces less shade than other taxa. It is also a popular ornamental tree and is frequently planted in India as an avenue tree.
Since the time of the Pharaohs, large timber trees have been exploited from the riverine forests of the Nile in Sudan and Egypt. At present, forests in the Sudan are managed on a 20- to 30-year rotation, producing termite-resistant timber especially suitable for railway sleepers. In India and Pakistan, the riverine plantations are managed on 15- to 20-year rotations for fuelwood and timber such as mine props. The strong and durable wood is nearly twice as hard as teak and is very shock resistant. It is used in construction in tool handles and carts. Wood properties are reviewed by Rao and Purkayastha (1972), Goldsmith and Carter (1981), Tewari and Rajput (1987) and Troup and Joshi (1983) and its rayon pulp and paper pulp properties by the Food and Agriculture Organization, Forestry Department (1980) and Guha et al. (1974). The dark brown hardwood has a high calorific value of 4950 kcal/kg, making excellent fuelwood and high-quality charcoal (National Academy of Sciences, USA, 1980).
The pods and leaves have high levels of crude (12.4%) and digestible protein (8%) and energy (7.2 MJ) and are rich in minerals (Houerou, 1980). Pods are used as a supplement to poultry rations in India. Dried pods are relished and particularly sought out by animals grazing on rangelands as the pods mature towards the end of the dry season. In India, branches are commonly lopped for fodder. Pods are best fed as a supplement.
A by-product from felling is the bark, which has high levels of tannin (12-20%) used for tanning leathers in India and the pods of A. nilotica subsp. nilotica have been used for over 6000 years in Egypt for tanning. A. nilotica subsp. adstringens is used both for tanning and as a dye in Nigeria.
The gum of A. nilotica was originally called gum arabic and has been collected from the Nile forests since the time of the Pharaohs, for use in paints and medicines. It has some properties similar to those of true gum arabic (from Acacia senegal) and is frequently used in calico printing, dyeing, sizing material for silk and cotton and in paper manufacture in India. In Mumbai, India, it is marketed as Amravati gum.
The tannin content contributes to the many medicinal uses of A. nilotica, acting as a powerful astringent. It has also been found to be a powerful molluscicide and algicide and the fruits, when added to ponds in Sudan, killed snail species which carry schistosomiasis, without affecting fish (Ayoub, 1982). The tree is a good host plant for growing lac (shellac) in Sind, Pakistan. An extract of the root is a potential inhibitor of Tobacco mosaic virus. In eastern Java, sprouted seeds are eaten as vegetables and well-roasted seeds are mixed with coffee (Coffea) (Lemmens and Wulijarni-Soetjipto, 1991). There are many other reported uses (Fagg and Greaves, 1990).
Uses List
Environmental > Agroforestry
Environmental > Boundary, barrier or support
Environmental > Revegetation
Environmental > Shade and shelter
Environmental > Windbreak
Materials > Dye/tanning
Materials > Fibre
Materials > Gum/resin
Materials > Miscellaneous materials
Materials > Wood/timber
Medicinal, pharmaceutical > Source of medicine/pharmaceutical
Medicinal, pharmaceutical > Traditional/folklore
Fuels > Charcoal
Fuels > Fuelwood
Animal feed, fodder, forage > Fodder/animal feed
Animal feed, fodder, forage > Invertebrate food for lac/wax insects
Wood Products
Roundwood > Building poles
Roundwood > Pit props
Roundwood > Roundwood structures
Roundwood > Stakes
Sawn or hewn building timbers > Beams
Sawn or hewn building timbers > Carpentry/joinery (exterior/interior)
Sawn or hewn building timbers > Engineering structures
Sawn or hewn building timbers > Exterior fittings
Sawn or hewn building timbers > Fences
Sawn or hewn building timbers > Flooring
Sawn or hewn building timbers > For heavy construction
Sawn or hewn building timbers > For light construction
Woodware > Industrial and domestic woodware
Woodware > Tool handles
Woodware > Wood carvings
Other > Charcoal
Other > Railway sleepers
Other > Textiles
Prevention and Control
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Control
Cultural Control
Acacia nilotica is resistant to grazing (Weber, 2003). However, spread is slower in sheep-only livestock enterprises and intense sheep grazing may counteract A. nilotica in the seedling stages (Carter, 1998). Carter (1998) considered that investigation of appropriate livestock combinations for use in grassland-A. nilotica farming systems would be worthwhile. Appropriate management of livestock densities should enhance the ability of perennial grasses to outcompete acacia seedlings while overstocking promotes invasion (Anon., 2001). Preventing sheep and cattle grazing in the vicinity of mature pods restricts potential dispersal through the livestock gut and allows insects to predate the seeds (Anon., 2001). Fences may be erected to achieve this, or the time at which animals roam the grazing area may be restricted to avoid periods when ripe seed pods are available (Anon., 2001). Cattle and sheep should be quarantined if they are moved between infested and non-infested areas to allow seeds to pass through the gut (up to 6 days) (Carter and Cowan, 1993). The replacement of bore drain irrigation with piped water to restrict tree access to favourable reproductive sites is recommended (Anon., 2001). Kriticos et al. (1999b) cites the use of fire to control acacia seedlings but since this requires early removal of stock, the relative economic benefits of controlling the invasive trees must be weighed against the temporary loss of livestock grazing.
Physical/Mechanical Control
According to Weber (2003), mechanical methods are used after the application of chemicals. A. nilotica has the capacity to resprout after damage (Weber, 2003) and though it does not produce root suckers regularly, there are some records of suckering in addition to coppicing ability (Sheik, 1989). Detailed information on mechanical practices in Australia is available (Anon., 2001). These include the use of tractors to grub up medium density infestations of trees with diameter up to 15 cm, prior to pod ripening; pushing the trees down during a drought or outside the period of ripe seed availability; stick raking during a drought or outside the period of ripe seed availability and double chain pulling for high densities during prolonged drought.
Biological Control
Although seed predators from native range countries constitute potential biological control agents, Carter (1998) reports that benefits are liable to be limited by stock management practices, since seeds may be eaten and redistributed by grazing animals before insects such as the bruchid beetles Caryedon serratus and Bruchidius sahlbergi gain access. Many of the insect species that feed on native Australian acacias are able to feed on A. nilotica, weakening plants and contributing to enhanced mortality rates (Anon., 2001). B. sahlbergi was introduced to Australia from Pakistan in 1979 and seed predation rates are noted to vary in association with ripe seed pod availability (Anon., 2001). Further releases to Australia from Kenya have included the beetle Homichloda barkeri and the geometrid caterpillars Chiasmia inconspicua and C. assimilis and there are ongoing investigations for an effective agent (Anon., 2001).
Chemical Control
According to Weber (2003), the herbicides 2,4-D and triclopyr are applied by various methods including basal bark application, pasting onto cut stumps, direct injection into the stems and spraying onto foliage. Comprehensive information on the use of chemicals to counteract A. nilotica in Australia is available (Anon., 2001). The range of approaches described includes basal bark spraying during periods of good soil moisture and active plant growth, pasting on cut stumps (at any time of year), application to the soil prior to rainfall (with herbicides being taken up through the plant roots), foliar spraying of plants less than 2 m tall, spraying by helicopter and treatment of empty drainage channels. The latter method cannot be used when the water supplies domestic systems or where there are desired trees.
Integrated Control
Anon. (2001) advocates a strategic approach to the control of A. nilotica spread, which takes account of the distribution of the species in relation to water courses and grazing paddocks, recommending priority areas for control, in particular those trees with good water supply and thus highest potential reproduction. There have been recent attempts to model spread in relation to biological and population characteristics, environmental and management factors and climate change, as a management tool (Kriticos et al., 1999a, b). Kriticos et al. (1999b) cites the long-time lag between recruitment and measurable production impact as the main factor preventing the development of a management regime that responds to a critical economic impact threshold. It is interesting to note that, although the plant was first designated a noxious weed in Australia in 1957, land managers were initially reluctant to control it and continued to actively plant it because of its use as a shade and fodder tree (Carter, 1998).
Silviculture Characteristics
Acacia nilotica is a pioneer species (light-demanding), that colonizes a wide range of dry sites, and seed dispersal is via animals. It regenerates well from seed, providing that grazing pressure is low. It will also form riverine woodlands, where it develops into large timber trees.
It is a fast-growing species, and is grown at close spacing for fuelwood which is later thinned for timber production, or at wider spacings for agroforestry farming systems. A. nilotica subsp. indica is pollarded for fodder in India. It is also popular as an avenue and hedge plant, and is broadcast on degraded saline and/or alkaline soils, growing on soils with up to pH 9. Depending on the subspecies, it will tolerate both drought and flooded conditions for several months.
Silviculture Characteristics
Tolerates > drought
Tolerates > waterlogging
Ability to > fix nitrogen
Ability to > regenerate rapidly
Ability to > coppice
Ability to > pollard
Silviculture Practice
Acacia nilotica is a pioneer species easily regenerated from seed. The nutritious indehiscent pods have evolved for animal dispersal. A mature tree can produce 2000-3000 pods in a good fruiting season, each with usually between 8 and 16 seeds, yielding 5000 to 16,000 seed/kg depending on the subspecies. The species will produce pods in abundance after age 5 to 7 years.
Hard coated seeds can be extracted by pounding the pods followed by winnowing and cleaning, or collecting from animal pens after the pods have been eaten (Sheikh, 1989). They store well under cool dry conditions and then require pretreatment.
The easiest method of pretreatment is to pour boiling water over the seeds and allowing it to cool. Acid scarification (for 60 to 120 minutes, depending on the provenance or the age of the seed) is also effective. Mechanical scarification works best for small seed lots (nicking the seed coat opposite the micropyle end with nail clippers or sandpaper). On a large scale, seed can also be fermented in cow-dung or manure heaps for 48 hours, the heaps kept constantly moist until the seeds imbibe well and swell, when they will be ready to be sown in the nursery.
Innoculating the seed with improved rhizobia strains can increase early growth (Luna, 1996), and salt-tolerant Rhizobium isolates have also been tested which can nodulate and fix nitrogen in saline soils (Lal and Khanna, 1994).
There are a number of reports of vegetative propagation (Garg et al., 1996; Mathur and Chandra, 1983), although regeneration by seed is the preferred and easier option.
Plants can be direct sown (most common because of its long tap root development), or planted into long poly tubes (20 x 7 cm) for four months in the nursery and then planted in the field when the height is around 25 to 30 cm. A spacing of 3 x 3 m between trees is common. Establishment varies considerably depending on the sites, and is reviewed in Troup and Joshi (1983), Sheikh (1989) and Luna (1996). Seedlings are shade intolerant and require systematic weeding for the first 2-3 years. For fuelwood and timber in irrigated plantations in the Sind and Punjab, between 10 and 15 seeds are spot sown on a 2 x 3 m spacing on the berms of trenches. They are thinned after 3-4 months to 3-4 seedlings, with further thinnings at intervals of 5 years, rotations usually taking 20 - 25 years.
One popular and economical direct sowing technique has been an agroforestry method developed in Maharashtra state (India), where lines of A. nilotica and Azadirachta indica are sown at spacings of about 5 m apart, and agricultural crops are raised between the rows of trees. When planted for the production of tannin and gum, A. nilotica should have sufficient space (4 x 4 m) so that each tree receives enough light. Thinning is necessary to maintain maximum growth of the stand, as is systematic weeding.
In Pakistan, A. nilotica is grown on short rotations in impounded overflow from irrigation canals off the Indus barrages, known as 'hurries' (D. Hocking, personal communication).
The tree is reported to be a good host for the lac insect in Gujarat and adjoining areas of Rajasthan (India), although in other areas of India it has been disappointing (Troup and Joshi, 1983). It is also a good host for sandalwood (Padmanabha et al., 1988).
Silviculture Practice
Seed storage > orthodox
Vegetative propagation by > cuttings
Vegetative propagation by > tissue culture
Stand establishment using > natural regeneration
Stand establishment using > direct sowing
Stand establishment using > planting stock
Management
Estimates of productivity of plantations and natural stands vary considerably with site conditions, reviewed by Sheikh (1989), Luna (1996), Troup and Joshi (1983) and Fagg and Greaves (1990). Growth rate is relatively fast, with figures for plantations on average sites of 3 to 5 cubic metres per hectare per year over a 15-20 year rotation (Pandey, 1987), and maximum figures of from 3 to 9 cubic metres per hectare per year between ages 10 and 15 years in Rajasthan and Uttar Pradesh (Singh, 1982). In the Sind riverine forests a maximum mean annual increment of 13 cubic metres per hectare at age 20 years, and 10.5 cubic metres per hectare at age 30 years, on Quality 1 sites (Sheikh, 1989) has been recorded.
At 600 plants per hectare, 12 tonnes of bark was produced in a 15-year rotation (Lemmens and Wulijarni-Soetjipto, 1991). Pods are another useful product from the plantations, with yields of 8-10 tonnes of pods/ha/year (Singh, 1982).
Genetic Resources and Breeding
Acacia nilotica shows a great deal of morphological variation, nine subspecies being recognized (Brenan, 1983), indicative of high levels of genetic variation. The species is insect pollinated and outcrossing, and the taxa form a polyploid complex: most are tetraploids (2n=4x=52); but higher numbers have been found in A. nilotica subsp. nilotica (2n =104) and A. nilotica subsp. tomentosa (2n=208) (Nongonierma, 1976).
A number of early trials were based on relatively few collections. Plant material was collected and trialled in a FAO/IBPGR project for arid zone species (Armitage et al., 1980), but again sampling was from relatively few sites. More recently, rangewide collections in Africa have been undertaken by the Oxford Forestry Institute (OFI) and members of the African Acacia trials network (comprising OFI, CIRAD-Forêt, and DFSC), co-ordinated by the FAO, and seed is available for trials (Fagg et al., 1997).
There have been a number of international provenance trials planted but these have yet to be evaluated. In India, large provenance trials of A. nilotica subsp. indica have recently been planted, and data on germination, seedling growth and nitrogen fixation is given in Krishan and Toky (1996) and Toky et al. (1995).
The mating system of A. nilotica subsp. leiocarpa was investigated by A. K. Mandal. By scoring three enzyme systems in starch-gel electrophoresis, isozyme banding patterns within families suggested that the species is autotetraploid, displaying tetrasomic inheritance. The best level of outcrossing was tm=0.384, highly significantly less than one. These suggested that the species is self compatible, and approximately 60% of seeds are set through self pollination (Mandal et al., 1994). Controlled pollinations are needed to estimate the degree of compatibility, and assessing the factors controlling the extent of outcrossing in this species, otherwise heritability will be overestimated from open pollinated progeny trials.
Disadvantages
The pioneer characteristics of A. nilotica (competing for space, light, water and nutrients, often on overgrazed lands) result in an invasive propensity and the formation of thorny thickets (Wells et al., 1986), and it has become a major weed in Australia and Java (Carter, 1994). The long thorns can be a nuisance for farmers not used to them. A. nilotica should not be introduced into humid and subhumid areas, or into dry areas where there are adequate supplies of grazing and fuelwood.
Links to Websites
| Name | URL | Comment |
|---|---|---|
| GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway | https://doi.org/10.5061/dryad.m93f6 | Data source for updated system data added to species habitat list. |
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References
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