January 27, 2013

Acacia Arabica (Nilotica)

A tree which I commonly call ‘thorny bush,’ is very prevalent all around Arunachala. The indigenous variety of Acacia in these parts is, ‘Acacia Arabica—Karuvelamaram’ which is another name for the ‘Acacia Nilotica’. 

This tree which is popularly known as ‘Babool’ or ‘Babul’ in other parts of the country, is a small to medium tree, 7 to 13 metres tall, with a stem diameter of 20 to 30 centimetres. Its crown is low and spreads almost symmetrically. The bark is very dark brown to black with deep regular vertical grooves in older specimens. The thorns are almost straight, paired at the nodes of the stem and usually pointing slightly backwards. 

‘Acacia Nilotica’ is a slow-growing species but is moderately long-lived. The species will tolerate only light frost, but is extremely resistant to drought and heat. It is also tolerant of saline soil. Its particularly noted for its vigorous growth in seasonally flooded environments. This species can withstand extremely dry environments and can also endure floods. It thrives under irrigation however it is susceptible to a wide range of pests and diseases in native ranges.

‘Acacia Nilotica’ is multipurpose: it provides timber, fuel, shade, food, fodder, honey, dye, gum, fences as well as various environmental services including soil reclamation for degraded and eroded areas and barrier to desertification, soil fertilization, protection against fire and wind and a haven for biodiversity and ornament. It is widely used in ethno medicine. However it is considered a weed in some countries. This tree makes a good protective hedge because of its thorns. The tree's wood is "very durable if water-seasoned" and is used in the manufacture of tools and boats. Holosericea’ (see below) is here in India. 

‘Acacia Nilotica’ has a wealth of medicinal uses. It is used for stomach upset and pain, the bark is chewed to protect against scurvy, an infusion is taken for dysentery and diarrhoea. It has also been used to eliminate stomach worms, as an antiseptic for open wounds and as an expectorant for treating coughs. 

'Acacia Nilotica’ propagates by seeds carried in animal droppings or by direct seeding and is protected from severe grazing by the presence of long thorns. The pods are desirable as fodder for cattle, and the leaves, young shoots and young pods are thought to aid milk production. The leaves and fruits can be poisonous if eaten in large quantities. 

A serious limitation of this tree is that it is extremely invasive in exotic habitats. Ironically the ‘Acacia Nilotica’ which is regarded as a weed in Australia is as invasive and as damaging in that country, as their own import the ‘Acacia Holosericea’ (see below) is here in India.

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Below is an extract of a report which recently appeared in local newspapers about the dangers of the invasive import, the ‘Acacia Holosericea.’ 

Normally, environmentalists would give their voice for planting trees and not for cutting them. But an invasive tree species, Acacia holosericea, planted in Tiruvannamalai hill several years ago attract their ire. 

Colonies of these trees stand out among thick vegetation found in the southern slope of the hill as they have silvery phyllodes (flattened leaf stalk that looks like and acts as leaf). Real leaves of these trees are less in numbers and are short lived. Environmental activists, feel that the spread of this tree is detrimental to eco system and indigenous flora. Its is believed that Acacia Holosericea may be good in its native land, Australia, however, it becomes invasive in exotic conditions, like in India. 

It causes several problems. First, it spreads fast and dominate indigenous flora. Given a chance, it would eat into bio resources of the hill to a great extent. Second, phyllode litters strewn on the earth will not decompose easily, would not allow other plants to germinate from underneath and may contribute to easy forest fire. Hence these trees should be removed from forest, before its domination becomes irreversible as in Kerala and some other places. Previously it was grown in large numbers in Auroville but after it proved itself to be an invasive species people started destroying it. 

During seasons, parrots come in large numbers to feed on its seeds which exacerbate the vigorous spread of this tree. The popular opinion of NGOs and Forest officials is that the species of Acacia Holosericea is indeed problematic and can be removed. 

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