Forests

A weed and a tale

In the forests of Kanyakumari, an invasive species has been proliferating since the 1960s. It is time to remove it altogether

 
By V Sundararaju
Last Updated: Wednesday 16 May 2018
The well-grown trees covered by the climber are seen in this panoramic photo       Credit: V Sundararaju
The well-grown trees covered by the climber are seen in this panoramic photo       Credit: V Sundararaju The well-grown trees covered by the climber are seen in this panoramic photo Credit: V Sundararaju

In the 1960s, ethnic strife in the island nation of Sri Lanka, which ended in 2009, was rife. It caused many Sri Lankan Tamils to cross the Palk Strait and enter Tamil Nadu, seeking refuge. India’s then-Prime Minister, Lal Bahadur Shastri and the then-Lankan President, Sirimavo Bandaranaike signed an agreement to accommodate the refugees. As most of them had been working in plantations like tea and rubber in Sri Lanka, it was decided to create similar plantations in Tamil Nadu to employ and rehabilitate them. Accordingly, forests in the districts of Kanyakumari and Nilgiris were chosen and converted into rubber and tea plantations.

The Kanyakumari Forest Division leased about 5,000 hectares of reserve forests to the Arasu Rubber Corporation (ARC) Limited for raising rubber plantations to rehabilitate Tamil refugees from Sri Lanka. Initially, when rubber was raised, Pueraria javanica was introduced as a “cover crop” to prevent soil erosion and for enrichment of the soil. This species is native to Thailand. It is a very popular cover crop in coffee, oil palm, citrus and rubber plantations.

Subsequently, the cover crop was changed. During the 1980s, Mucuna bracteata, a creeping vine that belongs to the legume family, was introduced as cover crop in place of Pueraria javanica. Mucuna bracteata originates in the forests of Tripura. It is used as a cover crop in rubber (India and Malaysia) as well as palm oil plantations (Malaysia).

Mucuna bracteata has several advantages. The creeping crop grows about 10-15 cm/day in rubber and palm oil plantations. It mainly protects raked up soil, prevents erosion, enriches organic matter and helps in retaining moisture. It minimises losses of nutrients due to leaching and reduces competition from noxious weeds. As a rule, leguminous plants are selected as cover crops as they are able to fix nitrogen and make it available to the main crop. Mucuna bracteata does not dry during hot spells. It also grows under the shade. It is non-palatable to cattle due to high levels of phenolic compounds and thus protects crops from cattle and other wild animals. Moreover, it is drought- resistant and poses less fire hazards during dry weather.

Unfortunately, Mucuna bracteata is a deep-rooted and rapidly-growing plant species. In the ARC plantations, the growth of this species became astonishingly vigorous in due course of time, and has now become a menace in the adjoining forest areas.

Since it is a fast-growing, creeping and aggressively climbing perennial vine, it can choke, smother and dwarf native trees by its gregarious growth and climbing behaviour. It has covered the ground completely, climbed upon the well-grown trees and suppressed them completely. Because of the suppression by the weed, the photosynthetic activity has completely stopped. As a result, the trees are gradually facing death.

The natural forest adjoining the ARC’s plantations needs revitalisation. Moreover, it is rich elephant habitat. Therefore, it is the need of the hour to remove this weed completely from the ARC areas contiguous to the forest as this poses a serious threat to the wildlife habitat which has been declared as a Wildlife Sanctuary. In the past, attempts have been made with machinery like JCBs. However, the weed could not be uprooted completely. Even if a small bit of its root is left in the soil, it will grow vigorously and cover the whole area within no time. It is very difficult to remove the weed once it is established.

As Mucuna bracteata has become a major threat, it is high time that the Forest Department and the ARC jointly embark on a programme to eliminate the invasive species for better management of forests. Legislators, foresters, scientists and environmentalists should come together for enacting a strict legislation to prevent the use of this harmful weed in plantations nearer to natural forests.  

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