The dearth of effective steps to arrest the rampant growth of invasive plants, especially Senna spectabilis, in the forest areas of the Nilgiri Biosphere Reserve (NBR), including the Wayanad Wildlife Sanctuary, is a matter of serious concern to the conservation of wildlife habitats of the Western Ghats.
A recent study, organised by Ferns, a nature conservation society, in association with the Kerala Forest Department, revealed that the invasive species has now spread through the most iconic wildlife habitats of the Western Ghats, destroying habitats of elephants, deer, gaur and tigers by pushing out native flora.
The allelopathic traits of the species prevent other plants from growing under it. “It is a form of chemical warfare where the shed leaves decompose and change the chemical composition of the soil, rendering it unsuitable for the growth of other plant species,” P.A. Vinayan, president, Ferns, who led the study, said.
This drastically affects primary productivity at the ground level. The forest floor is almost bare under the invasive species. Grasses and herbs get completely wiped out and herbivores are deprived of their forage. “The carrying capacity of forests to feed wildlife is drastically declining under the invasion, which accelerates man-animal conflict further,” Mr. Vinayan said.
The invasive species found its way to Wayanad in the 1980s, when the seedlings of the plant were first raised in the nurseries of the social forestry wing, and planted as avenue trees. It was noticed regenerating profusely about 25 years after its introduction in Wayanad. Over the period, it got established in the Bandipur and Nagarhole Tiger Reserves of Karnataka, and the Mudumalai and Sathyamangalam Tiger Reserves in Tamil Nadu as well, he said.
The Forest Departments of Karnataka and Kerala realised that the tree is a threat to native biodiversity nearly 10 years ago and initiated actions to contain its spread. The study found around 23% of the area of Wayanad Wildlife Sanctuary is infested by Senna spectabilis. The study says 1,305 trees were found in one hectare in the most affected areas of the sanctuary. The species are spreading at almost the same rate in the adjacent Tiger Reserves.
The Kerala Forest Department attempted to remove the trees by uprooting, girdling, cutting, chopping the tree branches, and even testing the application of chemicals. However, all the efforts were in vain. Instead, multiple coppice shoots started growing from each cut tree stump.
The situation is similar in the Karnataka and Tamil Nadu.
Senna eradication is a major component of the sanctuary’s forest management plan but it’s yet to make any remarkable change in the forest, Wayanad Wildlife Sanctuary Warden S. Narendra Babu said. A long-term joint drive by the authorities of the adjoining Tiger Reserves in Karnataka and Tamil Nadu States is the only possible solution to eliminate the threat, he said.
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