Context

The Forest and Wildlife Department is planning to adopt 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.

About

The need:

• The spread of invasive plants, especially Senna spectabilis, is posing a major threat to the forest areas of the reserve, owing to its quick growth and coppicing character.
• Invading larger areas: A recent study of the Ferns Nature Conservation Society recorded the presence of the plant in 78.91 sq km area of the sanctuary. The tree species was found in nearly 10 sq km area of the 344.44 sq km sanctuary around five years ago. Now, it had invaded to more than 50 sq km of the sanctuary.
• Emerging as a trap for open lands: Due to mass flowering and drying of bamboo species in Wayanad, lots of open spaces were created which had been occupied by Senna spectabilis. The vayal ecosystem (marshy land) of the forest area now has this plant in large numbers.
• Threat to tiger reserves: With the adjacent tiger reserves (Bandipur and Nagarhole tiger reserves in Karnataka and the Mudumalai tiger reserve in Tamil Nadu) also under threat.

What are the Invasive alien species?

• Invasive alien species are plants, animals, pathogens and other organisms that are non-native to an ecosystem, and which may cause economic or environmental harm or adversely affect human health.
• In particular, they impact adversely upon biodiversity, including decline or elimination of native species - through competition, predation, or transmission of pathogens - and the disruption of local ecosystems and ecosystem functions.
• In 2016, the Zoological Survey of India (ZSI) has for the first time compiled a list of 157 alien invasive animal species.
• Out of the total species, 99 are found in the marine ecosystem, while 58 are found on land and in freshwater habitat.
• The species found on land and in freshwater comprise of 19 fish species, 31 species of anthropods, 3 of molluscs and birds, 2 of mammals and 1 of reptile.
• Among 99 alien invasive marine species, genus Ascidia accounts for maximum number of species (31), followed by Arthropods (26), Annelids (16), Cnidarian (11), Bryzoans (6), Molluscs (5), Ctenophora (3), and Entoprocta (1).
• Some important species include: African apple snail (Achatina fulica), Papaya Mealy Bug (Paracoccus marginatus), Cotton Mealy Bug (Phenacoccus solenopsis), Amazon sailfin catfish (Pterygoplichthys pardalis) and others.

Senna Spectabilis:

• Senna spectabilis is a medium to large tree from tropical America, listed in the Global Compendium of Weeds as an ‘environmental weed’, ‘garden thug’, and ‘naturalised weed’.
• The species is extremely fast-growing, flowers and sets seed profusely, and re-sprouts readily when cut.
• An adult tree grows up to 15 to 20 metres in a short period of time and every year distributes thousands of seeds after gregarious flowering.
• The thick foliage arrests the growth of other indigenous tree and grass species and causes food shortage for the wildlife population, especially herbivores.

Why alien plants are so dangerous?

• Greatest threat to biodiversity: Invasive alien species, introduced and/or spread outside their natural habitats, have affected native biodiversity in almost every ecosystem type on earth and are one of the greatest threats to biodiversity.
• Contributor to animal extinction: Since the 17th century, invasive alien species have contributed to nearly 40% of all animal extinctions for which the cause is known (CBD, 2006).
• Problem for ecology and economy: The problem continues to grow at great socio-economic, health and ecological cost around the world. Invasive alien species exacerbate poverty and threaten development through their impact on agriculture, forestry, fisheries and natural systems, which are an important basis of peoples’ livelihoods in developing countries.
• This damage is aggravated by climate change, pollution, habitat loss and human-induced disturbance.