Grassland invaders stifle Assam’s island-like national park

UPSC Relevance:

UPSC has been asking questions on vegetation and plant species and their peculiar features.

PYQ:  2021

Which one of the following is used in preparing a natural mosquito repellent?

(a) Congress grass

(b) Elephant grass

(c) Lemongrass

(d) Nut grass

Study on Ecosystem Changes in Dibru-Saikhowa National Park:

A study titled “Grasslands in Flux” analyzed land use and land cover (LULC) changes in Dibru-Saikhowa National Park (DSNP) from 1999 to 2024. The findings were published in the peer-reviewed journal Earth.

Key Discovery – The study identified that two native flowering tree species, Bombax ceiba (Simalu – in Assamese) and Lagerstroemia speciosa (Ajar – in Assamese ), are acting as “invaders” alongside few well-known invasive alien species like shrub Chromolaena odorata , herb Parthenium hysterophorus and climber Mikania Micrantha.

• An invasive alien species refers to an alien species whose introduction and/or spread threatens the biological diversity of the region/habitat .

Contributing Factors to Ecosystem Changes- The primary reasons for the changes in DSNP’s ecosystem are:

• The spread of native and invasive plant species via humans and water.
• Recurring floods from the Brahmaputra River.
• Increasing human pressure from forest villages within the park’s boundaries.

Impact of Plant Invaders –  They are altering the landscape, causing a decline in the park’s dominant grasslands.

Observed Land Cover Changes (1999-2024)

• In 2000, grasslands made up 28.78% of the park.
• By 2013, shrubland became the most prominent class, and degraded forest areas expanded.
• In 2024, degraded forest further increased to 23.47%, indicating a consistent decline in grassland and semi-evergreen forest areas.
• This indicates human induced ecological succession.
  • Ecological succession is the gradual process of change in the species structure of an ecological community over time. It is a predictable and continuous process where one community of species is gradually replaced by another, until a stable ecosystem, known as a climax community, is established. However, anthropogenic factors may either pace up or slow down these natural processes.

Threat to Biodiversity – The shift in the landscape’s structure poses a significant threat to grassland-dependent fauna, many of which are already globally threatened. Species at risk include the Bengal florican [Houbaropsis benga-lensis], Hog deer [Axis porcinus], and swamp grass babbler [Prinia cine-rascens]. The park is also home to about 200 feral horses.

• A feral horse is a free-roaming horse of domesticated stock. Unlike a wild animal that has never been domesticated (like a tiger or a zebra), a feral horse’s ancestors were at one point domesticated by humans. The only truly wild horse species remaining in the world is the Przewalski’s horse (also known as the takhi) of Mongolia.
• In India, feral horses are primarily found in the Dibru-Saikhowa National Park in Assam. There is also a small population in the Point Calimere Wildlife and Bird Sanctuary in Tamil Nadu.
• The exact origin of the feral horses in Dibru-Saikhowa is debated, but the most widely accepted theory is that they are descendants of military horses abandoned by British and American troops after World War II.

Study Recommendations for Recovery – The study suggests a comprehensive grassland recovery project that includes:

Implementing LULC-based management to protect habitats and enhance the survival of native plants and animals.

• Controlling invasive species
• Improving surveillance
• Increasing staffing
• Relocating forest villages to reduce human impact

Dibru-Saikhowa National Park:

• Location and Status – Located in the Dibrugarh and Tinsukia districts, it’s a national park as well as a UNESCO Biosphere Reserve. It was declared a national park in 1999, two years after it received its biosphere reserve status. It’s also an Important Bird Area (IBA).
• Unique Habitat – It’s an island-like formation between the Brahmaputra and Lohit rivers to the north and the Dibru River to the south. This location makes it a riverine ecosystem prone to recurring floods, which have a significant impact on its landscape.
  • It’s a mix of moist mixed semi-evergreen forests, tropical moist deciduous forests, and grasslands. It is considered the largest Salix swamp forest in northeastern India.

• Feral Horses – Dibru-Saikhowa is the only habitat for feral horses in India. 
• Key Fauna –  The park is a haven for many rare and endangered species. It was originally established to protect the white-winged wood duck. It is also home to the Gangetic river dolphin, hoolock gibbon, Bengal tiger, and numerous other mammals, reptiles, and fish. 

Read more about invasive species : Water Hyacinth – The terror of Bengal