WHEN one thinks of invasions, names of kings and rulers from history come to mind. Names of plants like Prosopis juliflora, Lantana camara and Parthenium hysterophorus are never linked to invasions. However, while invading kings are now just a part of history, invasive plants are still there, and are a huge threat to the local flora, fauna and agriculture. Invasive plants are those which?spread to regions?other than their native and thrive to the extent of becoming a threat to?local species.
Prosopis juliflora (P juliflora), an exotic tree, is one of the top invaders in India. A native of South and Central America, it was introduced in India to meet the fuel?wood requirement of the rural poor and to restore degraded lands. A recent study by S Chandrasekaran, associate professor?at the department of plant sciences, school of biological sciences, Madurai Kamaraj University, and his colleagues?has shown?that apart from threatening?local plants, with whom it competes for resources, this tree is also affecting the nesting success of birds. The study was published in the journal Current Science on 10 March.
The team carried out its studies at the Vettangudi Bird Sanctuary in Tamil Nadu. The vegetation in the sanctuary is dominated by Prosopis and Acacia nilotica, a native tree variety. The forest department conducts an annual bird census in the sanctuary where it involves scholars from the local university. Chandrasekaran and his team were part of the census conducted by the forest department in 2011?during which?locations of nests in Prosopis and Acacia were studied. The number of nests per tree, eggs per nest, fallen eggs and chicks, and population at the fledgling stage were recorded in the census.
The results showed that in Acacia, nests were located at nodes with more than two branches and were distributed evenly on the trees, whereas in Prosopis, they were located not just at nodes?
but?all?over?the?branches.?The number of nests on Prosopis plants was significantly higher than it was in the Acacia. No significant difference in eggs per nest was noticed between the plants but the number of fallen eggs and chicks on the ground was much higher for Prosopis. ‘Our preliminary observation reveals that during nest construction and reconstruction process, the wetland birds preferred new twigs of Acacia than those of Prosopis,’?says Chandrasekaran. As is evident, the invasive species draws birds into unfamiliar zones?that are inadequate for its nesting requirements and this results in smaller population of the bird.
By arrangement with Down to Earth magazine