Post-floods, Vazhachal’s winged species hit a low

Aathira Perinchery, Kochi
The Hindu, February 22, 2019

The results of a two-day survey in Vazhachal’s riverine stretches, including areas affected by last year’s floods, seem disquieting. It records a ‘low’ abundance of some insect taxa – butterflies and odonates (damsel and dragonflies) – as well as birds, especially along the Chalakudy river.
But with no similar surveys for comparison, do these results portray the actual impacts of the flood?
On February 9 and 10, volunteers – both amateurs and experts in species identification – from across the State recorded bird, butterfly and odonate species diversity and counted their numbers in 20 locations along the Chalakudy river and its streams. This revealed 196 bird species (including the great hornbill), 131 butterfly and 51 odonate species.
Though this shows “high” species diversity, the counts of all these taxa were lesser in flood-affected areas such as the Chalakudy river and higher in smaller streams not affected by the flood, claimed K.H. Amitha Bachan, an assistant professor, who supervised the survey, which was supported by the Kerala State Biodiversity Board and conducted by the Vazhachal Forest Department, the Western Ghats Hornbill Foundation and the Botany Research Department of MES Asmabi College, Kodungalloor.
“The flood damaged about 70% of the riverbank,” he said. “Areas immediately downstream of dams were most affected.”

Tell-tale changes

However, volunteers noted only tell-tale changes such as fallen trees and sand deposits which may not sufficiently capture the changes in the habitat. There is also no similar survey of the area, as well as its birds and odonates – especially abundances – before the flood to make comparisons.
But comparisons can be made, insisted Mr. Bachan, adding that small islands in the river disappeared due to the flood, as did existing mudbanks and sandbars. While new sandbanks appeared in some areas, the depths of pools in others decreased due to the silt deposition. Such alteration and loss of habitat could have caused the lower numbers of odonates, which are very dependent on specific aquatic microhabitats for survival, he said.
The flood would indeed have affected the habitat and its denizens, but without previous data for comparison it would not be useful, commented a scientist independent of the survey.
Rejuvenating ancient riparian forests would not be easy, but a project to initiate a tree nursery and plant riparian saplings in appropriate areas during the monsoon has been mooted, said Divisional Forest Officer of Vazhachal, S.V. Vinod.