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How do soil and habitat affect termites of southern India?

Read time: 4 mins

Photo: HS Sudhira / Research Matters

 

When we hear the word ‘termites’, most of us are reminded of the irksome pests that eat away the wood in our houses, causing irreparable damage and expensive chemical treatments. But did you know that termites also act as indicators of the health of an ecosystem and their nests, also called mounds, contain a host of information about the ecology of the region? Now, a new study by a team of Indian and French researchers from the Indian Institute of Science, Bangalore, has tried to understand factors that influence these termite mounds. With data from 579 termite mounds in Bandipur Tiger Reserve, the team investigated the relationship between the abundance and distribution of termite mounds, and the soil properties and the fragmentation of the natural forests.

There are more than 3000 species of termites in the world; over 400 of them are found in Asia, out of which 26 species are considered as pests in India. Termites are detritivores that eat dead and decaying organic matter. They form an important link in the cycling of nutrients in the forests by breaking down wood and organic residues on the ground, which would otherwise take years to decay by microbes. “In the tropics, litter degradation and soil mixing is mainly performed by termites, especially in dry environments”, says Dr. Pascal Jouquet, who has extensively studied termites in southern Indian forests.

Though there are studies that talk about the ecological role of termites, most of them refer to African termites and this remains understudied in Asia. “In African landscapes, termite mounds are called 'hotspots of fertility' or ‘nutrient patches’ and they increase plant and animal diversity in ecosystems. What about Asia?”, asks Dr. Jouquet, also the lead scientist of this team. What controls their distribution and abundance in ecosystems and how they impact nutrient cycling and soil dynamics at the ecosystem scale are also understudied.

Termite mounds are commonly found in southern Indian forests and are of two types - lenticular and cathedral. Lenticular mounds are largely underground with a large dome like shape, while the cathedral mounds are tower-like structures. The researchers looked at these two mounds present in two dominant soil types – namely, a red soil (ferralsol) and a black soil (vertisol), as well as differences between the mounds found inside the forests and on the highway margins. After studying 432 lenticular and 147 cathedral mounds, they estimated the physical and chemical properties, and the volume of soil, in each of these mounds based on their shape.

The findings showed that lenticular and cathedral mounds were abundant in both habitats (forests and highways margins) and that their densities were not dependent on soil type. However, although less conspicuous than cathedral mounds, this study shows the importance of lenticular mounds in terms of soil bioturbation since with about 13 mounds in a hectare (against 2 for cathedral) the volume of soil stored in lenticular mounds reaches between 27 to 47 m3 per hectare in the red and black soil, respectively. Despite the large quantity of soil, their study finds a low impact of termites on nutrient (Carbon, Nitrogen and Phosphorus) distribution at the ecosystem scale. This discovery upsets the belief that termite mounds are “nutrient hotspots” but suggests an important role of termites on soil erosion at the watershed scale.

In conclusion, though many studies on African termites have claimed that termites are sensitive to destruction of habitat, the results of this study show that this may not be true for termites in India. The researchers did not see any difference in termite abundances in both habitats and soil types. Though the abundance of cathedral mounds were comparable to those found in Africa, the study found that the number of lenticular mounds was more than thrice that of cathedral mounds. It is also one of the few to show that the ability of termites to mix the soil is severely underestimated by not considering lenticular mounds.

This study has debunked several globally accepted theories about termites, possibly due to the bias in the location of study. It also highlights the need for more systematic studies on termites in the south Indian forests, a biodiversity hotspot. “Termite diversity and their symbiotic association with their fungus have been well studied but their impacts on soil dynamics, soil properties, erosion, soil fertility, carbon storage, water infiltration, etc. remains virtually unknown in Asia. This research tries to address some of these”, remarks Dr. Jouquet.