‘Community evolves slowly in rainforests like India’s Kudremukh and Silent Valley’

Meghna Krishnadas is a senior scientist at the CSIR Centre for Cellular and Molecular Biology (CCMB), India. Speaking to Times Evoke, she explains what drives the diversity of a rainforest community:

I am fundamentally a community ecologist — I study how species get together to form a community. When you walk into a forest, you won’t see just one species of trees, you’ll see many. Part of my research explores why so many diverse kinds of trees exist there and why one species doesn’t dominate.

BETWEEN EARTH AND SKY: India has lush rainforests in the Western Ghats. Photo Courtesy: M. Krishnadas & https://cafelab.in/home/




There is incredible diversity in a forest ecosystem — tropical rainforests in South America or Southeast Asia could have 800 to 1,000 different species in one hectare alone. This varies, depending on the history of how species evolved over time and climate. There will be different levels of diversity between a forest in India, Borneo or Panama — but many of the processes that maintain such diversity remain the same. As a scientist, I am very interested in these.



Some processes include the ‘niche’ of the species or the resources they use. Trees are relatively simple creatures — they need light, water and some nutrients. The question is, do all species use these resources at the same level? The answer is no — therein lies one explanation of how so many different species can coexist. Some species have grown to do well in bright sunshine, some thrive where the forest is really dark and some like dappled sunshine. In complex ecosystems like tropical rainforests, these differences play a large role in preventing any one species from becoming dominant. Even these simple dimensions of light, water and soil nutrients can lead to species differentiating along an available space. This happens over time — in one year, one species does very well, in another year, another thrives. So, when you walk into a forest, you see the result of processes that have played out over decades at least, if not millions of years.

THE SEEDS OF TIME: CCMB scientists plant, tend and study rainforest species. Photo Courtesy: M. Krishnadas & https://cafelab.in/home/

Another key role in enabling diversity is played by the small organisms that eat plants and regulate which trees manage to produce more progeny or seedlings. A tree makes lots of seeds and many get eaten or carried far away — but many also fall right under the parent tree and sit there, facing ‘natural enemies’ or insects and fungi that eat these. Disease-causing pathogens also increase where there are large gatherings of seedlings. But while those seedlings become vulnerable thus and are often cleared out by predators, other species can then come in and establish themselves in that space. If you scale this up through time, you’ll see any species of older, more abundant tree offers more opportunity to its natural enemies. This explains why abundant species at times tend to experience a decline in their population, compared to a rare species, whose seedlings can more easily escape its enemies. This interaction between plants, insects and fungi also plays a critical role in ensuring that no one species becomes dominant and a community is upheld.



Scientists are now investigating whether human actions are impacting these complex interactions. Some effects are visible in a ‘human-modified forest’ — once a very large place, which has now been chopped up into smaller pieces for agriculture, roads or logging. Anthropogenic impacts on how plants interact with their natural enemies are more visible near forest edges as compared to interiors. One of my Masters students recently published research comparing the ability of rodents like porcupines and wild rats to eat seeds in an impacted fragment versus a less disturbed forest — the research shows how their ability to do so increases in the former, which has implications for the future of plant communities.

THE UNDERSTORY HAS A STORY: The undergrowth in a rainforest tells a fascinating tale of evolution and survival. Photo Courtesy: M. Krishnadas & https://cafelab.in/home/

The preservation of rainforests is vital, given their enormous importance in Earth’s biogeography. These are also sanctuaries of nature’s evolutionary history. I’ve been very moved by the Silent Valley national park in Kerala which has a rich conservation history, a people’s movement stopping a dam and creating a national park there. I also love the Kudremukh national park in Karnataka, one of the first rainforests I saw in the Western Ghats. It has beautiful, diverse systems, rainforests below, grasslands and sholas in the upper regions. These places make you realise the dazzling diversity of a rainforest community — and how important it is to protect this.

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