Agasthya 5.2 Forests in flux?

Forest vegetation comprising trees, shrubs, herbs and other plant forms are resources for many animals and human in the forest. Various environmental factors shape the vegetation and changes in these factors will have implications on the functioning of the forest. In fact the forest one sees today is the cumulative outcome of various anthropogenic, environmental and ecological interactions over thousands of years.

Forests change very slowly and to record such changes one needs to monitor the species, their abundance and spatial occurrences at regular intervals. Ascertaining the distribution of species at a point in time is good to judge the conservation status of the species. But to take informed conservation decisions based on a sound understanding of the changing patterns of forest growth, and dynamics of plant communities, long term monitoring is necessary.

The wet evergreen forest in Kalakad Mundanthurai Tiger Reserve (KMTR) is considered as one of the most pristine forests in the Western Ghats. It has several plant species that are endemic to the Agasthyamalai region. We initiated a systematic study on the trees and shrubs at Kakachi in KMTR which is a relatively under explored stretch of wet evergreen forest. The forests at Kakachi had exceptionally low levels of tree diversity compared to most other wet evergreen forests. The forest was dominated by few tree species like Cullenia exarillata, Palaquium ellipticum and Aglaia bourdillonii. Interestingly one of the most abundant species A. bourdillonii turned out to be a localized endemic tree. In the adjacent forest, where selective logging and clear felling were carried out about 40 years ago, we observed that the forest is still recuperating from the disturbance as seen by the high abundance of short-lived, light loving tree species compared to undisturbed forests. To further understand the processes that shapes the forest community in Kakachi, we set up three 1-ha permanent long term monitoring plots.

After 18 years of monitoring these plots, our results show that changes in the composition and abundance of trees over these years is very low compared to other tropical forest sites. Only one of the plots which had a small elevation gradient and a forest opening colonized by reed bamboo, showed greater changes in the abundance of plant groups. On the other hand comparison of plant species and their abundances in undisturbed forests with regenerating forests indicate that high levels of disturbance leads to greater changes in abundance but minimal natural disturbance leads to low turnover of species and could this lead to low number of species?. We also wonder whether the high rate of girth increment in few dominant primary forest species such as Cullenia exarillata and Palaquium elipticum could be the reason for them to monopolize the stand? The plots being located in high altitude forest and susceptible to vagaries of both the monsoons, long term monitoring of changes in vegetation in such plots can throw more light on our understanding of impacts of climate change on forest at a regional level.

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