Diversity: not a sure winner

Diversity of species doesn't always help the ecosystem stage a comeback after degradation

By Ghazala Shahabuddin
Published: Sunday 15 April 2001

Its generally assumed that species diversity helps a disturbed ecology to be nurtured back to health. But a recent study has shown otherwise. M Sankaran of Syracuse Universityusahas conducted a study on the disturbance of grasslands in southern Western Ghats. The responses of grasslands to fire and simulated grazing in Mundanthurai plateauTamil Naduwere analysed to gauge the changes caused in species diversity.

The study focussed on the ability of ecosystems to spring back to their original state after a bout of disruption. The disruptions can occur in the form of fire to floods. The recovery of vegetation after disturbance can determine the ability of an ecosystem to support a food chain for dependant organisms. The popular view is that diverse habitats tend to be more stable in face of disturbance. But when the area was subjected to controlled firesthe demarcated plots with high species density were found to respond no beter thatn the ones with lesser number of species. Plots dominated by lime-grass were found to become more stable than other plots. The rapid recovery of lime-grass is attributed to its fast rate of growth. Sankaran's study also demonstrates that the in-built resilience of certain species and habitat types is evidence of their long-term adaptation to human- induced changes in the ecosystem. The tendu tree in the tropical dry forests of the Indian peninsula is an example of species that have adapted to repeated forest fires.

The results of the study has contributed to better management of grasslands in the Mundanthurai region where spread of lime grass has also been linked to a dip in populations of Cheetal deer. The results of the study have shown how repeated fires to control the growth of lime-grass are in fact aiding its perpetuation. The lime grass out grows and dominates all other species during recovery from the fire-ravaged.

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