Lichens, what are Lichens? These are the small round patches, slightly off colored green in the bark of trees in your backyard. They seem profuse in wet months and become dry patches during the summer.

Lichens are actually a combination of a fungal partner (mycobiont) and an algal partner (phycobiont). The fungal filaments surround and grow into the algal cells, and provide the majority of the lichen's physical bulk and shape.

Lichens can grow in soil, rock, or even the barks of trees.  It absorbs certain mineral nutrients from any of these substrates on which it grows, but is generally self-reliant in feeding itself through photosynthesis in the algal cells. Thus, lichens growing on trees do not feed on them like parasites on the trees.

Lichens are indicators of the health of an ecosystem in tropical regimes like our islands, the more the lichen load (in trees etc.,) the more robust is the nutrient cycle of that ecosystem. Several studies have shown serious impacts on the growth and health of lichens resulting from factory and urban air pollution. Because some lichens are so sensitive, they are now being used to quickly and cheaply assess levels of air toxins in Europe and North America.

Andaman & Nicobar Islands have a healthy ecosystem, when compared to other parts of our country. Lichens were seen even in the barks of road side trees of Port Blair city until recently. Though it still exists, of late it seems that Lichens are disappearing from the city limits. This is a matter of concern as they indicate the health of our eco system.

- Amlan Dutta, Ecologist