Question

Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?

Answer 1

Lichens need moist and pollution free environment for their growth. Moreover, they are highly sensitive to sulphurdioxide $\left(S{O}_2\right)$ Delhi has lakhs of automobiles which emithuge amount of $S{O}_2$ in atmosphere. In such a highly pollutedenvironment lichens cannot grow. While in Manali andDarjeeling the environment remains moist throughout theyear and is relatively free from $S{O}_2$ owing to lesser numberof automobiles. This provides favourable conditions for the growth of lichens. Since, lichens are highly sensitive to $S{O}_2$they act as bioindicator.