The town I live in is mainly an educational centre boasting a university and many schools. There are no heavy polluting industries and so the air is clean and clear. Lichens are well known as indicators of air pollution for they get their moisture and nutrients from the surrounding environment via air and rain. Fence posts in the country are laden with lichen
A wide variety of lichen grows on the trees in our garden. I understand that lichen is not actually parasitic, but merely uses the trunk or branches for support. Lichen is a combination of an algae and a fungus, the latter providing a structure for the algae to live in while the algae provides food for the fungus.
Studies have indicated that lichen growth rates range from less than a millimetre to a few centimetres every year, and their longevity has been estimated to be in the range of decades or even centuries. I value the presence of lichen in my garden not only for the variety that grows here – which is fascinating – but because I have observed several birds, notably white-eyes and sunbirds, using lichen for their nesting material.
Further interesting information on lichens can be found at: