Lichens

Dr Mary Gibson works at the School of Life and Environmental Sciences, Deakin University. Her research interests include the reproductive biology and ecology of algae, bryophytes and lichens. She has been recognised as an inspiring lecturer and her skills became evident as she revealed the importance of lichens to the ecology of the natural environment illustrated by many photographs.

Mary began with a story of a baby hippopotamus which had survived a tsunami. The baby hippopotamus was housed in a pen at a Kenyan zoo and developed a bond with a 130 year-old giant tortoise in. They remained together until the hippopotamus grew to big. During this time they developed an oral communication.

This story was used as an illustration of lichens being a relationship between alga and a fungus. 15,000-20,000 fungi and 40 alga are involved in forming lichens. The fungus provides the structure of the lichen but needs to receive some of the carbohydrates which the alga manufactures by photosynthesis. The alga can live alone but the fungi depend on the alga.

Lichens grow in a wide range of habitats. We were shown lichens growing in marine, Antarctic and mountainous areas. In Nambia, a lichen field growing close to the coast, receives nutrients blown by wind from a seal colony. Trees, soil, rocks and man-made structures are all substrates for lichens. Lichen growth on roof tops, graveyards, metal posts and grindstones is used for dating of objects. Some lichens have very specific requirements – one species grows only on Myrtle Beech trees.

There are three common forms of growth. Crustose lichens growth flat on a substrate and are hard to remove. Foliose lichens are leafy and fructicose lichens are branched. Lichens come in many colours mainly red, yellow, orange, green and grey.

Identification of lichen species is often difficult because of variation within one species in size, thickness, colour and the presence or absence of reproductive structures. Accurate identification often requires microscopic examination, use of chemicals that stain different colours and electrophoresis to separate chemicals in the lichens.

Lichens have a variety of roles in ecology. Small invertebrates can live in lichens and become food for larger organisms. Loss of lichens has lead to decrease in bird biodiversity. Roof top lichens are home to 215 species of lichen moths. Cladia species, a fruticose lichen can be detected under snow by reindeer and is an import source of winter food.

Research is being done to find chemicals in lichens which can be used as insect repellents, sunscreens and new medicines.

The cryptogamic crust (made of algae, lichens and moss) is important in binding soils in arid areas.

Lichens fix nitrogen from the atmosphere in a form that is used by plants.

Lichens are useful organisms for bio-monitoring and bio-indication because they quickly show symptoms of changes in the environment. Forest dieback occurs slowly over time but lichen populations change quickly. Lichens are sensitive to air pollution. Only crustose lichens are found in inner city areas with lichen diversity increasing as air quality improves. Different lichens absorb different pollutants.

Archaeology can use lichens which specific habitat or environmental requirements help to determine conditions is past times.

Lichens, and their alga and fungus components, can reproduce sexually and asexually. Lichen propagules are small and easily distributed by winds. This results in a large number of cosmopolitan species of lichens found in countries around the world. In Australia there is a great deal not known about lichen distribution. Thirty-seven species new to Victoria were found during a rain forest field trip.

In response to questions, Mary said that lichen growth on trees is not a sign of poor tree health. Healthy trees have lichen. Study of fires in the central highlands indicate that fire frequency has increased during the last 50 years leading to increase in wattles which are more fire prone and a decrease in lichen diversity. More study is needed to learn more of the relationship between lichens and the environment.

We thank Mary for her interesting and wide-ranging talk on lichens to the Field Naturalists Club of Ballarat.

Some images of loacl lichens can be seen in the Field Report  “Patterns in Lichens”

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