Lichens as indicator species
Lichens are unique composite organisms formed by the symbiotic relationship between fungi and algae, found in a variety of habitats, including trees, rocks, and urban structures. They come in three main forms: crustose, foliose, and fruticose, each contributing to ecosystems by providing food and habitat for various animals. Due to their sensitivity to environmental changes, lichens serve as important indicator species, often referred to as "canaries in the coal mine." Their growth rates are extremely slow, often less than 5 millimeters per year, which allows researchers to use them to track environmental changes over time, especially in relation to climate change and pollution.
Lichens have been crucial in long-term climate studies, as their presence and growth patterns can reveal historical and current climatic conditions. Through techniques such as lichenometry, scientists measure the size of lichen patches to estimate the age of surfaces they inhabit, helping document the effects of global warming. For example, species like Rhizocarpon, commonly found in Arctic regions, have been instrumental in these studies, indicating shifts in temperature and the impact of climate change on their populations. Overall, lichens are vital for understanding ecological health and responding to environmental challenges.
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Lichens as indicator species
Definition
Lichens are very common organisms found in widely diverse habitats, including rock surfaces, trees, and human-made structures. Lichens use structures on which they grow as hosts to support their growth. They are composites, composed of two different organisms, an alga and a fungus, resulting in a symbiotic organism that has a morphology very different from the two original organisms. In lichen symbiosis, the alga provides energy through photosynthesis and the fungus provides protection and support. Lichens come in three types: crustose, a crusty form that grows tightly on rocks or trees; foliose, which resembles foliage; and fruticose, which has the appearance of “fingers.” Lichens provide food for animals, such as reindeer living in arctic regions, and habitat for invertebrates. Lichens absorb nutrients from air and rain and are an important part of nutrient recycling. They grow very slowly, with rates less than 5 millimeters per year. Some species even have growth rates of less than 0.5 millimeter per year. Lichens often live for long periods of time, with some species in the arctic estimated to be over five thousand years old.
Significance for Climate Change
Because of their sensitivity to environmental factors, including temperature changes, lichens can serve as indicator species (or canaries in the coal mine) to predict environmental changes. Historically, lichens have been important indicators of pollution and climate changes. Many long-term climate change studies have used lichen growth to estimate changes in environmental temperature over time. Mapping the distribution of climate-sensitive species provides an indication of current climatic conditions, whereas monitoring over time reveals past climate change effects. Lichen growth studies have been an important part of the debate over greenhouse effects by providing data that support climate change and global warming. Because of global warming, arctic-alpine species have been diminishing, while more tropical species have flourished.
Lichens grow at very slow rates, increasing in diameter as they grow. The size of individual lichen patches on rocks can be used to estimate age, with measuring the diameter of the largest lichen on a rock surface a method to determine the time period during which that rock was exposed. The study of lichen growth to determine the age of, or to “date,” surfaces is called “lichenometry.” The slow growth and longevity of crustose lichens have made them especially useful in lichenometry. Measurement of lichens has been used to document effects of global warming, such as glacial deposits, former extent of persistent snow cover, and avalanche activity. Most climate change studies using lichens have been conducted using a group of crustose lichens of the genus Rhizocarpon, which is very abundant in many Arctic environments.