Lichens are epiphytes occurring in most environments of the world. They are commonly found on soil, trees, leaves, and even bare rock. They are found in mesic environments, potentially long lived and are poikilohydric. They are a product of the symbiotic relationship of photosynthetic acyanobacteria and a fungus (most commonly an ascomycete). The symbiotic relationship may be of various types such as mutualism, commensalism, or parasitism. The outer layer is known as the cortex and is composed of photobiont cells. The inner layer, known as the medulla, is composed of loosely arranged hyphae. Below the medulla is a lower cortex from where the rhizines anchor the lichen to its substrate. Lichen morphology varies and they can appear fructicose, foliose, crusticose or even gelatinous. The bulk of the lichens are produced by the thallus, the reproductive organs are termed apothecia. Lichens reproduce by releasing diaspores that contain both fungal and algal cells. (Ahmadjian 1993
The results in figure 1 show that the highest density of lichens was to be found on the south facing side of the tree trunks. The lowest density of growth was found on the northern side. The east and west sides of the trees seemed to have equal amounts growth.
The results have lead us to reject the null-hypothesis as figure 1 clearly indicates that one side of the tree trunk had higher coverage with lichens.
In order to determine the possible reasons for this we must consider what lichens require for growth. They require a substrate, moisture, and sunlight for the photosynthetic element. Since it is probably safe to assume that the substrate (e.g. the tree trunk) is the same on all sides of the tree, we can reject this is a reason for the underlying growth differences. The moisture levels absent any other factors should be identical, however, the sunlight could effect the micro-environment causing a particular side of the tree more exposed to the sun light to be slightly less moist. Similarly, the variance in the exposure of light of the different surfaces of the tree trunk may affect the photosynthetic growth component of lichens.
A workable hypothesis to test whether it is sunlight or moisture levels would be “if provided with adequate moisture and humidity would lichen growth rates be effected when exposed to direct light.”
Lichens have long been used as models in the study of environmental effects. In the 19th century it was already observed that cities had a lower lichen diversity than the more rural or forested regions. More recently, studies have been undertaken to map lichen communities, to study morphological and anatomical changes caused by pollution, and to study any physiological changes in lichens when exposed to various pollutants. The use of lichen in environmental studies was apparent with the formulation of the Index of Atmospheric Purity (IAP) developed by LeBlanc and De Sloover in 1970.
Lichens are environmental sponges and they aggregate a large variety of environmental toxins in their tissues. They are also very sensitive to a variety of air pollutants such as sulfur, nitrogen, and fluorine containing gases. Different species of lichens have different sensitivities to the various pollutants and the epiphytic types (those that grow on trees) seem to be most sensitive to air pollution.
The phenology of focal species is used to assess the effects of climate change in local environments, worldwide. Species range maps can be compiled using the data collected by studying focal species and then a Climate Change Vulnerability Index (CCVI) can be compiled. The CCVI is composed of 4 parts, 1) direct exposure to local environmental change, 2) indirect exposure to environmental change, 3) species vulnerability to climate change, 4) existing responses to the threat. (Young et al. 2010)
There are relatively few studies, and most involve birds. However, these studies show alarming trends in phenology of various migratory bird species (earlier arrival and later departure), as well as studies showing that certain plants are flowering earlier too (Chambers 2009.)
Recording the phonological stage is important for determining the effects of climate change on species and biodiversity because the life cycles of species are often times dependent on external factors. For instance, the increased heat may be causing the plants to flower early and the birds to shift their migration patterns.
In conclusion, by studying the various species and forms of life on earth we can learn about how climate change is affecting them and in turn how it effects humans. While studies on humans would require ethical approvals and accrue massive costs, studying lichens or observing species is a comparatively simple way for us to acquire data on the effects the climate has on living organisms. The implications are greater than just biodiversity which critics may call irrelevant. Given the genetic similarities of all life on earth, we have much to learn about our own vulnerabilities even from the lowly lichen.
Ahmadjian, V., 1993. The l ichen symbiosis. 2nd. ed. New York: John Wiley and Sons
Chambers, L.E. 2009. Evidence of climate related shifts in Australian phenology? MODSIM09, Cairns, 13-17 July, 2009.
Gries, C. 1996. Lichens as Indicators of Air Pollution. In: T. H. Nash, III, Lichen Biology. Cambridge: Cambridge University Press, pp. 240-254
Young, B., E. Byers, K. Gravuer, K. Hall, G. Hammerson, and A. Redder. 2010.
Guidelines for Using the NatureServe Climate Change Vulnerability Index:
Release 1.2. NatureServe.