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For the evaluation of factors affecting lichen distribution, scientists have carried out research in various climatic conditions. Lichen containing specific features and structures can be termed as organisms of air pollution. This is because they are vulnerable to air pollutants such as sulphur dioxide or they can be biomonitors in tracing heavy metal build-up. Lichen species are proven to have the ability to withstand extreme weather conditions. These conditions include humidity, light, and temperature variations. Habitat and other environmental factors play a big role in determining lichen distribution. Due to the fact that lichen is a poikilohydric organism, it is very reactive to microclimatic environmental variations. Lichen manifestation on a tree is affected by physical and chemical properties of the tree. Environmental variations such as light, humidity, and temperature affect lichen distribution in an ecosystem (Horvat & Fajon 2011). The following paper describes lichen infestation, environmental factors affecting lichen distribution, and the environmental effects it creates in an ecosystem.
Figure 1a shows lichen growing on a cedar, while Figure 1b shows lichen on an oak tree. In this process, two trees which have lichen on their stems are used. This method involves placing a 5 cm grid square on the bark of each tree and counting each grid where lichen occurs. For Figure 1a, the count is 13, while for Figure 1b, the count is 8. The compass provides directions. The point of the compass must be clearly and precisely determined.
Environmental factors such as tree height, tree diameter, altitude, and exposure to light affect lichen distribution both positively and negatively. Lichen infestation varies from one species to another depending on the age of the tree and its increasing height and diameter (Horvat & Fajon 2011). Microclimatic conditions and the surface of the bark of the tree influence the pattern and distribution of lichen. The vulnerability factors and the bark pH level dictate the lichen alignment. Lichen species tend to be dense where the tree span is increasing, as opposed to bryophytes (Horvat & Fajon 2011).
It can be hypothesized that lichen grows equally on all sides of the tree if there are favourable climatic conditions. This is because environmental conditions dictate the distribution of lichen in an ecosystem. The population of thalli has a direct correlation with the diameter of the stem.
Mutations in photosynthetic processes are vital pointers of lichen reaction to stress. Environmental conditions and underlying features of lichen thalli should be taken into consideration (Pirintsos & Loppi 2011). Climate change has affected photosynthesis and plant yields through disrupted environmental conditions. The symbiotic state of lichen enables it to resume metabolic processes any time when there is adequate hydration. Their survival is enhanced by their ability to absorb nutrients and water from the atmosphere (Pirintsos & Loppi 2011).
Photosynthesis can be inhibited by high light intensity. On the other hand, this light can facilitate photoprotective mechanisms. High light intensity affects temperature and the rate of evaporation. The combination of these environmental factors is what is faced by lichen in the environmental context (Pirintsos & Loppi 2011). Species of lichen are proved to withstand high temperatures. However, the temperature above 35 degrees results in the disruption of photosynthesis. In addition, respiration and photosynthesis depend on the content of water in thallus.
Lichen species being poikilohydric are dependent on water from external sources and their photosynthetic process occurs even in dry areas, which is an indicator of a regular water source. The morphology of thalli and other mycobiont adaptations stands for particular aspects which play a vital role in enhancing external conditions, thereby determining various responses and susceptibility to the ecosystem (Pirintsos & Loppi 2011). According to research conducted in the Mediterranean area concerning the biological environment, there are sensitive organisms in dry areas. In the assessment of biological effects, climatic gradients should be taken into consideration. Transplanted lichen varies along the altitudinal gradient.
Use of Lichen in Scientific Studies
Lichen species have been used extensively in biomonitoring evaluations because of their cost effective implements for planning temporal and three-dimensional patterns of atmospheric pollution and contamination (Williamson & Purvis 2008). Lichen species have the ability to accumulate metals and chemicals in wet or dry particle deposition. These metallic traces are found on thallus surfaces as demonstrated under the electron microscope. Large metal particles accumulate in thalli bringing about the bulk concentration of such metals near industrial areas (Wiliamson & Purvis 2008).
Epiphytic lichen (Hypogymnia physodes) is commonly used in monitoring lichen-related studies because of its extensive distribution and its ability to withstand metals and sulphur dioxide. Where there is extreme pollution, transplants can be used. The purpose of this study is to determine the efficacy of lichen transplant in the process of quantification of atmospheric deposition in a specified area (Williamson & Purvis 2008).
Lichen species are relevant to the above studies because their transplants offer a comprehensive methodology in the percentage assessment of major source contribution within a very short period. Lichen transplants present a brief recording of atmospheric deposition for mining sectors, which is important in the valuation short duration monitoring studies. In addition, the transplant method can be used where human health is not taken into consideration. However, in this case, it does not provide a means that is cost effective or effective in the valuation of the atmospheric admission of contaminators in the environment in a specific area (Williamson & Purvis 2008).