Research was conducted in the FACE Station located in UKM Fernarium, The National University of Malaysia (02˚55'20.3"N 101˚46'59.4"E). FACE Station in UKM Fernarium was programmed automatically to release CO₂ into the surroundings at fluctuated concentration. A computer-control system uses the wind speed and CO₂ concentration information to adjust the CO₂ flow rates to maintain the desired CO₂ concentration at the centre of the FACE ring. The system uses the wind direction information to turn on only those pipes upwind of the plots, so that CO₂-enriched air flows across the plots, no matter which way the wind blows. When wind speeds are low (<0.4 m/s) and direction is difficult to detect, the CO₂-enriched air is released from every other vertical pipe around the ring. The CO₂ flow rate is updated every second, and the choice of which vertical pipes to release from is updated every 4 seconds. Three different distances (20 m, 50 m and 80 m approximately) were selected to depict the effects of CO₂ on lichen distribution (Figure 1).

Lichen samples were collected in FACE Station and from its 80 m perimeters. All epiphytic lichen specimens were identified using a stereomicroscope and chemical spot tests, a UV lamp, and TLC following the standard checklists of Sipman in Singapore [6] .

Lichen diversity frequencies were determined using quadrate (20 cm × 50 cm). For each sampling points, 20 trees were selected randomly to evaluate lichen species distribution frequency. Lichen was sampled by each wind directions at approximately 3 meters height. Only trees with circumference around 60 - 120 cm selected to conduct the sampling. Sampling was conducted in three different distances (20 m, 50 m & 80 m) [7] .

Every data recorded was analyzed using statistical analysis Shannon’s Diversity Index and Evenness to understand the diversity’s rate of lichen species at FACE Station and its surrounding. Lichen species frequency density also analyzed using graphical analysis ArcGIS 10.3 to evaluate the distribution of lichen species based on its frequency [7] [8] .

Seven species of lichen were identified and divided into three genera. All of them belong to crustose groups: Cryptothecia striata, Cryptothecia scripta, Cryptothecia granularis Cryptothecia subtecta, Porina tetracea, Myriotrema minutum and one unknown species labelled as crustose 1. All lichen been found were identified and matched with Sipman (2009) publication from Singapore. All lichen’s picture that has been found in FACE station were shown in Figure 2.

From 20 trees from each sampling locations, Table 1 shows the lichen species been found, the frequencies for each species from each location, the species diversity index (H) and the evenness value (E). Figure 3 shows the frequencies distribution for each of lichen species for all sampling locations graphically.

Based on Figure 3, the highest frequencies for all species is Cryptothecia striata with 35% at FACE Station, 21% at 50 m from FACE Station and 80 m from FACE Station. Followed by Cryptothecia granularis, Cryptothecia scripta, Porina tetracea, Myriotrema minutum, Cryptothecia subtecta and the lowest is Crustose 1 with 6.5% frequency and only can be found at 80 m from FACE Station. It shows that there are significant differences in the frequencies of lichen species in term of CO₂ effects. Increase in CO₂ concentration (inside FACE Station) unequivocally also increase the rate of photosynthesis occurred inside lichen’s photobiont. In general, photosynthesis process needs CO₂ and water in order for the process run in optimal condition. That’s the reason why frequencies of lichen species that exist inside FACE Station were much higher compare to 50 m from FACE Station and 80 m from FACE Station.

In term of diversity, different CO₂ concentration affected lichen diversity substantially. Lichen diversity increased gradually when receding the FACE Station. According to species diversity index (H) in Table 1, the value of the index increased from FACE Station is 1.35, 50 m from FACE Station 1.53 and 80 m from FACE Station is 1.89. Increase in CO₂ concentration affected several of lichen’s growth such as Cryptothecia scripta, Cryptothecia subtecta and Crustose 1. These three species only existed outside the FACE Station. The difference in lichens distribution shows that lichens get affected with the elevation of CO₂. The elevation of CO₂ concentration acidified the bark of tree which is important for epiphytic lichen attachment. The rhizine of lichen only recognize particular pH of substrate. Changes in pH bring no growth for that particular of lichens.