Host plant specificity of corticolous lichens in urban and suburban New Amsterdam, Berbice, Guyana

In this study, host plant lichen specificity was investigated. Data was collected from 1000m2 sampling plots at each of four locations with an established 50m x 20m plot at each site. Forty-one trees from across five species were examined using (10cm by 50cm) ladder quadrats on tree trunks (N, S, E, W) at 150cm height. A total of 14978 individual lichens were identified that yielded 10 families, 13 genera and 18 species. Swietenia mahagoni showed the highest average corticolous lichen species composition, followed by Terminalia catappa and Melicoccus bijugales respectively. Cocos nucifera had a higher average species recorded than Mangifera indica. Crustose lichens were the most prominent corticolous lichens observed (61%) with the most individuals in Graphidaceae and Arthoniaceae. Foliose lichens (28%) showed the most abundance in Parmeliaceae, Caliciaceae and Collemataceae. Of the taxa recorded, 22.2% were restricted to specific trees. C. parasitica, H. laevigata, U. cornuta were restricted to S. mahagoni. D. applanata was restricted to C. nucifera. 22.2% of recorded species were found on all of the tree hosts that were examined. Bacidia laurocerasi, Flavoparmelia caperata, Flavoparmelia soredians and Graphina anguina. S. mahagoni hosted 88.9% of all recorded species. Swietenia mahagoni showed the highest average of recorded corticolous lichen species of all host trees with 7.58. Mangifera indica showed the lowest average with 4. The maximum number of species (10) was recorded on one S. mahagoni tree.


Introduction
Host plants provide space for different types and species of lichens [1]. Preference is shown by some lichens for certain trees and this may be based on different factors inclusive of the nature of the bark, microclimatic and chemical conditions [2]. It is important to understand host preferences when considering lichen ecology, because of the important roles that lichens play in ecosystems [3] [4] [5] [6].
In addition, an understanding of host specificity of lichens may be useful when considering their diversity and conservation [1]. Although there are many publications on studies done on lichen relationships in other countries [1] and in the tropical forests of Guyana [7] [8] [9] [10] [11] [12] [13] [14] there appears to be a dearth of information available for lichens especially for urban and suburban areas in Guyana.
Epiphytic lichens growing on the surface of plants, are often used as bio-indicators of environmental quality [15] and are also useful as indicators of environmental disturbances [16]. However, lichen data necessary for environmental impact and conservation assessments in rural, urban and suburban areas is somewhat limited for Guyana.
The main objective of this study was to investigate the host tree specificity of corticolous lichens in suburban and urban New Amsterdam. The key research question that was addressed in this study was whether there was lichen-host tree specificity in suburban and urban New Amsterdam.
This study has the potential to add to the body of knowledge of corticolous lichen flora in an urban settlement in Guyana. The results from this study can be a useful baseline to investigate the effects of urbanization on local corticolous lichen biodiversity while helping to inform other assessments and management decisions concerning Guyana's lichen diversity.

Study Area
This study was conducted in New Amsterdam, Berbice, Guyana. Four study sites were identified: two (Site #1 and Site #2) were classified as urban locations and two (Site #3 and Site #4) were classified as suburban locations.

Sampling and Data Collection
Field work was completed during the period February -May, 2019 and data was collected from sampling plots of 1000m 2 at each location where a plot of 50m x 20m was established at each site.
Sampling plots were laid out randomly for sampling and corticolous lichens were only sampled on undamaged trees with a girth of more than 70cm [17] [18].
Ladders measuring 10cm x 50cm and each having five 10cm x 10cm contiguous quadrats were used to sample the tree trunks. Each ladder was placed on the tree trunk on the north, south, east and west directions such that the upper edge of each ladder was 1.5m above the highest point on the ground [19].
Lichen species, their associated host plants and the frequency observed within each of five randomly placed 10cm x 10cm quadrats of the ladder were recorded. Lichen species cover was estimated to the nearest cm 2 and expressed as a percentage of the inspected trunk area [16].

Identification of lichens
Lichen specimen identification was done on the basis of morphological observations of the thalli and apothecia of the corticolous lichens with the use of a magnifying glass. The following were also used for the identification of lichens [

Data Analysis
Statistical analyses and calculations were done using PAST 3.24 Statistical software.

Results
This study focused on investigating lichen -host plant specificity of corticolous lichens at four study sites in New Amsterdam. Lichen specimens were collected from a total of 41 host trees. 14978 lichen specimens were recorded during the study, representing 10 families, 13 genera and 18 species (Table 1). When all sites were considered, crustose corticolous lichens species were the most recorded (61%), while squamulose (5%) and fruticose (6%) were the least recorded (Fig. 2).

Figure 2
Lichen distribution according to type of thallus

Host Tree Specificity
Swietenia mahagoni showed the highest average corticolous lichen species presence, followed by Terminalia catappa and Melicoccus bijugales respectively. Cocos nucifera had a higher average species recorded than Mangifera indica.
Four species of lichens showed specificity towards host trees and four species showed no host specificity and were observed on all five of the tree species sampled. Table 3 and Figure 4 give the species that showed specificity and their associated specific host tree were:

Discussion
All around the world, species appear to be under threats from anthropogenic activities and lichens have been noted among such species. [26] notes that there will be major challenges to humans and biodiversity as a result of climate change. Further, with pending sea level changes that could impact coastal locations, the exclusion of lesser-known yet ecologically important species from assessments of biodiversity can have implications for global and local conservation strategies [27].
The current study location lies within Guyana's coastal Plain which has the potential to be seriously impacted by sea level change. Therefore as [26] [27] have noted, it is important to pay attention to lesser known groups such as lichens as well as the pending implications of sea level change for coastal locations.
A total of 14978 lichen representatives belonging to 10 families, 13 genera and 18 species of corticolous lichens were recorded from these four sites.
The results revealed that 22.2% of all recorded corticolous lichen species were restricted to specific trees. C. parasitica, H. laevigata, U. cornuta were restricted to S. mahagoni and D. applanata were to C. nucifera). 22.2% species were found on all tree hosts: Bacidia laurocerasi, Flavoparmelia caperata, Flavoparmelia soredians and Graphina anguina and S. mahagoni was host to 88.9% of all recorded species.
It should be noted, however, that factors which may influence host specificity, such as bark pH, water content, porosity, degree of bark shading, presence of tree sap [28], were not investigated in this study. Investigating these factors in future research in urban and suburban areas in Guyana could shed light on host plant -lichen specificity and likely offer an explanation as to the reasons for any observed patterns.
Swietenia mahagoni showed the highest average of recorded corticolous lichen species of all host trees with 7.58 and Mangifera indica showed the lowest average with 4. The maximum number of species recorded from a tree was 10 on S. mahagoni trees. This number of species could be due to the fact that only a part of the tree trunk was sampled since different lichen species inhibit varying levels of a tree [29].
Both urban and suburban sites had three species of host trees each. For the urban sites the species were Melicoccus bijugales, Swietenia mahagoni and Terminalia catappa while for the suburban sites the host tree species were Cocos nucifera, Mangifera indica and Melicoccus bijugales. With a decrease in host tree specificity observed at Site #4, there was an apparent decrease in corticolous species richness. Although Site #4 had the lowest number of lichen species (10), this site was the one with the greatest number of individuals.
The results also revealed that 83.3% of all species were encountered in more than one study site. Cladonia parasitica, Hypotrachyna laevigata and Usnea cornuta were however restricted to Swietenia mahagoni trunks in site #1 while Dirinaria applanata was restricted to Cocos nucifera, and was found in sites #3 and #4.

Conclusion
Host plant specificity was observed for four species of the recorded lichens. Three species were specific to S. mahagoni and one species was specific to C. nucifera.
There was a higher number of crustose lichens as compared to foliose, fruticose and squamulose.
There is a need for further studies to examine other parts of the tree to determine if there is a difference in the lichen diversity based on the part of the host plant.
As it pertains to host specificity, future studies should investigate the bark characteristics that are known to influence lichen appearances to see if there is indeed a relationship between lichens and tree hosts.
Lichens are good bio-indicators of ecological health and therefore, studies pertaining to assessing and monitoring ecosystem and environmental health, especially urban areas, can focus on using lichens.
It will be important to also factor the impacts of climate change into any future study of lichens in coastal areas in Guyana.
This study was a preliminary investigation on host-plant lichen specificity in urban and suburban settings in Guyana.
Given that previous research has demonstrated the value of lichens as indicators of air pollution, other studies of this nature in Guyana may be helpful, given that there is much development taking place in urban and suburban areas which can likely increase the instances of pollution.