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A Comparison of Lichen Abundance and Diversity on Trees in Primary Forest, Artificial Edge and Natural Edge

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Susan Hoffmire, Jenelle Hopkins, Centennial High School   Las Vegas, NV Beverly Mowrer, Sedro-Woolley Senior High   Sedro-Woolley , Wa. Susan Sprenke,  Jefferson Junior High School   SW, Washington, DC

Abstract

Lichen samples taken from trees in the interior, natural and artificial edges of the Wilson Forest , located in the premontane rain forest at Las Cruces, Costa Rica, indicate that there may be a difference in lichen diversity and abundance. These differences may be attributed to the abiotic conditions of the three areas. The greatest diversity and abundance was found at the artificial edge, and the least at the natural edge.

Introduction

Lichens are generally described as two organisms that form a mutualistic, symbiotic relationship. These organisms are a fungus and either a green algae, cyanobacteria or blue-green algae. Lichens are classified by their fungus (either Ascomycetes or

Basidiomycetes). The fungus provides the algae with protection and moisture. The algae provide the fungus with carbohydrates, some vitamins and may even fix nitrogen from the air (Campbell 1990). Lichen will grow on any hard substrate and can be found on surfaces such as rocks, trees and leaves. They are categorized by four morphological types; crustose, foliose, fruiticose and squamulose. Lichens can tolerate almost any environment, from tropical rain forest to artic conditions. Their diversity in cool/temperate climates is equaled or surpassed by their diversity on tropical climates (Lucking 1999b). However, they are species sensitive to differing ecosystems. Of the microclimatic abiotic parameters important to lichen growth, light intensity and altitudinal zones seem to have the greatest effect on lichen diversity (Lucking 1999). Because lichens receive nourishment directly from the air, species diversity is studied to determine anthropogenic or natural changes in the ecosystem. These bioindicators are particularly sensitive to climatic changes and atmospheric pollution (Lucking 1997).

Land fragmentation has become in important environmental issue in tropical forests. As primary forests become more fragmented, edge habitat between forest and pasture has increased. This has resulted in changes in abiotic factors along these edge locations. These changes may be causing differences in community flora and fauna near the edge (Holl 1997).

This study examines lichen growth in three locations.

Sampling Method

Lichen samples were taken from trees located in and around the premontane primary rainforest of the Wilson Botanical Gardens. Primary interior forest, natural edge and artificial edge trees were chosen along the Rio Jaba trail. Trees of an unidentified species were chosen because of their distinctive leaf pattern. Until a positive identification of this tree has been made, for the purposes of this study we chose to call it the Jennabev suesu. Tree circumference averaged 31.1 cm. The Jennabev suesu grow very tall and their branching leaf structure can be considered as belonging to the lower part of the canopy cover. A sample of the bark was taken back to the lab and a pH measurement of 9.5 was taken, indicating an alkaline environment for epiphytic growth.

Five trees of the same species and approximately the same circumference in three distinct areas of the forest along the Rio Jaba trail were selected for sampling. It was assumed that the similar circumference size indicated similar ages. It was also assumed that trees in the same area with similar sizes would be exposed to similar abiotic factors that would affect lichen growth. The first sampling set was located at marker _______ along the trail, well into the interior of the primary forest. The next sample set was taken in the open area along the Rio Jaba River. This area was considered the natural edge. The last set was taken along the pasture trail, no more than 20 meters into the primary forest. Trees in this area were considered as belonging to the artificial edge because the forest had been cut down to provides pasture area.

To determine abundance, a belt transect measurement of lichen coverage was taken at approximately 1.5 meters above the ground. A plastic strip marked off in two-centimeter increments was wrapped around the tree trunk and the tree circumference was measured and recorded. Then each section was examined for the presence of lichen growth. Coverage was recorded. Percent coverage was determined by dividing coverage by circumference and multiplying by 100. (See Table 1)

Table 1

Lichen samples were taken at this belt-transect height. A two centimeter wide band of bark was scraped clear of lichen growth. The samples were identified by tree location and placed in a plastic bag for transport to the lab for analysis.

Once in the lab the lichen samples were microscopically examined for their morphological features. Lichen samples for trees in the same sample location were combined. Each lichen sample in each set was first classified according to their morphological features as belonging to one of four types: fruitiose, foliose, squamulose or crustose. Then each sample within these four types was looked at for color or textural differences. These differences were assumed to represent a different morpho-species. Each morpho-species was recorded. (See Table 2)

Table 2

Data Analysis

Although our samples show the highest abundance and diversity of morpho-species of lichen to be on trees measured at the artificial edge, lichens measured in the primary forest showed no significant difference in diversity and abundance. However, the lichens measured at the natural edge showed substantially lower abundance and diversity. (see Chart 1)

The lichen diversity and abundance at the artificial edge are only slightly higher than that within the forest. Both areas showed species richness but the low number of overlapping species clearly indicates species sensitivity to the two microclimates.

 Chart 1

Conclusions

These results were expected for the forest location. The Wilson Forest is a primary forest, carefully protected from human impact. The artificial edge is a pasture that has not been grazed for almost 15 years. Perhaps this absence of human impact has allowed lichens most suitable to the increased light and temperature conditions of the pasture edge to become established and healthy. The lack of lichen growth at the natural edge might reflect the increased humidity of the river’s ecosystem, encouraging competitive moss growth. Most of the trees at this edge were observed to be covered with moss. These conditions may allow the mosses to out-compete the lichens with respect to nutrients and space.

These results complement a study done by the staff biologist at Wilson Botanical Gardens (Quiros 2001). His study indicated greater lichen growth on trees located at the edge of the garden versus trees growing in the center of the garden.

Further studies of this phenomenon can include higher sampling populations, different tree species and different natural edges.