Lichen succession on Cecropia spp. trunks in a lower montane wet secondary forest Megan M. Smith College of Literature, Science and Art, University of Michigan ABSTRACT Cecropia spp . are common pioneer tree species in regenerating forest ecosystems and are often covered in trunk colonizers such as lichen, moss, and vines. As the tree ages and a more mature forest closes in, the microhabitat becomes darker and wetter, thus forcing species to change along a vertical species gradient as the succession of epiphytes tends more toward vascular plants. This study looks at epiphytic succession by measuring the percent lichen cover at a constant height on the trunks of Cecropia spp. It was hypothesized that percent lichen cover would decrease as tree diameter in creased. One hundred trees were surveyed and percent lichen cover was measured at breast height and crude overall lichen cover was estimated. Lichen cover was found to decrease significantly with increased diameter, supporting the hypothesis. The results from this study indicate that the microhabitat on Cecropia tree trunks changes over time, becoming less suitable to lichens. RESUMEN Cecropia spp son especies comunes de Ã¡rboles pioneros que regeneran ecosistemas de bosque y a menudo se cubren con coloni zadores de troncos tales como lÃquenes, musgos y enredaderas. Cuando el Ã¡rbol envejece y un bosque mÃ¡s maduro se desarrolla, el microhÃ¡bitat se vuelve mÃ¡s oscuro y hÃºmedo, forzando asÃ a las especies a cambiar en una sucesiÃ³n vertical que va de las epifÃta s no vasculares a las plantas vasculares. Se estudiÃ³ la sucesiÃ³n de las epifÃtas midiendo el porcentaje de cubierta de lÃquenes a una altura constante en los troncos de Cecropia spp . Se predijo que el porcentaje de cubierta de lÃquenes disminuirÃa con el aumento en el diÃ¡metro del Ã¡rbol. Se inspeccionaron cien Ã¡rboles en los que se midiÃ³ el porcentaje de cubierta de lÃquenes a la altura del pecho y se estimÃ³ la cubierta general de lÃquenes. La cubierta de lÃquenes disminuyÃ³ significativamente con el aumen to del diÃ¡metro, apoyando la hipÃ³tesis. Los resultados de este estudio indicaron que el microhÃ¡bitat en los troncos de guarumo cambia con el tiempo, volviÃ©ndose menos hospitalario para los lÃquenes. INTRODUCTION Lichens are often the first organisms to c olonize newly exposed surfaces (Shaw and Goffinet 2000), especially when there is high light availability. Such surfaces include trees in disturbed forest habitat or regenerating, abandoned pastures. Mosses and other bryophytes are also common pioneers, b ut require a less windy microhabitat and continuous moisture (Shaw and Goffinet 2000). These conditions can develop as the open area matures and gains denser canopy and understory vegetation. Some lichen are specific to tree species due to texture, moist ure holding capacity, and chemistry, which may change as the tree ages (e.g. maple bark softens and becomes more absorbent as the tree ages) (Brodo et al. 2001). In one study, isolated chemicals from lichen tissue extractions were found to strongly inhibi t seed germination (Sedia and Ehrenfeld 2003), and may inhibit the growth of other competitors on the tree trunk. However, mosses persist due to their longevity, tolerances of desiccation and extreme temperatures, and modest nutrient requirements (Shaw an d Goffinet 2000). This may be the reason why they succeed lichens especially when the microhabitat of the understory
becomes more suitable for mosses. Thus, lichens must compete for substrates, especially in the moist, high altitude tropics with faster g rowing and larger epiphytes such as bryophytes (Brodo et al. 2001). Competition can increase over time as the trees age and simultaneously become part of an increasingly dark, dense, and moist understory forest ecosystem, conducive for bryophytic growth. Hence, the aging bark undergoes a microhabitat change, which in turn affects what types of epiphytes will thrive and form a persisting community. The increasing shade may make it difficult for the photobiont to photosynthesize and supply the fungi part o f the lichen symbiosis with carbohydrates, forcing the colonies to move higher up the trunk to reach more sunlight. Indeed, trees at maturity have been found to support distinct vertical zones of epiphytic communities, perhaps resulting from successional progression of epiphytes as the host tree ages (Shaw and Goffinet 2000). The lifespan of the tree becomes an important factor to take into consideration, especially com munity at the trunk base is usually dominated by facultative epiphytes, such as bryophytes (Shaw and Goffinet 2000). Eventually, bryophytes build up an organic layer, increasing nutrient availability and making the site suitable for the colonization of va scular plants. These vascular plants in turn alter the microenvironment further, making it especially difficult for the initial colonists to survive (Schofield 1985). In addition to vines and lianas, plants with more developed and distinct vascular tissue , (e.g. epiphytes, such as aroids, orchids, and bromeliads), take advantage of the moist substrate and may even inhibit the presence of bryophytes. Sedia and Ehrenfeld (2003) found that moss dominance was negatively correlated with higher vascular plant d ensities. A study of Eucalyptus obliqua in Tasmania found that lichen species richness was positively correlated with tree diameter (Kantvilas and Jarman 2004). They found that succession in the epiphyte communities usually involved a gradual replaceme nt of species, from pioneer to climax, accompanied by a vertical shift in species distribution, the pioneers being replaced as the trees aged. Cecropia spp. are excellent pioneer trees in areas of regenerating forest due to their very fast growth in heig ht and broad leaves which maximize the capture of available sunlight (Janzen 1983). White crustose lichen patches cover the trunks of Cecropias found in abandoned pastures, light gaps, and other disturbed areas. Cecropias were an appropriate species to e xamine in this study due to their presence in gaps and recovering forest and their abundant lichen cover. There are 17 identified genera of lichen at this C. obtusifolia , C. peltata, C. polyphlebia ) (Haber 2000). Little is known on epiphytic succession in tropical ecosystems, which is unique in having high epiphytic diversity especially in the favorable climate of continuously moist high altitude montane forests. This s tudy looks at epiphytic succession by measuring the percent lichen cover on the trunks of Cecropia spp. It was hypothesized that percent lichen cover would decrease as tree diameter increased.
METHODS AND MATERIALS This study was conducted in the for est around the EstaciÃ³n BiolÃ³gica de Monteverde, Puntarenas, Costa Rica, along the trails Sendero Gongolona and Sendero Quitirri (fig. 4). The forest close to the EstaciÃ³n BiolÃ³gica is on the Pacific slope in the lower montane wet forest life zone with an elevation of 1400 1800 m (Haber et al. 2000). The forest contains patches of primary and secondary forest. Data were collected July 21 st through August 2 nd , 2005. All Cecropia spp . up to 30 m off the two trails were observed regardless of tree size or l ocation. Diameter of Cecropias was measured at breast height (DBH, 1.3 m) using a measuring tape. Percent lichen cover was measured by applying a transparency printed with a grid of 10 x 20 1 cm squares on the north side of each tree at breast height and counting the number of squares containing lichen. Only squares containing all or over 50% lichen were counted. The color of the lichen species was also recorded along with the content of other squares, such as vines. Lastly, overall percent cover was es timated by visually assessing the entire visible portion of the trunk. A Spearman Rank test was run to see if percent lichen cover was a function of DBH (since the DBH data were not normally distributed and could not be transformed to meet that assumptio n). A separate Spearman Rank test evaluated overall percent cover and DBH. Since a secondary observation while taking data was that trees with larger DBH had darker lichen, a Kruskal Wallis Test was used to assess significance. RESULTS Data were taken from 100 Cecropia trees with diameters ranging from 3 33 cm, x = 12.3, +/ 0.9 ) All lichen found were of the crustose growth form, and six different color morphs were found with green and dark green being most prevalent, which may be indicative of diff erent species. The data reflects that vines were found growing on trunks of all different DBH, but a trend in visual observations was that of vines more often populating trunks of larger DBH. Percent lichen cover was significantly negatively correlated wi th DBH (Spearman Rank R s = 0.431, p < 0.0001) (Fig. 1). The estimate of total lichen cover was also significantly negatively correlated with DBH (R s = 0.435, p = 0.0001) (Fig. 2). The Kruskal Wallis test between DBH and lichen color found a statisti cally significant difference (H = 42.108, p < 0.0001) and is shown visually in an interaction bar plot (Fig. 3). The 6 different observed colors were ranked numerically (0 = white, then fades through green, darkening to black), and the test found that the re was a statistically significant difference between mean DBH found of trees that contained a certain color. While collecting data, other possible trends were observed such as white lichen being associated with Cecropias with more light exposure. Also, older trees with little or no lichen were predominantly covered with moss, and were found deeper in the forest. DISCUSSION Percent lichen cover decreased with increasing DBH, supporting the predicted trend for this study, as well as the results found by Kantvilas and Jarman (2004). The decrease in
lichen cover as tree DBH increases may be influenced mainly by the changing microhabitat in an increasingly dense understory as the forest as a whole matures. A denser canopy decreases light availability to t he lower portion of the tree trunk, and the shade sustains a higher moisture content in the air and on substrates due to the lack of sunlight to cause evaporation. As the tree ages, DBH increases, as does surrounding moisture content and shade, which are more suitable conditions for moss than lichens, which are out competed and forced to colonize further and further up the tree trunk. Green lichens were found lower and white found higher along the trunk, which could indicate a possible replacement tendenc y, based on which microclimate conditions were most suitable to the specific lichen species. Based on current knowledge, the correlations found coincide with previous studies and with the proposed general theories of epiphytic succession. There are severa l possible reasons that mosses succeed lichens on Cecropia tree trunks. As the understory closes in, the microhabitat is darker, more moist, and protected from wind, which is more ideal for moss growth. Also, with increased DBH, the tree trunk gains more girth, which allows more space for larger epiphytes to grow, as well as a more developed moisture and light gradient (Kantvilas and Jarman 2004). This information was supported by the observed trend in which vines were found only on trees with large DBH and heavy moss cover, and implies the successional order of vines after moss, possibly because of the more nutrient rich substrate and climbable surface. There is still much to be studied about epiphytic succession on tree trunks of tropical species. Th is is an important area of study in relation to conservation implications because lichens are well known indicators of air pollution because of their ability to utilize the water (and suspended particles) in especially moist air. Additionally, epiphytes c an affect soil composition and concentration of nutrients by absorbing trickling or ambient water (fog), and they absorb and release water after a rain, thus influencing humidity level in the ecosystem (Brodo et al. 2001), which make them even more vital s tudy subjects. For future research, it would be helpful to study percent cover over a longer temporal period to gain insight on the successional pattern of different lichen species. Diameter at breast height is not the most accurate method of measuring tree age, due to genetic variability, suppression, and other site factors (Kantvilas and Jarman 2004), so a different method should be used, perhaps involving the trunk nodes characteristic to Cecropias. Also, trees over a larger geographic range and reg eneration stages could better indicate differences between mature and recently disturbed forests. If percent be illustrated, as well as the succession of different lic hen species and their distribution along the trunk according to microhabitat. Perhaps most importantly, future studies should measure percent moss cover as well as lichens, in order to more specifically illustrate the order of epiphytic succession on the tree trunk. ACKNOWLEDGEMENTS Special thanks to Carlos Guindon for being a supportive project consultant, and to Mark Wainwright for the hours of brainstorming assistance. Thanks and big hugs to Maria Jost for her endless patience and assistance with sta tistical analysis, and to Nathaniel Talbot for reminding me that my study had to have actual biological relevance. Thanks also to La EstaciÃ³n BiolÃ³gica de Monteverde for providing living
quarters and access to surrounding forest, and CIEE for the research supplies, books, and instruments. I give much gratitude to the bottomless coffee pots and the gracious cooks who operated them, and Enigma in my walkman is solely responsible for drowning out the bad banjo music constantly playing in the computer room. Las tly, Sheiphali Gandhi is the only reason why I am not currently clinically insane. LITERATURE CITED Brodo, I. M., S. D. Sharnoff, S. Sharnoff. 2001. Lichens of North America, pp. 3 60. Yale University Press, London, England. Haber, W. A., W. Zuchowski , and E. Bello. 2000. An introduction to cloud forest trees Monteverde, Costa Rica, p. 11, 170. Mountain Gem Publications, Monteverde de Puntarenas, Costa Rica. G.S. Hartshorn. 1983. Trema micrantha. In D. H. Janzen (Ed.) Costa Rican Natural History. Univ ersity of Chicago Press, Chicago, Illinois. pp. 337. Kantvilas, G. and S. J. Jarman. 2004. Lichen and Bryophytes on Eucalyptus oblique in Tasmania: management implications in production forests. Biolgical Conservation 117 (4): 359 373. Schofield, W. B. 1 985. Introduction to Bryology, p. 323. The Blackburn Press, Caldwell, New Jersey. Schneyer, Rachel. Spring 1998. Common lichen genera of San Luis and Monteverde. Tropical Ecology and Conservation. CIEE. pp. 8. Sedia, E. G. and J. G. Ehrenfeld. 2003. Li chens and mosses promote alternate stable plant communities in the New Jersey Pinelands. Oikos 100 (3): 447 458. Shaw, A. J. and B. Goffinet. 2000. Bryophyte biology, pp. 270 271. Cambridge University Press, Cambridge, United Kingdom.
Fig. 1 . Re lationship between DBH and percent lichen cover on Cecropia spp. from standardized grid counts on north side of trees at 1.3 m from ground. (Spearman Rank, R s = 0.431, p < 0.0001) Fig. 2 . Relationship between DBH and overall percent lichen cover. (Spearman Rank R s = 0.435, p < 0.0001)
Fig. 3 . Interaction Bar Plot for mean DBH and mean rank of lichen color (0 = white, then fades through green, darkening to black).
Fig. 4 . Map of the forest around La EstaciÃ³n BiolÃ³gica de Monteverde, Puntarenas, Costa Rica. Shaded area indicates region from which data were collected.
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Una mayor diversidad de hongos en la vertiente atlntica del Bosque Nuboso de Costa Rica
Greater diversity of fungi on Atlantic slope of Costa Rican cloud forest
Biodiversity in much of the Neotropics is impacted by windward/leeward effects. North
East trade winds dump moisture as they hit the mountains, creating a wetter Atlantic
slope, and a drier more seasonal Pacific slope. These factors often favor higher
biodiversity for a given taxon on the Atlantic slope. Fungi were collected between the two slopes of the Monteverde Cloud Forest. A total of 130 fungi specimens were
collected from 1550 meters on both slopes of the Continental Divide to 1750 m. As predicted, fungal species richness (Pacific = 24 species, Atlantic = 39 species), abundance (Pacific = 40, Atlantic = 90), and diversity (H Pacific = 1.55, H Atlantic = 3.44) were significantly higher on the Atlantic slope than on the Pacific. It was also found that the two slopes, though in close proximity, have almost entirely different fungal communities. The results indicate that the climatic factors of high precipitation and lower seasonality caused by windward/leeward effects greatly effect fungal species diversity and composition.
La biodiversidad en la mayora de los neotrpicos es afectada por los efectos de la direccin de los vientos. Los vientos del este depositan la humedad en las montaas del atlntico, creando un atlntico ms hmedo y un pacfico estacional ms seco. Estos factores a menudo favorecen una mayor biodiversidad a un determinado taxn en la vertiente atlntica. Colect hongos en las dos vertientes del bosque nuboso de Monteverde, Costa Rica. Un total de 130 hongos fueron encontrados en los trayectos entre los 1550 y 1750 metros. Como era de esperarse la riqueza de especies de hongos fue mayor en el atlntico (Pacfico=24 especies, Atlntico=39) al igual que la abundancia (Pacfico = 40, Atlntico =90) y la diversidad (H Pacfico=1.55, H Atlntico=3.44). Tambin se encontr que a pesar de la proximidad de los sitios, tienen dos comunidades muy distintas de hongos. Los resultados indican que los factores climticos como la precipitacin y la estacionalidad afectan la composicin de las comunidades de hongos.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Spring 2010
Ecologa Tropical Primavera 2010
t Monteverde Institute : Tropical Ecology