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Savidge, Jennifer D.
La riqueza y la diversidad de la familia de epfitas vasculares y escaladoras en el dosel de un bosque lluvioso montano bajo en Costa Rica
Family richness and diversity of vascular epiphytes and climbers in the canopy of a lower montane wet forest, Costa Rica
Many studies have been done regarding vascular epiphyte communities in the tropics, however all of the previous studies have neglected the canopy branch tips due to their limited accessibility (Nieder et al. 2004, Freiberg and Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram and Nadkarni 1993). The purpose of this study was to evaluate differences in family richness, and diversity of previously unstudied branch tip epiphyte communities vs. those of secondary branch bases. Data were gathered about community composition of vascular epiphyte families and climbers on the branch tips of canopy trees in a Neotropical, lower montane rainforest in Costa Rica. Branches were accessed from suspension bridges ranging from 32-65 m, in Selvatura Park, Costa Rica. The number of individuals from each family and total branch area covered by each family were recorded. Branch tip and base communities were compared using S, H, E, N, and Smarg parameters (Magurran 1988), and diversity indices were compared using a t-test. Additionally a pair-wise comparison was carried out on each branch base and tip pair using a sign test (Ambrose et al. 2002). Counts of number of individuals per family were deemed to be inaccurate due to the difficulty in identifying individual ferns. As such, coverage area data were used to draw conclusions. Branch tips (H = 0.27) were found to have a significantly higher diversity than branch bases (H = 0.71) (p-value < 0.001). However, branch bases were found to have a significantly higher family richness even when differences in abundance were controlled for. It was noted that almost all branches surveyed showed high dominance of the Division Pteridophyta on both branch bases and tips. Future studies of epiphyte communities in canopy branch tips should address the issue of identifying individual ferns when root systems are covered in humus and bryophyte mats, as was observed in this study.
Muchos estudios se han hecho con respecto a las comunidades de epfitas vasculares en los trpicos, no obstante todos los estudios anteriores han descuidado las puntas de las ramas en el dosel debido a su limitada accesibilidad (Nieder et al 2004, Freiberg y Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram y Nadkarni 1993). El propsito de este estudio fue evaluar las diferencias en la riqueza de las familias, y la diversidad de las comunidades de epifitas en las puntas de las ramas del dosel, contra los de las bases secundarias de la rama.
Text in English.
Ephiphytes--Ecology--Costa Rica--Puntarenas--Monteverde Zone
Cloud forest ecology--Costa Rica
Epfitas--Ecologa--Costa Rica--Puntarenas--Zona de Monteverde
Ecologa del bosque nuboso--Costa Rica
Tropical Ecology 2008
Ecologa Tropical 2008
t Monteverde Institute : Tropical Ecology
Family richness and diversity of vascular epiphytes and climbers in the canopy of a lower montane wet forest, Costa Rica Jennifer D. Savidge Dept of Biology, Oregon State University ABSTRACT Many studies have been done regarding vascular epiphyte com munities in the tropics; however all of the previous studies have neglected the canopy branch tips due to their limited accessibility Nieder et al. 2004, Freiberg and Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram and Nadkarni 1993. T he purpose of this study was to evaluate differences in family richness, and diversity of previously unstudied branch tip epiphyte communities vs. those of secondary branch bases. Data were gathered about community composition of vascular epiphyte familie s and climbers on the branch tips of canopy trees in a Neotropical, lower montane rainforest in Costa Rica. Branches were accessed from suspension bridges ranging from 32 65 m, in Selvatura Park, Costa Rica. The number of individuals from each family and t otal branch area covered by each family were recorded. Branch tip and base communities were compared using S, H , E, N, and Smarg parameters Magurran 1988, and diversity indices were compared using a t test. Additionally a pair wise comparison was carrie d out on each branch base and tip pair using a sign test Ambrose et al. 2002. Counts of number of individuals per family were deemed to be inaccurate due to the difficulty in identifying individual ferns. As such, coverage area data were used to draw con clusions. Branch tips H = 0.27 were found to have a significantly higher diversity than branch bases H = 0.71 p value < 0.001. However, branch bases were found to have a significantly higher family richness even when differences in abundance were c ontrolled for. It was noted that almost all branches surveyed showed high dominance of the Division Pteridophyta on both branch bases and tips. Future studies of epiphyte communities in canopy branch tips should address the issue of identifying individual ferns when root systems are covered in humus and bryophyte mats, as was observed in this study. RESUMEN Muchos estudios se han hecho con respecto a comunidades vasculares del epÃfitas en los trÃ³picos , no obstante todos los estudios anteriores han descuid ado las puntas de las ramas en el dosel debido a su limitada accesibilidad Nieder y otros 2004, Freiberg y Freiberg 2000, Zotz y otros 1999, Hietz 1997, Freiberg 1996, Ingram y Nadkarni 1993. El propÃ³sito de este estudio fue evaluar diferencias en la riq ueza de familias, y diversidad de las comunidades de epÃfitas en las puntas de las ramas del dosel, contra los de las bases secundarias de la rama. Los datos fueron recopilados sobre la composiciÃ³n de la comunidad de las familias de epÃfitas y de plantas t repadoras en las extremidades de la rama de los Ã¡rboles en un Bosque pluvial Montano Bajo en Costa Rica. Las ramas fueron alcanzadas desde los puentes en suspensiÃ³n que se encontraban entre los 32 65 m, en el parque de Selvatura, Costa Rica. El nÃºmero de i ndividuos de cada familia y el Ã¡rea total de la rama cubierta por cada familia fueron registrados. Utilizando los parÃ¡metros S, H', E, N y Smarg se compararon a las comunidades de la punta y de la base de la rama Magurran 1988, y los Ãndices de la divers idad fueron comparados usando una prueba T. Adicionalmente se utilizÃ³ una comparaciÃ³n pareada entre la base y la punta de las ramas utilizando una prueba de muestra Ambrose y otros 2002. El nÃºmero de individuos por la familia fue determinado para ser ine xacto debido a la dificultad en la identificaciÃ³n de helechos individuales. Como tal, los datos del Ã¡rea de la cobertura fueron utilizados para extraer conclusiones. Las puntas de la ramas H = 0.27 presentan significativamente una mayor diversidad que la base de las ramas H = 0.71 < del p valor; 0.001. Sin embargo, las bases de la
rama fueron presentan una mayor riqueza de familias incluso cuando las diferencias en abundancia fueron controladas para esto. Se observÃ³ que casi todas las ramas examinadas demostraron la alta dominancia de la de la divisiÃ³n Pteridophyta en ambas, puntas y bases. Futuros estudios en las comunidades de epÃfitas en las puntas de las ramas deben considerar el hecho de la identificaciÃ³n individual de helechos cuando el sistema r adical estÃ¡ cubierto en humos y briofitos, como se observÃ³ en este estudio. INTRODUCTION Tropical forests host the highest diversity of vascular epiphyte species in the world. They may comprise up to 50% of tree and leaf biomass in some montane rainfore sts Ingram and Nadkarni 1993. Epiphytic organic matter plays an important role in the ecology of tropical rainforests by absorbing precipitation from rain and fog, capturing and retaining minerals and pollution from the air, and influencing the microclim ate in the canopy Freiberg and Freiberg 2000, Ingram and Nadkarni 1993. Rain forest canopies are also highly dynamic ecosystems, prone to frequent disturbance. This aspect may help to explain the high species richness in these ecosystems. Disturbances ca n help prevent any one species from dominating and open up space for new colonization, which fosters greater diversity Hietz, 1997. In their study of the spatial distribution of vascular epiphytes in a lowland rainforest, Nieder et al. 2004 noted that horizontal distribution was non random. Similarly, other studies have found that there is a gradient of epiphyte growth that occurs laterally along branches with highest amounts of growth occurring close to the base of the tree Freiberg and Freiberg 2000 , Hietz 1997, Freiberg 1996, Ingham and Nadkarni 1993. In all of these studies it was asserted that differences in epiphyte distribution were the result of bryophyte and humus build up required for germination and nutrient acquisition, as well as branch s ize, angle, and age. Results have consistently shown that the highest species richness and abundance of vascular epiphytes is found on older, larger, substrate covered branches, which seem to provide the optimum environment for colonization Ingham and Nadk arni 1993. Many studies have been done regarding vascular epiphyte communities in the tropics; however, previous studies have neglected the canopy branch tips due to their limited accessibility Nieder et al. 2004, Freiberg and Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram and Nadkarni 1993. Although branch tips have not been studied, previous results lead me to hypothesize that there is a difference in diversity, family richness, and abundance between secondary branch tips and branc h bases in the canopy of lower montane rainforests. It was predicted that a higher abundance, richness, and diversity of vascular epiphyte families would be observed on canopy branch bases than on branch tips, as the decreased size and age of branch tips d o not provide the optimum micro habitat for epiphyte colonization. For this study data were gathered on the diversity, richness, and abundance of vascular epiphyte families and ferns on the branch tips of canopy trees in a Neotropical, lower montane rainf orest in Costa Rica. Branch tip data were compared to data collected from the base of the contiguous secondary canopy branches. Hemiepiphytes and climbers were included in this study, as much of their life cycle occurs under the same conditions as true epi phytes Ingram and Nadkarni 1993. The purpose of this study was to evaluate differences in family richness, and diversity of branch tip epiphyte communities vs. those in secondary branch bases.
METHODS Study Site The site was situated on the Atlantic slope of the TilarÃ¡n mountain range in Costa Rica. Data were collected in Selvatura Park, on the Atlantic slope elevation 1600 m where forest consists of intervened, secondary growth, lower montane rainforest. The site receives 3 m to 8 m of rain annua lly, and the mean annual temperature ranges between 12 and 17 ÂºC Haber, 2000. Access to the canopy was achieved by a series of suspension bridges ranging in height from thirty two to sixty five meters off the ground. Sampling Method Branch samples were chosen based on level in the canopy, branch base diameter, branching angle, and proximity to the bridges. Tree species were not taken into account. Only trees comprising the uppermost level of the canopy were surveyed. A total of 12 branches were sampled. All were secondary branches with diameters between 8 cm and 20 cm with branching angle no more than 45 degrees from horizontal. Epiphyte growth on the first meter from the branching point and the last meter from the branch tip was surveyed for each branc h. Diameter and length measurements were visually estimated. Diameter measurements were taken for the base of the branch and the thickest part of the branch tip. The one meter sample sites at the branch bases were assumed to be regular cylinders and the on e meter branch tip sites were assumed to be regular cones for the purpose of calculating surface area. Epiphyte and climber angiosperm families were identified by morphological characteristics with the aid of binoculars and a digital camera. Ferns Divisi on Pteridophyta were identified only to the Division level, The number of individuals present from each family or Division, in the case of ferns and the branch surface area covered by each family was recorded for each base and tip respectively. Because many ferns can reproduce by vegetative budding or send up new shoot from rhizome runners Moran 2004, and because roots and bases of epiphytes were often obscured by bryophyte growth, continuous mats of fern growth were considered as a single individual f or the purpose of this study. Data were collected from July 15, 2008 through August 2, 2008. Statistical Analysis The parameters of species richness S, Shannon Wiener diversity index H , evenness E, abundance N and Margelef index of species richn ess Smarg were calculated using standard methods and equations Magurran 1988. However, in this report, S and Smarg are referred to as F and F marg to denote that epiphytes were identified to the family level or to division in the case of ferns, not to the species level. Parameters were computed for the number of individuals per family observed in the meta community all 12 branches sampled and for the surface area covered by each respective family in the meta community. The meta community H diversity indices for branch bases and tips
were compared using t tests. Additionally, pair wise comparisons were performed on each of the 12 sample branches using a sign test Ambrose et al. 2002. The pair wise comparison was performed based on relative numerical abundances. RESULTS Results from meta community analysis based on relative numerical abundance of each family or division in the case of ferns show strong evidence to indicate that branch bases H = 1.66 have a higher diversity than branch tips H = 1.17 p = value < 0.001. Evenness E was very similar for branch bases E = 0.63 and tips E = 0.65, but abundance, family richness, and Margelef index of family richness were all higher in branch bases Figure 1. Conversely, results from the meta community analysis based on relative area of coverage suggest that there is strong evidence to indicate that branch tips H = 0.71 are more diverse in coverage than branch bases H = 0.27 p value < 0.001. Evenness is greater in branch tips, but fami ly richness, total area covered, and Margelef diversity index was greater in branch bases than in tips Figure 2. All results from the pair wise comparison Table 1 corroborated previous results, with the exception of the Margelef index of family richn ess F marg. The sign test results for Fmarg indicate that there is not a significant difference in family richness on Branch bases vs. branch tips when differences in abundance are controlled for. DISCUSSION The comparison of family diversity using rel ative numerical abundance offers a result that conflict with the family diversity using relative areal abundance. The former indicates that the branch base diversity is greater, whereas the latter says that the diversity of branch tips is higher. Since f amily richness remains constant for both of these tests, the conflicting results are the product of differences in family evenness between the different regions of a branch Figures 1 and 2. The unevenness of aerial coverage in both branch locations can b e explained by the dominance of Pteridophyta. Many of the branches sampled were covered in dense mats of fern growth, however these mats were observed to cover a greater proportion of the branch surface on bases than on tips. Many species of Pteridophyta h ave the ability to reproduce by vegetative budding, or send up new shoots from creeping rhizomes Moran 2004. Since roots and bases of epiphytes are often obscured by bryophyte growth on branches, it is impossible to distinguish individual plants in a den se mat Freiberg 1996. For this reason, continuous mats of fern growth were considered as a single individual in this study. As a result, relative numerical abundance of ferns was likely underestimated. Since the Shannon Wiener diversity index takes into account richness and evenness, the outcome of such an error could be a false conclusion of greater diversity in branch bases than tips. Therefore relative area measurements were deemed to be more accurate. As such, more emphasis is placed on the results o f that meta community analysis and the conclusion was drawn that branch tips have significantly higher family diversity than branch bases. The conclusion reached here can be supported by the previous findings that individuals on branches less than 6cm in diameter experienced higher turnover rates than
individuals living on larger branches Heitz 1997. More frequent disturbances in branch tips may lead to higher mortality rates, which may inhibit any one species from dominating the area, and thus increasin g the overall diversity on branch tips compared to branch bases Hietz, 1997. Relative area for branch tips and bases were both dominated by ferns, followed by orchids. However, in both cases the relative coverage of orchids was more than eight times les s than that of ferns, and the next most abundant family covered about three times less area than orchids. Table 2. These results are not congruent with results from Ingram and Nadkarni 1993 in which they found no strong dominance in angiosperm species. However, ferns were not considered in their study, and it was conducted at a lower elevation on the Pacific slope of the TilarÃ¡n mountain range, which may have markedly different climate than the Atlantic slope site studied here. It was also observed tha t, in general, less of the total surface area of the branch tips was covered by epiphytic growth. In contrast, many of the branch bases sampled were completely covered in large fern mats. Therefore, fern coverage was more dominant on branch bases than bran ch tips, leading to the lower evenness noted in the meta community analysis based on relative area. This observation of higher fern coverage on branch bases is corroborated by previous studies. Heitz 1997 found that ferns and orchids tend to grow in high er abundance on thicker branches. While Freidberg 1996 proposed that smaller branches have lower richness and abundance because their decreased branch top surface area leads to a high instance of epiphyte growth slipping off of the branch. Although dive rsity was found to be higher on branch tips, branch bases had a higher family richness figure 1 and Figure 2. Only 6 out of the 15 families including the division Pteridophyta observed were found on branch tips, while all but one family Asteraceae wa s found on branch bases Table 2. These results have been corroborated by results of past studies. Freiberg 1996 found that species richness was highest at the base of branches in the middle of the crown. However, while both meta community analyses illu strate that branch bases have higher family richness than branch tips Figure 1 and Figure 2, results of the pair wise comparison imply that there is no difference in family richness between branch bases and tips table 1. This discrepancy is most likely the result of limitations in the sign test analysis. The sample size of 12 branch tip/base pairs is small, and sign tests do not pick up subtle differences. For this reason overall interpretation of species richness and Fmarg should be based on meta popul ation calculations, not on the sign test calculations. Therefore, it can be concluded that branch bases displayed an overall higher family richness than branch tips. All other results from the pair wise comparison corroborated the meta population results Table 1. Future investigations may wish to address the experimental limitations of this study by physically identifying the exact number of Pteridophyta species present on each sample branch. However, obtaining a definite number of fern individuals woul d require physical access to canopy branch tips as well as removal of the bryophyte substrate, and thus would be difficult to achieve and would heavily impact the microhabitat. It is also worth noting that although fern growth dominated the surface area of both branch bases and branch tips, most large fern mats were comprised of short, delicate ferns that did not seem to obscure growth of larger vascular epiphytes. If disturbing the habitat is not an
issue, future studies may choose to follow techniques out lined by Ingram and Nadkarni 1993, in which branches are stripped and species abundance and diversity is compared based on dry weight. During data collection it was observed that branches without much moss cover tended to have less epiphytes growing on t hem. These results were consistent with previous observations that scarcity of bryophytes and humus build up impedes epiphyte colonization and succession Nieder et al. 2004. Bryophyte coverage provides a medium for epiphytes to germinate and take root an d Substrate characteristics determine the composition and availability of resources. In the future a study could be conducted to test the relationship between epiphyte growth and the type or thickness of bryophyte coverage for the upper canopy and branch t ips. Freidberg and Freidberg 2000 found that the thickness of bryophyte and humus cover was generally higher on larger, central branches than on smaller peripheral branches. They proposed that the lower species richness and abundance found in the periphe ry of the crown is due to low amounts of humus and bryophyte cover on the branches. A study on the effects of bryophyte colonization on branch tip epiphyte communities would be particularly interesting, as high exposure to abiotic pressures and increased r ate of disturbance may result in a tight correlation between moss coverage and vascular epiphyte succession Freiberg 1996. This study was designed as a preliminary attempt to collect branch tip epiphyte data that has never been accessed before. Family r ichness results are congruent with the results from previous studies. However the conclusion that branch tips have higher diversity than branch bases runs counter to the trends noted in previous epiphyte reports. This conclusion could change if data at the species level was collected, as the more in depth sat could pick up differences in species richness that did not register at the family level. Future studies are encouraged to gather additional branch tip data, identifying individuals to the species level , if access allows, in order to gain more in depth insight into the little known world of canopy branch tips. ACKNOWLEDGEMENTS I am indebted to Karen Masters for her help in identifying epiphyte families, technical support, invaluable advising, and all around expertise in the field of epiphyte ecology. I would like to thank Selvatura Park for granting me permission to conduct this research from their canopy bridges. I am grateful in advance to Jose Carlos Moncho Calderon for assisting me with the co mposition of a Spanish resumen. Additional Thanks to CIEE and the Monteverde Biological Station for providing resources for data collection and analysis. Literature Cited Ambrose, H. W., K. P. Ambrose, D. J. Emlen, and K. L. Bright. 2002. A handbook of biological investigation. Hunter Textbooks Inc., Winston Salem, North Carolina. Freiberg, M., E. Freiberg. 2000. Epiphyte diversity and biomass in the canopy of lowland and montane forests in Ecuador. J. Trop. Ecol. 16: 673 688. Freiberg, M. 1996. Sp atial distribution on vascular epiphytes on three emergent canopy trees in French Guiana. Biotropica. 28: 345 355.
Haber, W. A., Plants and vegetation. In N. M. Nadkarni, and N. T. Wheelwright Eds.. Monteverde, Ecology and Conservation of a tropical cl oud forest, pp. 39 94. Oxford Univ. Press, New York, New York. Hietz, P. 1997. Population dynamics of epiphytes in a Mexican humid montane forest. J. Ecol. 85: 767 775. Ingram, S. W., N. M. Nadkarni. 1993. Composition and distribution of epiphytic organi c matter in a Neotropical cloud forest, Costa Rica. Biotropica. 25: 370 383. Magurran, A. E. 1988. Ecological diversity and its measurement. Princeton Univ. Press, Princeton, New Jersey. Moran, R. C. 2004. A natural history of ferns. Timber Press Inc, Po rtland, Oregon. Nieder, J., S. Engwald, M. Klawun, and W. Barthlott. 2000. Spatial distribution of vascular epiphytes including hemiepiphytes in a lowland Amazonian rain forest Surumoni crane plot of southern Venezuela. Biotropica. 32: 385 396. Zotz, G. P. Bermejo, H. Dietz. 1999. The epiphyte vegetation of Annona glabra on Barro Colorado Island, Panama. J. Biogeography. 26: 761 776.
A. Family Richness F 0 2 4 6 8 10 12 14 16 Branch Base Branch Tip Location on Branch number of families B. Shannon-Wiener Diversity Index H' 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 Branch Base Branch Tip Location on Branch H' diversity index C. Evenness E 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Branch Base Branch Tip Location on branch Evenness D. Abundance N 0 50 100 150 200 250 300 Branch Base Branch Tip Location on branch Number of individuals E. Margalef index of family richness Fmarg 0 0.5 1 1.5 2 2.5 Branch Base Branch Tip Location on branch Fmarg Figure 1. Summary results of F, H', E, N and Fmarg for the number of individuals per family observed on branch bases vs. branch tips. A Overall Branch bases had higher family richness than branch tips. B The Shannon Weiner diversity index shows a higher diversity of epiphyte families on branch bases. C The evenness was very similar f or branch bases and branch tips. D Branch bases were observed to have a higher abundance of individual epiphyte plants than branch tips. E The Margelef index of family richness revealed that branch bases are more diverse than tips, even when difference s in abundance are controlled for. Based on 12 branches.
A. Family Richness F 0 2 4 6 8 10 12 14 16 Branch Base Branch Tips Location on branch Number of families B. Shannon-Wiener diversity index for area H' 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 Branch Base Branch Tips Location on branch H' diversity index C. Evenness of coverage E 0 0.1 0.2 0.3 0.4 0.5 Branch Base Branch Tips Location on branch Evenness of coverage D. Total area covered by epiphyte growth N 0 5000 10000 15000 20000 25000 Branch Base Branch Tips Location on branch Area covered cm2 E. Margelef index of family richness Fmarg 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Branch Base Branch Tips Location on branch Fmarg Figure 2. Summary results of F, H', E, N and Fmarg using relative area covered of epiphyte coverage on branch bases vs. branch tips, for 12 branches. A Overall there wer e more families represented branch bases than branch tips. B The Shannon Weiner diversity index for area covered suggests that branch tips are more diverse in their coverage than branch bases. C Evenness of coverage was greater in branch tips than in b ranch bases, although neither location showed high overall evenness. D The total area covered by epiphyte growth was higher in branch bases than branch tips. E The Margelef index of family richness shows that even when differences in the coverage area are controlled for, branch bases still have greater family richness than branch tips.
Table 1. Results of pair wise comparisons sign test of branch bases vs. branch tips for all branches sampled. To the right are the significance values for each comparison. All values corroborate previous results with the exception of Fmarg. Community index Number + Number Number Ties Significance F 10 0 2 P < 0.05 H 11 1 0 P < 0.05 E 7 5 0 P > 0.05 N 10 1 1 P < 0.05 Fmarg 8 4 0 P > 0.05 Table 2. F amilies and division in the case of ferns observed on sample branches, including two unidentified epiphytes. The right hand columns represent the relative area covered by each family on branch tips and bases respectively. Family or Division Branch bas es cm Branch tips cm Orchidaceae 386 111 Bromeliaceae 145 41 Ericaceae 103 71 Pteridophyta 18192.23 975.58 Araceae 150 0 Cyclanthaceae 35 0 Cluseaceae 38 0 Melastomataceae 2 0 Rubiaceae 20 0 Smiliaceae 10 0 Gesnariaceae 5 0 Asteraceae 0 2 Piperaceae 5 5 Unknnown #1 3 0 Unknown #2 5 0 Total area covered 19099.23 1205.58