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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 epip hyte communities in the tropics, however all of the previous studies have neglected the canopy branch t ips due to their limited accessibility (Nieder et al. 2004, Freiberg and Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram and Nadkar ni 1993). The purpose of this study was to evaluate differences i n family richness, and diversity of previously unst udied branch tip epiphyte communities vs. those of second ary 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 to tal branch area covered by each family were recorded. B ranch 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 individu als 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 signif icantly higher diversity than branch bases (H = 0. 71) (p-value < 0.001). However, branch bases were found to have a significantly higher family richness eve n when differences in abundance were controlled for. It was noted that almost all branches surveyed show ed high dominance of the Division Pteridophyta on both branch bases and tips. Future studies of epiphyte communities in canopy branch tips should address th e 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 comunid ades vasculares del epfitas en los tropicos, no obstante todos los estudios anteriores han descuida do las puntas de las ramas en el dosel debido a su limitada accesibilidad (Nieder y otros 2004, Freibe rg y Freiberg 2000, Zotz y otros 1999, Hietz 1997, Freiberg 1996, Ingram y Nadkarni 1993). El propsit o de este estudio fue evaluar diferencias en la riq ueza de familias, y diversidad de las comunidades de ep fitas en las puntas de las ramas del dosel, contra los de las bases secundarias de la rama. Los datos fueron recopilados sobre la composicin de la comunidad de las familias de epfitas y de plantas trepadoras en las extremidades de la rama de los rboles en un Bosqu e pluvial Montano Bajo en Costa Rica. Las ramas fuero n alcanzadas desde los puentes en suspensin que se encontraban entre los 32-65 m, en el parque de Selv atura, Costa Rica. El nmero de individuos de cada familia y el rea total de la rama cubierta por cad a familia fueron registrados. Utilizando los parme tros 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 ndices de la diversidad fueron comparados usan do una prueba T. Adicionalmente se utiliz una comparacin pareada entre la base y la punta de las ramas utilizando una prueba de muestra(Ambrose y otros 2002). El nmero de individuos por la famili a fue determinado para ser inexacto debido a la dificultad en la identificacin de helechos individ uales. Como tal, los datos del rea de la cobertura fueron utilizados para extraer conclusiones. Las puntas de la ramas (H = 0.27) presentan significativamente u na 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 familia s incluso cuando las diferencias en abundancia fuer on controladas para esto. Se observ que casi todas la s ramas examinadas demostraron la alta dominancia d e la de la division Pteridophyta en ambas, puntas y base s. Futuros estudios en las comunidades de epfitas en las puntas de las ramas deben considerar el hecho de la identificacin individual de helechos cuando el si stema radical est cubierto en humos y briofitos, como se observ en este estudio. INTRODUCTION Tropical forests host the highest diversity of vasc ular epiphyte species in the world. They may comprise up to 50% of tree and leaf biomass in some montane rainforests (Ingram and Nadkarni 1993). Epiphytic organic matter plays an important role in the ecology of tropical rainforests by absorbing precipitation fro m rain and fog, capturing and retaining minerals and pollution from the air, and influencin g the microclimate in the canopy (Freiberg and Freiberg 2000, Ingram and Nadkarni 19 93). Rain forest canopies are also highly dynamic ecosystems, prone to frequent distur bance. This aspect may help to explain the high species richness in these ecosyste ms. Disturbances can help prevent any one species from dominating and open up space for n ew colonization, which fosters greater diversity (Hietz, 1997). In their study of the spatial distribution of vascu lar epiphytes in a lowland rainforest, Nieder et al. (2004) noted that horizontal distribution was nonrandom. Similarly, other studies have found that there is a gradient of epiphyte growth that occurs laterally along branches with highest amounts of gr owth occurring close to the base of the tree (Freiberg and Freiberg 2000, Hietz 1997, Freib erg 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 size, angle, and age Results have consistently shown that the highest species richness and abundance of vascu lar epiphytes is found on older, larger, substrate covered branches, which seem to p rovide the optimum environment for colonization Ingham and Nadkarni 1993). Many studie s have been done regarding vascular epiphyte communities in the tropics, howev er, previous studies have neglected the canopy branch tips due to their limited accessi bility (Nieder et al. 2004, Freiberg and Freiberg 2000, Zotz et al. 1999, Hietz 1997, Freiberg 1996, Ingram and Nadkar ni 1993). Although branch tips have not been studied, previou s results lead me to hypothesize that there is a difference in diversity family richness, and abundance between secondary branch tips and branch bases in t he canopy of lower montane rainforests. It was predicted that a higher abundan ce, richness, and diversity of vascular epiphyte families would be observed on canopy branc h bases than on branch tips, as the decreased size and age of branch tips do not provid e 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 rainforest in Costa Rica. Branch tip data were compared to data collected from the base of the contiguous secondary canopy br anches. Hemiepiphytes and climbers were included in this study, as much of their life cycle occurs under the same conditions as true epiphytes (Ingram and Nadkarni 1993). The p urpose of this study was to evaluate
differences in family richness, and diversity of br anch tip epiphyte communities vs. those in secondary branch bases. METHODS Study Site The site was situated on the Atlantic slope of the Tilarn mountain range in Costa Rica. Data were collected in Selvatura Park, on the Atlan tic slope (elevation 1600 m) where forest consists of intervened, secondary growth, lo wer montane rainforest. The site receives 3 m to 8 m of rain annually, and the mean annual temperature ranges between 12 and 17 C (Haber, 2000). Access to the canopy was a chieved 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 ca nopy, 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 ca nopy 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 branchi ng point and the last meter from the branch tip was surveyed for each branch. D iameter 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-me ter sample sites at the branch bases were assumed to be regular cylinders and the one-me ter branch tip sites were assumed to be regular cones for the purpose of calculating sur face area. Epiphyte and climber angiosperm families were ident ified by morphological characteristics with the aid of binoculars and a di gital camera. Ferns (Division 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 a nd tip respectively. Because many ferns can reproduce by vegetative budding or send u p new shoot from rhizome runners (Moran 2004), and because roots and bases of epiphy tes were often obscured by bryophyte growth, continuous mats of fern growth we re considered as a single individual for 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-Wie ner diversity index (H), evenness (E), abundance (N) and Margelef index of species ri chness (Smarg) were calculated using standard methods and equations (Magurran 1988). How ever, in this report, S and Smarg are referred to as F and Fmarg to denote that epiph ytes were identified to the family level (or to division in the case of ferns), not to the s pecies level. Parameters were computed for the number of individuals per family observed i n 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 ind ices for branch bases and tips were compared using t-tests. Additionally, pair-wis e comparisons were performed on each of the 12 sample branches using a sign test (A mbrose et al. 2002). The pair-wise comparison was performed based on relative numerica l abundances. RESULTS Results from meta-community analysis based on relat ive numerical abundance of each family (or division in the case of ferns) show stro ng evidence to indicate that branch bases (H = 1.66) have a higher diversity than bran ch 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 f amily richness were all higher in branch bases (Figure 1). Conversely, results from the meta-community analysi s based on relative area of coverage suggest that there is strong evidence to i ndicate 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 family richness, total area covered, and Margelef diversity index was greater in branch bases than in tips (Fig ure 2). All results from the pair-wise comparison (Table 1) corroborated previous results, with the exception of the Margelef index of family richness (Fmarg). 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 relative n umerical abundance offers a result that conflicts with the family diversity usi ng 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 family richness rem ains 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 coverag e in both branch locations can be explained by the dominance of Pter idophyta. 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 have the ability to reproduce by veget ative budding, or send up new shoots from creeping rhizomes (Moran 2004). Since roots an d bases of epiphytes are often obscured by bryophyte growth on branches, it is imp ossible to distinguish individual plants in a dense mat (Freiberg (1996). For this re ason, continuous mats of fern growth were considered as a single individual in this stud y. As a result, relative numerical abundance of ferns was likely underestimated. Since the Shannon-Wiener diversity index takes into account richness and evenness, the outco me of such an error could be a false conclusion of greater diversity in branch bases tha n tips. Therefore relative area measurements were deemed to be more accurate. As su ch, more emphasis is placed on the results of that meta-community analysis and the conclusion was drawn that branch tips have significantly higher family diversity tha n branch bases.
The conclusion reached here can be supported by the previous findings that individuals on branches less than 6cm in diameter e xperienced 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 increasing the overal l diversity on branch tips compared to branch bases (Hietz, 1997). Relative area for branch tips and bases were both d ominated by ferns, followed by orchids. However, in both cases the relative covera ge of orchids was more than eight times less than that of ferns, and the next most ab undant family covered about three times less area than orchids. (Table 2). These results ar e not congruent with results from Ingram and Nadkarni (1993) in which they found no strong d ominance 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 Tilarn mount ain range, which may have markedly different climate than the Atlantic slope site stud ied here. It was also observed that, 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. Therefo re, fern coverage was more dominant on branch bases than branch tips, leading to the lo wer evenness noted in the metacommunity analysis based on relative area. This obs ervation of higher fern coverage on branch bases is corroborated by previous studies. H eitz (1997) found that ferns and orchids tend to grow in higher 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 i nstance of epiphyte growth slipping off of the branch. Although diversity was found to be higher on branch tips, branch bases had a higher family richness (figure 1 and Figure 2). Onl y 6 out of the 15 families (including the division Pteridophyta) observed were found on b ranch tips, while all but one family (Asteraceae) was found on branch bases (Table 2). T hese results have been corroborated by results of past studies. Freiberg (1996) found t hat species richness was highest at the base of branches in the middle of the crown. However, while both meta-community analyses illustr ate that branch bases have higher family richness than branch tips (Figure 1 a nd Figure 2), results of the pair-wise comparison imply that there is no difference in fam ily 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 pai rs is small, and sign tests do not pick up subtle differences. For this reason overall inte rpretation of species richness and Fmarg should be based on meta-population calculations, no t on the sign test calculations. Therefore, it can be concluded that branch bases di splayed 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 exper imental 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 would require physical access to canopy branch tips as well as re moval of the bryophyte substrate, and thus would be difficult to achieve and would heavil y impact the microhabitat. It is also worth noting that although fern growth dominated th e surface area of both branch bases
and branch tips, most large fern mats were comprise d 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 techniqu es outlined 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 branche s without much moss cover tended to have less epiphytes growing on them. Thes e results were consistent with previous observations that scarcity of bryophytes a nd humus build-up impedes epiphyte colonization and succession (Nieder et al. 2004). Bryophyte coverage provides a medium for epiphytes to germinate and take root and Substr ate characteristics determine the composition and availability of resources. In the f uture a study could be conducted to test the relationship between epiphyte growth and the ty pe or thickness of bryophyte coverage for the upper canopy and branch tips. Freidberg and Freidberg (2000) found that the thickness of bryophyte and humus cover was generall y higher on larger, central branches than on smaller peripheral branches. They proposed that the lower species richness and abundance found in the periphery of the crown is du e to low amounts of humus and bryophyte cover on the branches. A study on the eff ects of bryophyte colonization on branch tip epiphyte communities would be particular ly interesting, as high exposure to abiotic pressures and increased rate of disturbance may result in a tight correlation between moss coverage and vascular epiphyte success ion (Freiberg 1996). This study was designed as a preliminary attempt to collect branch tip epiphyte data that has never been accessed before. Family ri chness results are congruent with the results from previous studies. However the conclusi on that branch tips have higher diversity than branch bases runs counter to the tre nds 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 rich ness that did not register at the family level. Future studies are encouraged to gather addi tional 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 iden tifying epiphyte families, technical support, inval uable advising, and all around expertise in the field of epiphyte ecology. I would like to thank Selvatura P ark for granting me permission to conduct this research fro m their canopy bridges. I am grateful (in advance) to Jose Carlos Moncho Calderon for assisting me with the composition of a Spanish resumen. Additional Thanks to CIEE and the Monteverde Biological Statio n 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. Spatial 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.). Mon teverde, Ecology and Conservation of a tropical cloud 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: 767-7 75. Ingram, S. W., N. M. Nadkarni. 1993. Composition an d distribution of epiphytic organic matter in a Neotropical cloud forest, Costa Rica. Biotropica. 2 5: 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. Timb er Press Inc, Portland, Oregon. Nieder, J., S. Engwald, M. Klawun, and W. Barthlott 2000. Spatial distribution of vascular epiphytes (including hemiepiphytes) in a lowland Amazonian ra in forest (Surumoni crane plot) of southern Venezuela. Biotropica. 32: 385-396. Zotz, G. P. Bermejo, H. Dietz. 1999. The epiphyte v egetation of Annona glabra on Barro Colorado Island, Panama. J. Biogeography. 26: 761-776.
nr nrnr rrr rrrrr nrnr rrr !"rr" nrnr rr#r #$rr% nrnr rr#r "&'(r((r' nrnr rr#r 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-W einer diversity index shows a higher diversity of epiphyte families on branch bases. (C) The evenness was very similar for 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 differences in abundance are controlled for. Based on 12 branches.
nr nrnr rr#r rrrrr( nrnr rr#r !"rr('" nrnr rr#r )#**'+% nrnr rr#r "&'(r((r' nrnr rr#r 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 were more families represented branch bases than br anch tips. (B) The Shannon-Weiner diversity index for area covered suggests that bran ch tips are more diverse in their coverage than branch bases. (C) Evenness of coverag e was greater in branch tips than in branch bases, although neither location showed high overall evenness. (D) The total area covered by epiphyte growth was higher in branch bas es than branch tips. (E) The Margelef index of family richness shows that even w hen 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 tes t) of branch bases vs. branch tips for all branches sampled. To the right are the signific ance values for each comparison. All values corroborate previous results with the except ion 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. Families (and division in the case of fern s) observed on sample branches, including two unidentified epiphytes. The right-han d columns represent the relative area covered by each family on branch tips and bases res pectively. rrn r nr r r nr!r r "#r r r r r r $ r r r %!#! r & r & r r r r (n!r r r () r r r *!! r r r +) r r r r r r -n r r r '! r r r % r r r .n/nn0nr1 r r r .n/n0nr1r r r !rr# r &&& r r
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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