UvA-DARE (Digital Academic Repository) Vascular epiphytes in Taiwan and their potential response to climate change Hsu, R.C.C. Publication date 2013 Document Version Final published version Link to publication Citation for published version (APA): Hsu, R. C. C. (2013). Vascular epiphytes in Taiwan and their potential response to climate change. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:10 Oct 2021 Vascular epiphytes in Taiwan and their potential response to climate change Rebecca C.-C. Hsu 2013 UNIVERSITEIT VAN AMSTERDAM Cover: The epiphytic fern Polypodium formosanum growing on a blue glass ball (representing the Earth) to express that species' response to climate change is an entangled question. Back cover: A common scenery of montane cloud forests in the afternoon on Taiwan. Vascular epiphytes in Taiwan and their potential response to climate change Hsu, R. C.‐C. 2013. Vascular epiphytes in Taiwan and their potential response to climate change. PhD thesis, University of Amsterdam, The Netherlands Cover layout: Rebecca C.‐C. Hsu Cover illustration: Rebecca C.‐C. Hsu ISBN: 978‐94‐91407‐12‐3 Vascular epiphytes in Taiwan and their potential response to climate change ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof. dr. D.C. van den Boom ten overstaan van een door het college voor promoties ingestelde commissie, in het openbaar te verdedigen in de Agnietenkapel op dinsdag 10 september 2013, te 10.00 uur door Rebecca Chia‐Chun Hsu geboren te HsinChu, Taiwan Promotiecommissie Promotores: Prof. dr. G.R. de Snoo Prof. dr. J.H.D. Wolf Copromotores: Dr. J.G.B. Oostermeijer Dr. W.L.M. Tamis Overige leden: Dr. J.F. Duivenvoorden Prof. dr. H. Hooghiemstra Prof. dr. S.B.J. Menken Dr. N. Raes Prof. dr. P.H. van Tienderen Faculteit der Natuurwetenschappen, Wiskunde en Informatica CONTENTS 1 General Introduction 6 2 Diversity and phytogeography of vascular epiphytes in a tropical‐subtropical transition island, Taiwan (Flora 204(8), 2009, pp. 612‐627) 16 3 Regional and altitudinal patterns in vascular epiphyte richness on an East Asian island 30 4 Canopy CO2 concentrations and crassulacean acid metabolism in Hoya carnosa in a subtropical rain forest in Taiwan: consideration of CO2 availability and the evolution of CAM in epiphytes (Photosynthetica 44(1), 2006, pp. 130‐135) 48 5 Comparative photosynthetic capacity of abaxial and adaxial leaf sides as related to exposure in an epiphytic fern in a subtropical rainforest in northeastern Taiwan (American Fern Journal 99(3), 2009, pp. 145-154) 60 6 Adaptation of a widespread epiphytic fern to simulated climate‐change conditions 70 7 Simulating climate change impacts on forests and associated vascular epiphytes in a subtropical island of East Asia (Diversity and Distributions 18(4), 2012, pp. 334-347) 86 8 Conclusions 108 REFERENCES 115 APPENDIX 1 139 APPENDIX 2 149 SUMMARY 159 總結 163 SAMENVATTING 169 ACKNOWLEDGEMENTS 175 Chapter 1 General Introduction The medium (category‐2) typhoon Morakot (2009) brought 2777 mm rainfall in 72 h, causing catastrophic damage. Numerous uprooted trees and associated epiphytes were brought by floods to the coast. CHAPTER 1 General Introduction The distribution of vascular epiphytes Epiphytic plants are a characteristic component of the tropical wet forest (Benzing, 1990). In this thesis, epiphytes are defined, following Barkman (1958), as organisms that grow on plants without extracting water or nutrients from hosts’ living tissues. Unlike parasitic plants, epiphytic plants are autotrophic depending only on their hosts for anchorage whilst obtaining essential resources by intercepting dry and wet depositions (e.g. dust, litter, rainfall and fog). It is not rare to find so‐called accidental epiphytes growing on other plants; however, those are mostly unable to reproduce in the canopy (Moffett, 2000). The focus in this thesis is on vascular epiphytic plants, whereas many other organisms such as bryophytes and lichens can also be found growing as epiphytes in the forest canopy. Based on their life history, vascular epiphytes can be classified into true epiphytes (holo‐epiphytes) and hemi‐epiphytes (Schimper, 1888). The former complete their entire life cycle without contacting the forest floor, whilst individuals of the latter spend part of their life cycle as terrestrial plants. The epiphytic life‐form is a successful adaptation of plants to the forest canopy, comprising ca. 29,000 species, or approximately 10% of all vascular plants, in 83 different families and 876 genera (Gentry and Dodson, 1987a). Epiphytes are unevenly distributed over taxonomic groups and geographic locations. The epiphyte flora is concentrated in monocotyledons, especially orchids, bromeliads and aroids, and in ferns and fern‐allies (Benzing, 1990). With few exceptions, epiphytic vascular plants are mainly found in the tropical region (< 23.5° latitude). In contrast to the Neotropics, paleotropical areas lack several species‐rich epiphytic families (e.g. Bromeliaceae, Cactaceae and Marcgraviaceae) and have received less attention from botanists. Especially from Asia, epiphyte inventories are still rare (Wolf and Flamenco‐S, 2003). Whereas epiphyte richness generally decreases with latitude, numerous studies have reported a different pattern in richness along the altitudinal gradient on mountains. Apparently epiphytes (and many other organisms) achieve greatest diversity at mid‐elevations although the altitudinal position of the diversity maximum may vary among geographical areas (Wolf and Flamenco‐S, 2003; McCain, 2004; Kromer et al., 2005; Cardelus et al., 2006; Laurance et al., 2011). Some studies (e.g. Cardelus et al., 2006) suggest that the observed hump‐shape in species richness can best be explained by a null distribution (i.e. the mid‐domain effect, MDE). The MDE arises from geographic constraints on species ranges within a bounded domain (e.g. 7 INTRODUCTION from coasts to mountaintops) whereby the null model predicts that overlapping species’ ranges lead to a peak in species richness at mid‐elevation (Colwell and Lees, 2000). However, it has been argued that the MDE has been overstated in the past and that climatic factors are closely related to species richness patterns (Kessler et al., 2011). Moreover, island and continental systems seem to demonstrate different elevational diversity patterns. For instance, whereas MDE provided a reasonable explanation for bryophyte richness in the continental Andes, MDE underestimated the species richness at mid‐elevation in an Indian Ocean island (Ah‐Peng et al., 2012). The exceptional high species richness at mid‐elevation on this island reflects the presence of a large number of species with a small range size, presumably due to climatic compression. Another explanation for the unbalanced proportion of narrow‐ranged species on geologically young islands postulates that nonequilibrium communities here have a higher speciation rate owning to frequent habitat disturbance by, among others, volcanic activity, cyclones, and landslides (Whittaker, 2000). Finally, the physiological preference of different taxonomic groups probably accounts for their distinctively elevational richness along the same gradient (Krömer et al., 2013; Krömer et al., 2005; Rahbek, 1995). Epiphyte salient features Without access to a buffering supply of water and nutrients in the forest soil, the arboreal habitat for epiphytes is extremely dynamic in terms of moisture and nutrient availability. Accordingly, epiphytic plants have evolved morphologically and physiologically to deal with the typical water and nutrient‐stress conditions in the forest canopy. Bromeliads form a good example to illustrate how epiphytic plants have adapted to their arboreal habitat. Many bromeliads have developed a rosette growth form that serves as a reservoir for water and litter. Uptake is facilitated by the presence of specialized structures (trichomes) on the leaf surface. Moreover, many bromeliads possess a water‐saving metabolic pathway (Crassulacean Acid Metabolism, CAM). To reduce evapotranspiration during the day, CAM plants acquire CO2 mostly at night, and the pre‐collected CO2 is stored as an intermediate product of malic acid in special water storage tissue that permits this two‐step carbohydrate fixation process. CAM presumably evolved as an adaptation to arid conditions. CAM occurs in about 4% of the vascular flora and a majority is epiphytic plants, such as bromeliads (Martin, 1994; Winter and Smith, 1996). Interestingly, CAM plants are also found in aquatic environments, extremely wet forests or shaded understory in (sub‐)tropical