UvA-DARE (Digital Academic Repository) A protocol for sampling vascular epiphyte richness and abundance Wolf, J.H.D.; Gradstein, S.R.; Nadkarni, N.M. DOI 10.1017/S0266467408005786 Publication date 2009 Document Version Final published version Published in Journal of Tropical Ecology Link to publication Citation for published version (APA): Wolf, J. H. D., Gradstein, S. R., & Nadkarni, N. M. (2009). A protocol for sampling vascular epiphyte richness and abundance. Journal of Tropical Ecology, 25(2), 107-121. https://doi.org/10.1017/S0266467408005786 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). 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Nadkarni‡ ∗ Institute for Biodiversity and Ecosystem Dynamics (IBED), Universiteit van Amsterdam, Kruislaan 318, NL-1098 SM Amsterdam, the Netherlands † Institute of Plant Sciences, University of Gottingen,¨ Untere Karspule¨ 2, 37073 Gottingen,¨ Germany ‡ The Evergreen State College, Olympia, Washington 98505, USA (Accepted 6 December 2008) Abstract: The sampling of epiphytes is fraught with methodological difficulties. We present a protocol to sample and analyse vascular epiphyte richness and abundance in forests of different structure (SVERA). Epiphyte abundance is estimated as biomass by recording the number of plant components in a range of size cohorts. Epiphyte species biomass is estimated on 35 sample-trees, evenly distributed over six trunk diameter-size cohorts (10 trees with dbh > 30 cm). Tree height, dbh and number of forks (diameter > 5 cm) yield a dimensionless estimate of the size of the tree. Epiphyte dry weight and species richness between forests is compared with ANCOVA that controls for tree size. SChao1 is used as an estimate of the total number of species at the sites. The relative dependence of the distribution of the epiphyte communities on environmental and spatial variables may be assessed using multivariate analysis and Mantel test. In a case study, we compared epiphyte vegetation of six Mexican oak forests and one Colombian oak forest at similar elevation. We found a strongly significant positive correlation between tree size and epiphyte richness or biomass at all sites. In forests with a higher diversity of host trees, more trees must be sampled. Epiphyte biomass at the Colombian site was lower than in any of the Mexican sites; without correction for tree size no significant differences in terms of epiphyte biomass could be detected. The occurrence of spatial dependence, at both the landscape level and at the tree level, shows that the inclusion of spatial descriptors in SVERA is justified. Key Words: autocorrelation, bromeliads, Colombia, community ecology, Mexico, multivariate analysis, oak forest, species diversity INTRODUCTION Parker 1994, Parker et al. 1992, Perry 1978, Whiteacre 1981). In contrast, quantitative methods to sample and In his classic study on the sociology of epiphytes, Went analyse vascular epiphyte vegetation in the canopy have (1940) described the canopy by lying, face-up, with field received little attention, with a few exceptions (Barker glasses on a stretcher, while field-assistants transcribed & Pinard 2001, Bergstrom & Tweedie 1998, Gradstein his spoken observations. Plants fallen to the ground et al. 1996, 2003; ter Steege & Cornelissen 1988). and local tree-climbers provided voucher collections. Comparisons among inventories and datasets are often Although these techniques seem primitive compared with hampered because investigators used different sample those used by modern canopy scientists, much of our units (e.g. branch segments, branches, trees, ground knowledge of epiphyte distribution is still based on this surface plots) or sample sizes (e.g. number of trees, type of data (Johansson 1974, Ochsner 1935, Schimper number and size of plots) (Wolf & Flamenco-S. 2003). 1888, van Oye 1924). Ideally, comparisons should be performed on trees of the The innovation of rope-climbing and other canopy- same species and of the same size (Johansson 1974). access techniques such as walkways, platforms, cranes Such situations, however, are difficult to find in multiple and hot-air balloons to gain access to the forest canopy localities in species-rich tropical forests. Our objective resulted in a burgeoning of interest in canopy research in this paper is to develop a universal, quantitatively (Dial & Tobin 1994, Gottsberger & Doring¨ 1995, Laman rigorous sample design that permits comparisons of 1995, Mitchell et al. 2002, Moffett 1993, Nadkarni & epiphyte richness and abundance among forest stands of differing structure. We recognize three reasons for the lack of universal 1Corresponding author. Email: [email protected] sampling protocols for epiphytes. First, epiphytes grow 108 JANH.D.WOLFET AL. in an intricately structured three-dimensional habitat and Abundance (SVERA). SVERA compares the richness within which discrete branches are patchily distributed. and abundance of epiphytes in forest stands that differ Even within the same tree, two branch segments differ in structure (as a result, for example, from disturbance). with respect to their history, topology and microclimate. SVERA adds three critical activities to the RRED-protocol. Second, epiphyte communities are very rich in species, First, SVERA estimates the true abundance of each particularly in wet tropical areas, so minimal areas species, in terms of species biomass. Although per cent (defined as the area that contains an adequate sample branch cover provides a good estimate of biomass for of species of regular occurrence; Westhoff & van der non-vascular epiphytes (McCune 1990), it is not a good Maarel 1973) can exceed the surface area of individual measure for vascular ones because many species extend branches or even whole trees (Johansson 1974, Wolf beyond the branch surface area. Using the number of 1993a, b). Third, the distribution of epiphytes is non- individuals is also suspect because large plants use more random (Laube & Zotz 2006), being heterogeneous at resources than small ones (Benavides et al. 2005, Zotz a range of spatial and temporal scales (Bennett 1986, 2007a, b). Distinguishing true individuals (genets) in a Nieder et al. 2000, Wolf 1994, 2005). Nearby trees may mass of ramets is also difficult, especially in montane have more similar epiphyte vegetation than those far forests. Rare species that occur only once or twice, away (Bader et al. 2000, Barkman 1958, Cascante-Mar´ın however, may be counted with confidence because the et al. 2006, Catling et al. 1986, Hietz & Hietz-Seifert 1995, number of occurrences is likely the same as the number Madison 1979). of individuals. SVERA uses the number of individuals in For epiphytes in humid tropical forests, the rare species to estimate total number of species in the combination of high richness (α-diversity) and high inventories (SChao). In lowland forests, spatially separated species turnover (β-diversity) causes the number of stands of epiphytes have been counted (Sanford 1968) species and their densities to rise continuously with instead of individuals, but this ignores the fact that increasing sample area (Annaselvam & Parthasarathy epiphytes can have hidden connections within canopy 2001). In most epiphyte community studies, sample plots soil or on undersides of branches. Estimating biomass may have been 0.1 to 1 ha, which comprise only a portion of overcome the problem of counting individuals but is more the local epiphyte flora. For example, in a 170-ha study time-consuming. Destructive sampling can incur long- area in Ecuador, Gentry & Dodson (1987a, b) found 127 term damage (Muir et al. 2006). Nevertheless, dry weight out of 227 vascular epiphyte species in a 0.1-ha plot. from recorded plant sizes in a number of size-cohorts On relatively small Annona trees, Nieder & Zotz (1998) provides meaningful results (Benavides et al. 2006, Wolf concludedthat30treesmustbesampledtoinclude 2005). the 10 most abundant species with 50% certainty. If Second, SVERA incorporates tree basal area, tree the same holds for large trees, a substantial sampling density and trunk diameter frequency distributions so effort is needed. This problem may be handled by using that epiphyte abundance data can be extrapolated to a relatively scale-independent diversity measure such as a forest area. The diameter frequency distribution can parametric Fisher’s alpha (Magurran 1988). However, reveal the history and conservation status of the forest, alpha