The Effect of Rain Forest Canopy Architecture on the Distribution of Epiphytic Ferns (Asplenium spp.) in Sabah, Malaysia Tom M. Fayle 1,5 , Arthur Y. C. Chung 2 , Alex J. Dumbrell 3 , Paul Eggleton 4 , and William A. Foster 1 1 Insect Ecology Group, University Museum of Zoology Cambridge, Downing Street, Cambridge CB2 3EJ, UK 2 Forest Research Centre, Forestry Department, PO Box 1407, 90715 Sandakan, Sabah, Malaysia 3 Department of Biology, University of York, PO Box 373, York YO10 5YW, UK 4 Department of Entomology, Natural History Museum, Cromwell Road, London SW6 5BD, UK ABSTRACT Epiphytic plants are a dominant component of the rain forest canopy biota. They represent a significant proportion of canopy plant biomass and diversity, play a key role in nutrient cycling, and support highly abundant and diverse animal communities. Understanding the factors affecting their distribution in this three-dimensional habitat is consequently of great importance, not least because they may be particularly vulnerable to climate change and habitat conversion. Here we investigate how canopy architecture affects the distribution of two species of bird’s nest fern (Asplenium spp.) in pristine rain forest. Both species were found at high abundances (Asplenium phyllitidis: 136/ha, SE Æ 31.6, Asplenium nidus: 44/ha, SE Æ 9.2) and their distributions were differentially affected by canopy architecture. Asplenium phyllitidis was found only at heights o 30 m in areas with a thicker lower canopy layer. Asplenium nidus was found at all heights in the canopy and was associated with emergent trees and areas with an open understory. Larger A. phyllitidis were found higher in the canopy while larger A. nidus were found on trunks and branches with a wider diameter. Asplenium nidus seems adapted to withstand the hot dry conditions in the upper canopy and in gaps, and its size is consequently limited only by the size of its support. Asplenium phyllitidis is dominant in areas that are cooler and damper, and so the growth rate of individuals may be limited by light levels. We discuss possible implications of this partitioning for epiphyte communities in the face of climate change and habitat conversion. Abstract in Malay is available at http://www.blackwell-synergy.com/loi/btp Key words: Asplenium nidus; Asplenium phyllitidis; bird’s nest fern; climate change; habitat conversion; microclimate; vertical stratification. EPIPHYTIC PLANTS ARE A MAJOR CONTRIBUTOR to vascular plant diver- sity (Hsu et al. 2002) and biomass (Tanner 1980, Nadkarni 1984) in the canopies of many tropical forests. They contain a high pro- portion of the canopy nutrient capital (Nadkarni 1984) and can support diverse communities of animals (Ellwood et al. 2002, Ellwood & Foster 2004). They are also ideal for use as microcosms for investigating questions in community ecology (e.g., Richardson 1999). Understanding how epiphyte species partition the heteroge- neous canopy environment is therefore of great importance. One of the most abundant epiphytic plants in the old-world tro- pics is the bird’s nest fern (Asplenium spp.; Fig. S1). Their range extends from the east coast of Africa through India and SE Asia to Japan, north- ern Australia and many islands in the western Pacific (Holttum 1976), and they are found both in primary forest and in human-modified hab- itats, such as logged forest and oil palm plantations (Turner 2005). Bird’s nest ferns play an important role in the ecology of old- world tropical forest canopies. They are litter-basket epiphytes, in- tercepting falling leaf litter and using the nutrients resulting from the decomposition of these leaves. One consequence of this is an increase in nutrient content of stemflow water passing through the ferns (Turner et al. 2007), which may have an effect on the plant and animal communities living below them. They also intercept and store water in their sponge-like root mass and consequently buffer local microclimate in the canopy (Turner & Foster 2006). As a result they provide an important refuge for animals ranging from ar- thropods to bats, away from the hot dry conditions found elsewhere in the canopy (Hodgkison et al. 2003, Ellwood & Foster 2004). They are often found growing in mats with many other species of epiphyte (T. M. Fayle, pers. obs.), presumably because their nutrient-rich cores provide an ideal site for germination. Therefore these ferns are of great importance in the ecology of other canopy plants and animals, and deducing which factors affect their distribution is an important step toward understanding the workings of the rain forest ecosystem. Microclimate may be of particular importance in determining the distribution of bird’s nest ferns. In the canopy temperature and humidity vary a great deal, mainly as a consequence of differences in canopy architecture (Dial et al. 2006). Despite the fact that bird’s nest ferns can absorb and store water they are still susceptible to drought (Freiberg & Turton 2007). The microclimate in an area will therefore affect the probability of fern mortality and conse- quently will affect the distribution of different species. This is of particular concern because the close ecological ties between epiphytes and microclimate may make them susceptible to climate change (Mondragon et al. 2004) and habitat conversion (Pad- mawathe et al. 2004). Mean global temperature is predicted to increase by 1.8–41C by 2090–2099 compared with 1980–1999 (IPCC 2007) and this will presumably cause higher rates of Received 26 November 2008; revision accepted 23 January 2009. 5 Corresponding author; e-mail: tmf26@cam.ac.uk BIOTROPICA 41(6): 676–681 2009 10.1111/j.1744-7429.2009.00523.x 676 r 2009 The Author(s) Journal compilation r 2009 by The Association for Tropical Biology and Conservation