Fate of Epiphytes on Phorophytes with Different Architectural Characteristics Along the Perturbation Gradient of Sabal Mexicana Forests in Veracruz, Mexico
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Journal of Vegetation Science ]]: 1–10, 2009 & 2009 International Association for Vegetation Science Fate of epiphytes on phorophytes with different architectural characteristics along the perturbation gradient of Sabal mexicana forests in Veracruz, Mexico Aguirre, A.1,2; Guevara, R.1,3,4Ã; Garcı´a, M.5,6 &Lo´pez, J.C.7,8 1Instituto de Ecologı´a, A.C. Departamento de Biologı´a Evolutiva, Apartado Postal 63, Xalapa, Veracruz 91000, Me´xico; 2E-mail: [email protected]; 3E-mail: [email protected]; 4Current address: Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA 94305, USA; 5Universidad Michoacana de San Nicola´sde Hidalgo, Facultad de Biologı´a, Ciudad Universitaria, Morelia, Michoaca´n, Me´xico; 6E-mail: [email protected]; 7Centro de Investigaciones Tropicales, Universidad Veracruzana; 8E-mail: [email protected]; ÃCorresponding author; E-mail [email protected] Abstract Keywords: Beta diversity; Epiphytic ferns; Forest frag- mentation; Ophioglossum palmatum; Phylogenetic Question: Vascular epiphytes and hemiepiphytes (E/HE) diversity. in neotropical forests account for a large fraction of plant richness, but little is known of how the interplay between Nomenclature: Hietz & Hietz-Seifert (1995a). phorophyte architectural characteristics and habitat per- turbation affect communities of E/HE. Location: Sabal mexicana forests in a coastal area of Introduction Veracruz, Mexico. Water and nutrient uptake limits plant growth Methods: We compared communities of E/HE on phor- in most epiphytic environments (Benzing 1987, ophytes with different architectural characteristics – the 1990; Hietz & Briones 1998; Holbrook & Putz 1996). palm S. mexicana and non-palm phorophytes – in three Nonetheless, epiphytes/hemi-epiphytes (E/HE) ac- environments: conserved sites, perturbed sites and small count for ca. 10% of the vascular flora in the world regenerated forest fragments. We combined traditional (Gentry & Dodson, 1987). E/HE harbour a great (abundance, species richness, similarity and complemen- diversity of arthropods (Ellwood & Foster, 2004), tarity indices) and more recent (phylogenetic diversity) metrics to describe the communities of E/HE. provide abundant resources for frugivores and pol- linators (Cruz-Ango´n & Greenberg, 2005; Gentry & Dodson, 1987), and take part in other important Results: Overall, we recorded 924 E/HE individuals (nine families, 16 genera and 21 species). The abundance and ecosystem processes, such as nitrogen fixation species richness of E/HE was higher on palms than on (Puente & Bashan, 1994). non-palm phorophytes. Abundance-based complementa- Microenvironmental conditions in epiphytic rities between phorophytes and sites were high. We rooting substrates are mediated not only by local- detected clear changes in community structure of E/HE scale environmental conditions but also by the ar- with habitat perturbation, but there were no effects on the chitectural characteristics of the phorophyte phylogenetic diversity of the E/HE community. Palm (Nadkarni 1984, 2002; Holbrook & Putz 1996). The phorophytes hosted a more phylogenetically diverse com- architectural characteristics of many species of munity of E/HE than did non-palm phorophytes. palms in the genera Caryota, Copernicia, Phoenix, Rhaphis, Sabal, Syagrus, Trachycarpus and Wa- Conclusions: Palm phorophytes are key elements support- shingtonia provide environments hospitable to ing the conservation of resilient communities of E/HE in epiphytes (Davis 1970; Putz & Holbrook 1989; S. mexicana forest. Habitat fragmentation has a strong effect on the structure of the E/HE community in S. Lawton & Williams-Linera 1996; Lo´pez & Dirzo mexicana forests. Ferns are the group of epiphytes most 2007). These palms retain their old leaf bases on the severely affected by habitat perturbation, but we detected trunk, creating a textured crisscross pattern, the in- no significant effect on the phylogenetic diversity of the ner part of which is protected from direct solar community. radiation and retains humidity. This thus facilitates 2 Aguirre, A. et al. the growth of decomposing microbes and detrivor- ing different architectural characteristics for the ous arthropods that break down and mix organic conservation of E/HE. matter with airborne dust, creating a fertile sub- Here, we investigated the effects of S. mexicana strate for epiphytes (Guevara & Lo´pez 2007). Lo´pez forest conversion on a community of vascular epi- (2007) estimated that a single palm of Sabal mex- phytes, considering two important components icana in central Veracruz contained up to 9 kg of relevant to the conservation of epiphytes. First, we fertile epiphytic soil, with 40-times more carbon, 14- considered two types of phorophyte with distinct ar- times more nitrogen and 12-times more phosphorus chitectures: S. mexicana palms and non-palm trees. than the soil supporting the growth of the palm. In Second, because the effects of forest conversion can contrast, in most non-palm trees, the epiphytic sub- vary among different groups of epiphytes, we ana- strate is often reduced to a layer of aerial roots of the lysed whether phylogenetic diversity of the epiphyte epiphytes, which trap airborne nutrients (Nadkarni community was affected by forest conversion and 1984; Nadkarni et al. 2002). type of phorophyte in this forest. We aimed to an- S. mexicana grows in lowlands on the Atlantic swer three questions. (1) Do sympatric phorophytes and Pacific coasts of Mexico, and is commonly as- with different trunk architectures host similar com- sociated with heavily transformed tropical forests munities of E/HE? (2) Is there a phylogenetic bias for (Zona 1990). However, in central Veracruz, S. mex- the composition of vascular epiphytes on different icana is a dominant species in remnants of primary types of phorophyte? (3) What are the effects of for- forests, a rare and endangered vegetation type in est conversion on the communities of vascular Mexico (Lo´pez & Dirzo 2007). Forests dominated epiphytes on the two types of phorophyte? by palms with textured crisscross trunks are scat- tered widely throughout the Americas: S. palmetto forests in southern Florida (Wade & Langdon Methods 1990), S. mexicana forests in central Veracruz, Mexico (Lo´pez & Dirzo 2007), Orbignya cohune Study site forests in Belize and other parts of Central America (Wright et al. 1959), and Copernicia tectorum in the The study was conducted in S. mexicana forests Venezuelan Llanos (Mayer 1933; Putz & Holbrook (1814804000-1815105100N, 9610502000-9610102500W), an 1989). In these forests, palms are accompanied by a ecosystem whose distribution in Mexico is restricted host of other tree species. For instance, Lo´pez & to the central coastal area of Veracruz (Pennington Dirzo (2007) listed 64 tree species in S. mexicana & Sarukha´n 1998; Lo´pez & Dirzo 2007), although forests, including Brosimum alicastrum, Coccoloba similar formations occur in southern Florida (Wade barbadensis, Pithecellobium dulce, Nectandra salici- & Langdon 1990), Belize, other parts of Central folia, Ocotea cernua and Malvaviscus arboreus. America (Wright et al. 1959) and in the Venezuelan These palm-dominated forests offer a good oppor- Llanos (Mayer 1933; Putz & Holbrook 1989). tunity to investigate the fates of communities of The floristic richness of the S. mexicana forests is epiphytes on phorophytes having different archi- around 81 species, including trees and epiphytes, tectural characteristics and following human and has a clear affinity with the tropical dry and disturbance. tropical wet forests of Mexico, with a small re- S. mexicana forests are heavily impacted by hu- presentation of taxa from arid ecosystems (Lo´pez & man activities and have been predominantly Dirzo 2007). converted to pastures (Lo´pez & Dirzo 2007). Var- Most of the S. mexicana forests have been con- ious studies have documented the negative effects of verted to pastures and are systematically subjected natural forest conversion on the diversity of com- to dry season fires, preventing the establishment of munities of epiphytes (Hietz-Seifert et al. 1996; plants other than Sabal palms and C. barbadensis Padmawathe et al. 2004; Cascante-Marı´n et al. 2006; trees. Some landowners stopped the practice of an- Flores-Palacios & Garcı´a-Franco 2008). Further, nually burning the pastures more than 40 year ago, some studies have also shown that forest conversion and vegetation patches have re-grown, nourished by has different effects on different groups of epi- S. mexicana palms, but are still kept in check by phytes. For instance, in a moist lowland forest in cattle grazing (local peasants, personal communica- India, the abundance of vascular epiphytes, but not tion). The vegetation patches range in diameter of orchids, was negatively affected by selective log- from 2 to 30 m, and host a large fraction of the flora ging (Padmawathe et al. 2004). However, we know found in the conserved forest sites (Herna´ndez-Her- very little about the relevance of phorophytes hav- na´ndez 2009). - Fate of epiphytes on phorophytes with different architectural characteristics - 3 Sampling design gram based on published works on their phylo- genetic relationships (Pryer et al. 2004). Then, fol- In this study, we analysed the diversity of E/HE lowing the Missouri Botanical Garden phylogenetic communities in three different environments: con- tree service for vascular plants, we counted the served forest sites, perturbed sites (managed number of nodes to a common