Microhabitat associations of vascular epiphytes in a wet tropical forest canopy

Abstract

Summary1. In tropical forests, vascular epiphyte diversity increases with tree size, which could result from an increase in area, time for colonization or an increase in microhabitat heterogeneity within-tree crowns if vascular epiphyte species are specialized to particular microhabitats within the crown. The importance of microhabitats in structuring epiphyte communities has been hypothesized for more than 120 years but not yet confirmed. 2. We tested the importance of microhabitats in structuring epiphyte communities by examining microhabitat heterogeneity and epiphyte communities within the crowns of different-sized Virola koschnyi (Myristicaceae) emergent trees in a Costa Rican tropical wet forest. We tested the degree to which epiphyte species composition was associated with environmental conditions and resources (i.e. microhabitats) using multivariate analyses and a null model that compared the observed epiphyte assemblages amongst different-sized trees and crown zones with assemblages generated randomly. This study is the first to rigorously examine the degree of microhabitat specialization in epiphyte communities. 3. Microhabitat heterogeneity, epiphyte species richness and abundance increased with tree size. The largest trees had the highest microhabitat and epiphyte diversity and a unique inner crown microhabitat with canopy humus. The few epiphytes found on small trees were mostly bark ferns. Large trees had different epiphyte communities in different parts of the crown; the inner crown contained species not abundant in any other microhabitat (i.e. aroids, cyclanths and humus ferns), and the outer crown contained bark ferns and atmospheric bromeliads. 4. Variation in species composition amongst tree size classes was significantly related to the mean daily maximum vapour pressure deficit and tree diameter, while variation within large tree crowns was significantly related to canopy humus cover. 5. Microhabitat specialization of epiphyte species increased with tree size with 6% of species significantly associated with small trees and 57% significantly associated with large trees. Of the species present in large tree crowns, 23% were specialized to the unique inner crown microhabitat. 6. Synthesis. The increase in microhabitat heterogeneity within tree crowns as trees grow contributes to changes in epiphyte community structure, which supports decades-old hypotheses of the importance of microhabitat diversity and specialization in structuring tropical epiphyte communities.

Vascular epiphytes on Pseudobombax (Malvaceae) in rocky outcrops (inselbergs) in Brazilian Atlantic Rainforest: basis for conservation of a threatened ecosystem

“…Another important factor for the higher richness observed in PP may be that the phorophytes are larger (mean dbh 46.4 cm) than in the other areas (PL -35.8 cm dbh and PR -22.4 cm dbh). These differences agree with many reports that have shown that higher epiphyte richness is associated with large phorophytes, which normally have a longer exposure time, area available for colonization and microhabitat heterogeneity (Hernández-Rosas & Carlsen 2003;Woods et al 2014). In particular, for rocky environments, the factors that limit the establishment of plants (e.g., complete or partial absence of soil, low water retention, nutrient shortage) make the species slow-growing and longer-lived (Larson et al 2000), leading phorophytes of these ecosystems support a past flora of the original forests (e.g., vascular epiphytes) that made contact with these environmental elements.…”

“…The high species richness of epiphytes is an unusual aspect of the types of rocky vegetation such as on inselbergs, where extreme environmental factors (e.g., total or partial absence of soil and nutrients, water scarcity, and direct wind exposure) limit the establishment and longevity of larger trees that support a greater richness of epiphytes (Hernández-Rosas & Carlsen 2003;Woods et al 2014). The high richness of epiphytes on the inselbergs studied here (about 151 species on 111 phorophytes) may be related to the size and architecture of Pseudobombax sp.…”

“…(maximum of 15.3 m high and up to 120 cm DBH), influences the results, since larger phorophytes typically support more-diverse epiphytic floras (Woods et al 2014) and can accommodate a larger number of rare species.…”

Diversity and distribution of epiphytic bromeliads in a Brazilian subtropical mangrove

“…Atmospheric bromeliads, with more intermittent water supply but better photoprotection (Benzing 2000, Pierce 2007, Cach-Pérez et al 2016, predominated in the edge transect, whereas tank bromeliads, which have their own water reservoir and show lower capacity of dissipation of excess radiation (Arruda and Costa 2003, Woods et al 2015, Cach-Pérez et al 2016, were more abundant in the interior of the mangrove. In mangroves, air humidity and incident radiation near the river are greater than in the forest interior (Bonnet et al 2007).…”

Vascular epiphytes in the Grumari restinga, RJ: floristic and similarities between restingas in Eastern Brazil

“…These areas present greater availability of niches provided by forest stratification (from shrubs, treelets and trees in the understory to large trees in the upper canopy), thus offering greater heterogeneity of micro-habitats used for epiphyte colonization. The occurrence of large trees and favorable climatic factors (high humidity and mild temperatures) have been reported as the main factors related to the high diversity of epiphytes in the tropical region (Woods et al 2015;Zhao et al 2015;Ding et al 2016).…”