The influence of tree architecture, forest remnants, and dispersal syndrome on roadside epiphyte diversity in a highly urbanized tropical environment

Abstract

Urban environments generally have reduced biodiversity, nevertheless they may contribute to biodiversity conservation. The presence of epiphytes on urban trees indicates viability of urban areas as repositories of biodiversity; however the influence of biophysical and local habitat variables on the occurrence and diversity of epiphytes on urban trees has not been studied. Epiphytes were surveyed on 1170 roadside Albizia saman trees along 39 roads in the tropical city-state of Singapore. Eighty-seven percent of trees were host to at least one epiphyte species. A total of 51 epiphyte species were encountered, 33 of which were native and represented one-third of Singapore’s 113 extant native epiphyte species. Generalized linear mixed models revealed that at the tree level, DBH, fork structure (branch multiplicity), and distance of the host tree from nearest forest patch were associated with epiphyte richness, whereas at the road level, surrounding habitat type, fork structure, and average tree height were associated with epiphyte diversity (Simpson’s reciprocal index [1/λ]). Canonical correspondence analysis showed that the presence of a species was often influenced by a single factor rather than multiple factors, e.g. distance to forest, host tree trunk diameter or height, or host tree branching complexity. This study suggests that an understanding of native epiphytes’ dispersal syndrome, the preservation of forest remnants, and protection of trees—especially large and tall trees exhibiting complex architecture—are crucial for epiphyte conservation in highly urbanized environments.