Topography-Induced Local Climatic Variations as the Decisive Factor in the Shaping of Epiphyte Distributions in Chilan, Northeastern Taiwan

To identify the determining microclimatic factors affecting epiphyte distributions, we comprehensively investigated the epiphyte community of montane cloud forests in Chilan. Four sites of adjacent old-growth forests were chosen based on the degree of prevailing wind exposure. At each site, a micrometeorological station was installed about 20 m in the forest canopy. Five emergent trees (with heights of 19~46 m and DBHs of 73~230 cm) were selected at each site for tree structure measurement and epiphyte inventory. In total, 2043 occurrences of 61 epiphytic species were recorded. Epiphytes were most abundant and diverse at the Lake site, followed by the Lee, Wind, and WindN sites. The epiphyte assemblages greatly differed across these sites, which was likely determined by the range variation in vapor pressure deficit (VPD). At least 14 site-exclusive species were identified across the four sites. This is the first study comparing epiphyte distributions of old-growth forests at a fine topographic scale. We found that small changes in microclimate, especially the range variance of VPD, dramatically affect epiphyte communities. Our results reinforce the understanding that epiphytes are a highly sensitive functional group of the forest ecosystem and serve as a good indicator of climate change.