Master thesis at the Institute of Ecology and Evolutionary Biology, National Taiwan University (August 2019)

https://doi.org/10.6342/NTU201903764

Author: Tsung-Yi Lin

Advisor: David Zelený

Abstract: Leaf morphological traits of angiosperm species are often related to environmental factors, revealing distinct strategies of plants adapting to different habitats. Ferns have distinct growth form and life history comparing with angiosperms, though few studies have focused on how ferns’ leaf morphological traits and growing strategies change along environmental gradients, and in Taiwan there are also few research have studied on how fern species composition change along environmental gradients based on plots survey. This study aims to understand 1) how do fern and lycophyte species composition change along environmental gradients; 2) how do the trait differences between fern species relate to their leaf growing strategies, and 3) how are the relationships of community-level fern’s leaf morphological traits and environmental factors.

Taiwan has strong elevation gradient, driving the change of many environmental factors and creating diverse habitats. To find out how does elevation and other environmental factors affect ferns and lycophytes, I established 18 20×20-m plots and 60 10×10-m plots at elevation zones between 850 and 2100 m a.s.l. in northeastern Taiwan, and recorded microclimatic, topographical, soil, light, and biotic environmental factors. Terrestrial and epiphytic fern species composition were surveyed, and leaf sample were collected and measured for a set of traits including leaf thickness, leaf area, specific leaf area, area-based chlorophyll content, leaf dry matter content, succulence, leaf total carbon and nitrogen content, 13C/12C ratio, and 15N/14N ratio. In statistical analysis, species-environment relationships were analyzed by detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA), trait-trait relationships were analyzed by Pearson’s correlation test and display by principal component analysis, response of community-level traits along environmental variables were analyzed using the RLQ and fourth-corner methods.

Overall, I found 121 fern and lycophyte species, 83 ferns have been measured and analyzed, 48 are terrestrial and 35 are epiphytic. Both terrestrial and epiphytic species composition mainly changed with elevation and temperature, while terrestrial species’ composition also changed with soil pH and slope, epiphytic species’ composition also changed with soil C:N ratio (indirectly) and site openness. In terrestrial species, Plagiogyria species had optima at mid to low temperature or more acid soil habitats; Diplazium species had optima at warm habitat; several species such as Athyrium nakanoi, Blechnum melanopus had optima at steep habitat. For epiphytic species, two nest ferns and two hemiepiphytic fern had optima at high temperature habitat; Hymenophylaceae species had optima at high soil C:N ratio habitat which dominated by large Chamaecyparis tree; two hard leaf Polypodiaceae species and two Hymenophyllum species had optima at high site openness habitat. Three growing strategies are identified for terrestrial species, including 1) acquisitive, 2) delicate conservative, and 3) resistance conservative; four strategies are identified for epiphyte: 1) acquisitive drought-deciduous, 2) intermediate, 3) xeromorphic conservative, and 4) poikilohydric. Terrestrial species’ growing strategies were mainly related to the change of LDMC to the stress of cold and low nutrient availability, epiphytic species’ strategies were mainly related to the change of succulence and LA to the drought stress and light intensity.

Key words: functional traits, community ecology, fern, epiphyte, elevation, cloud forest, monsoon forest, subtropical