Rare Pteridophytes are disproportionately frequent in the tropical forest of Xishuangbanna, Yunnan, China

Abstract

The richness and cover of tropical fern life-forms — terrestrial and epiphytic — vary due to their ecology and evolutionary history. It is important to understand the responses of both terrestrial and epiphytic species in relation to topography, as elevation and other aspects, to better predict their distribution. This study has investigated the richness and cover of terrestrial and epiphytic fern species in the landscape of Xishuangbanna, Yunnan, China. The ferns were classified as either rare or common based on their occurrence and the cover values from 75 transects. A General Linear Model was created to understand the impact of the elevation and topographic aspects on the rare and common fern species. A total of 130 ferns species were found. Out of the total richness, 74% of species were considered rare and assessed as having either a narrow or a wide distribution but low frequency. The rarity increased up to 90% for the epiphytic species. Both rare and common epiphytic species had higher richness and cover values at higher elevations. While common epiphytes had higher cover values at a high elevation in the northern aspect, the rare epiphyte species were richer at a higher elevation for both aspects. The richness and cover of the terrestrial species was negatively correlated with elevation and there was a significant interaction. Specifically, most of the rare and common terrestrial ferns were in the lowland sites of Xishuangbanna (from 600 m a.s.l.) However, only 20 species out of the total 130 species contributed to a total cover above 50% with the other species having only a minor density. Our results emphasize the high number of rare species with a low occurrence and show there to be a conservation concern in the fragmented tropical landscape of southern Yunnan.