Edge effect on epiphyllous bryophytes in Taita Hills fragmented afromontane forests

摘要

We investigated forest edge effects on the composition, abundance and species richness of epiphyllous (leaf-inhabiting) bryophytes in tropical cloud-forest fragments in the Taita Hills (Eastern Arc Mountains, Kenya). Six sample plots each of 0.04 ha (20 x 20 m) were established along a disturbance gradient extending in 200 m from the forest edge at three sites. Four leaves were collected from each phorophyte species and the diversity of epiphyllous bryophytes examined. Relative humidity and temperature readings were recorded using time-calibrated data loggers and a digital hygrometer. The epiphyllous species composition among localities and forest-edge distance classes were analysed using multivariate procedures. Overall, 1387 leaves distributed across 489 phorophytes were studied, and 95 species of bryophyte epiphylls were found in the 18 0.04-ha plots selected. The richness and distribution of epiphyllous bryophyte species did not change with the forest-edge distance, but rather depended on phorophyte species composition and (micro-) environmental variables such as sunlight exposure and spatial and dimensional canopy structure. The differences in epiphyll diversity among forest fragments were thus influenced by site-specific characteristics. Our findings suggest that management policies addressed to preserve ancient uncut stands that exhibit as much original phorophyte diversity as possible, need to be urgently achieved to protect epiphyll communities in African tropical cloud forests.