Diversity and ecological analysis of vascular epiphytes in Gera wild coffee forest, Jimma Zone of Oromia Regional State, Ethiopia
Abstract
Vascular epiphyte diversity as well as ecology of epiphytes was studied in Gera Forest in southwestern Ethiopia at altitudes between 1600 and 2400 m a.s.l. Fifty sampling plots of 30 m x 30 m (4.5 ha) were surveyed in coffee and non-coffee forest for the purpose of data collection. Out of these, sixteen plots were recorded from non-coffee forest. A total of 59 species of vascular epiphytes were recorded. Out of these, 34 (59%) were holo-epiphytes, two (4%) were hemi-epiphytes, and 22 (37%) were vascular epiphytes. The dominant families on the basis of species numbers were Orchidaceae (12 species), Aspleniaceae (8 species) and Polypodiaceae (7 species). In order to evaluate altitudinal factor limiting distribution of species, diversity of vascular epiphytes was studied along an altitudinal gradient from 1600–2400 m a.s.l. According to Shannon-Weiner biodiversity index (H′ = 3.41), the vascular epiphytic diversity was found to be high. The following host traits i.e., diameter, height and host bark textures, were analyzed to find out their relation to epiphytic distribution and abundance. A higher richness of epiphyte species occurred on rough bark (38%) followed by corky (26%), flack, (25%), and very low epiphyte species were found on smooth bark (1%). These results indicate that diameter size, bark texture of host tree, horizontal stems and branches had the greatest influence on epiphytic composition and abundance in the study area. A very high accumulation of humus and thus, the ability to hold water for long time, creates a suitable condition for seedling attachment and growth of vascular epiphytes. Host tree preference of vascular epiphytes was recorded only for Vittaria volkensii species which was hosted on Syzygium guineense trees. The result of similarity analysis indicated that Gera Forest showed the highest vascular epiphytic similarity (0.35) to Yayu Forest, and the least vascular epiphytic species overlap (0.295) with Harenna Forest.
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