Diversity and Ecology of Vascular Epiphytes in Harenna Afromontane Forest,Bale, Ethiopia
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Date
2006-06
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Addis Ababa University
Abstract
The Ecology and Diversity of vascular epiphytes were studied in Harenna Afromontane Forest in southeastern Ethiopia at
an altitude of 2000 -3000m. Fifty-five species of vascular epiphytes (i.e.22 holoeiphytes, 3 hemiepiphytes and 30
opportunistic/humus/ epiphytes) were recorded. At all altitudinal levels, pteridophytes were the species rich group. The
Shannon-Weiner index (H/ = 1.62) of alpha diversity of the epiphyte community in the study area is low. The species
diversity of vascular epiphyte is greatly influenced by the host tree biophysical factors, such as vertical gradient of host
tree and size as well as the altitude. The regression correlation test showed that the number of species of vascular
epiphytes and the size of host tree are positively correlated (R2 = 0.34, p = 0.0001) but non-linear correlation exists
between the species number and bark and humus pH. The altitudinal distribution of species of epiphytes was higher
towards the lower altitudes (for holoepiphytes and hemiepiphytes) but humus/edaphic epiphytes don’t exhibit clear pattern
of distribution. The altitudinal distribution of epiphytes may be influenced by altitudinal factors like temperature and
moisture. The vertical distribution of vascular epiphytes (holoepiphytes and hemiepiphytes) along the vertical gradient of
the host trees indicated that most species were localized at the intermediate height, except humus epiphytes, which are
mostly restricted to the base and below first branches of the host trees. The vertical ecological gradients (i.e. solar
radiation and humidity differences from the forest floor to the canopy) may be relevant for the distribution of epiphyte
floras. Majority of the species of epiphyte occurred in a wider range of both humus and bark pH (pH = 5.0 - 6.0 for bark
and pH = 6.0 to 7.0 for humus) but few species were restricted to narrow range of pH. However, the pH values of humus
and the barks utilized by specific species of vascular epiphytes were almost corresponds to each other. The host tree
preference of vascular epiphytes was exhibited by few species such as Aerangis brachycarpa, hosted on Vernonia
amygdalina and Liparis deistelii, on Schefflera volkensii and Erythrina brucei.
Key words: Disturbance, Holoepiphyte, Hemiepiphyte, Phorophyte, and Diversity, Bark pH, Humus pH.
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Keywords
Disturbance, Holoepiphyte, Hemiepiphyte, Phorophyte, Diversity, Bark pH, Humus pH.