2.1 The study area
This study was conducted in Gerba Dima forest found in south western Ethiopia between 70 45’ to 80 10’ North latitude and 350 29 ’ to 350 50’ East longitude. The studied forest is part of the mountainous highlands west of the Great Rift Valley and is situated on undulating and dissected mountain ranges between1582m to 2285m altitudinal ranges.
Figure 1. Map of the study area
The rainfall data collected from Gore meteorological station indicated that the study area receives very high annual rainfall. The climate diagram constructed using 20 years of climate data of the nearest Gore meteorological station shows unimodal rainfall pattern with the monthly mean maximum and mean minimum temperature of the area is 27.20C and 13.3 0C, respectively. The mean annual temperature is 19.20C and with slight variation from year to year (Figure 2). The mean annual rainfall of the study area is 1854mm. The rainfall pattern exhibits low rainfall in December, January and February, steadily rising to the peak period in August. The vegetation type at the studied site is part of the moist evergreen Afromontane forest, which is characterized by one, or more closed strata of evergreen trees that may attain a height of 30 to 40 m. The characteristic emergent species that form the upper canopy includePouteria adolfi-friederici , Albizia gummifera, A. schimperiana, A. grandi bracteata, Sapium ellipticum, Ekebergia capensis, Ficus sur, Hallea rubrostipulata, Olea welwitschii, Polyscias fulva and Schefflera abyssinica .
Figure 2. Climate diagram of Gore