The study area
This study occurred in Oromia National Regional State’s newly
established Arjo Diga Forest, East Wollega Zone. In 2014, the UNDP, the
Federal Government, and regional governments developed a conservation
program in this area. The size of the forest is 1268.6 hectares, with an
elevation range of 1200 to 2220 meters above sea level. It is roughly
346 kilometers west of Addis Ababa and 15 kilometers west of Nekemte
town. It lies between the longitudes of 8o56’00”N and
9o10’00”N, and 36o15’30”E and
36o26’30”E. (Fig. 1). The area’s temporal rainfall
pattern indicates a single peak around July and August, with no
discernible difference between the lesser and main rain seasons, as is
common in several parts of Ethiopia. The area’s average annual rainfall
ranges from 800mm to 2110mm, with a monomial rainfall distribution
marked by high amounts of rainfall over a lengthy period of time during
the summer. May through October is the rainy season, with the highest
average monthly rainfall in July, June, and August (NMA, 2017). The
lowest temperatures ranged from 12 to 18 degrees Celsius during wet,
while the maximum temperatures ranged from25 to 35 degrees Celsius
during the dry season.