Abstract:
Agroforestry is accompanies different diversity of plants and has a unique capacity of balancing
the net carbon emissions as a sink and reservoir for carbon dioxide at both above and belowgrou
nd. The objective of this study was to investigate woody species diversity and carbon stock in
coffee-based homegarden agroforestry in the Dellomenna District of Bale Zone, Ethiopia. Three
study kebeles (Wabaro, Erba and, Chiri) were selected purposively. In each selected kebele, two
sites were identified and selected randomly. Within sites systematic sampling techniques were
employed to select the homegardens and laid down plots. Hence, forty-eight sample plots each
having an area of 10 *10 m was laid for trees and shrubs with a height of >1.5 m and DBH
>2.5cm.Within major plots five subplots of 2*2 m, at four corners and in the center, were laid
for seedling /saplings having height > 0.50 m and less than 1.5 m or with D40 cm or DBH <2.5
cm including the seedlings with a height of <0.50 m. Therefore, the diameter and heights were
measured by using diameter tape and hypsometer respectively. Trees, saplings and seedlings
encountered in the plots were recorded and identified using the standard procedure. Soil
samples from four corners and at the center were taken by pressing an auger to a depth of 30 cm
. Hence, 48 composite soil samples were used for organic carbon determination. Undisturbed soi
l bulk density was collected by using a 6.2 cm length and 5 cm diameter core sampler for this pur
pose 48 soil samples were used. AGB of individual trees and coffee was estimated using allometr
ic equation of AGB (tree) = 0.091 * d
2.472 and AGB (coffee) = 0.147*d2
40 cm respectively. Then
means exhibited significance difference was tested by LSD at p<0.05 using Genstat18th edition
(software). The diversity of woody species was analyzed by using diversity indices. A total of 39
woody species representing 24 families were recorded. Out of the total woody species
encountered in the 48 quadrats, 71.9 % were trees and shrubs, 28.1 % was seedlings and
saplings. Shannon diversity and evenness at kebele level were ranged from 1.68 - 2.5 and 0.64 -
0.79 respectively. The mean Shannon diversity and evenness at plot level and structural
parameters show significant variation at p<0.05. Almost 96.07% of the variation of the carbon
stock of woody species in coffee based homegarden agroforestry was due to diameter variation
and the remaining 3.93% variation was due to other unexplained factors. The overall mean of
each carbon pool in the coffee based homegarden agroforestry was 48.63,9.73 and, 111.2ton
ha 1
for AGBC, BGBC and, SOC respectively.The total mean carbon stock for biomass and SOC
stock were 175.1 and 333.5 ton per hectare respectively. Generally the study indicates that coffe
e-based homegarden agroforestry could be one option to combat the problems of climate change
through reducing the carbon emission. However, coffee-based homegarden agroforestry of the
area is dominated by a fruit trees and this result in low species diversity decline in the frequency
of some indigenous woody species, leading to a loss in carbon stock and species diversity.