2.1. Description of study area
Sidama National Regional state is located in south-central Ethiopia, 275 km from the Addis Abeba (Fig. 1). This region has highland (2,500-3,700 m), midland (1500-2,300 m) and lowland (< 1500 m) agro ecologies. Total annual rainfall of highland, midland and highland are ranging from 1,600 to 2000 mm, 1,200 to 1,599 mm and 400 to 800 mm, respectively. Mean monthly temperature for highland, midland and highland are 12 to 14.5°C, 15 to 19.9°C and 20 to 24.9°C, respectively (SNRSAB 2022).
2.2. Sampling techniques
Multi-stage sampling technique was applied to select the study sites. First, one district was selected from each agro ecology purposively based on the availability of IFT and road accessibility. Accordingly, Hulla, Aletachuko, and Boricha districts in the highland, midland and lowland were selected, respectively. Then, 9 kebeles (3 from each district, the lowest administrative unit in Ethiopia) were randomly selected (Fig. 1). Then, 273 sample households were randomly selected using Yamane (1967) formula at 96% confidence level. The size of sample households from each kebele was determined in proportion of total household (Table 1).
Table 1
Sample households selected across agro ecologies in the study area
Agro ecology | District | Kebele | Total household | Sample household |
Highland | | Adola kure | 1519 | 29 |
Hulla | Gasse | 1612 | 31 |
| Chalbesa | 1667 | 31 |
| Sub Total | 4798 | 91 |
Midland | Aleta chuko | Chuko lamala | 2115 | 38 |
Guurre | 1894 | 36 |
Galma | 1733 | 33 |
Sub Total | 5671 | 107 |
Lowland | Boricha | Hariro badalicha | 1643 | 31 |
Gasara kuwe | 1225 | 23 |
Dilanole | 1103 | 21 |
| Sub Total | 3971 | 75 |
Total | | | 14400 | 273 |
2.3. Data Collection
Semi structured questionnaires were used to collect primary information on demographic characteristics, landholding, land use system, availability of IFT and livestock size. Key informants (KI) interview was conducted to obtain general information about socio economic importance and availability of IFT to farmers. Thirty-six (4 from each kebeles) KI were selected purposively based on experiences on planting IFT, use for different purposes like feeding to animals. Accordingly, elders, women and model farmers which have experience about IFT were included as KI. Secondary data were collected from regional agricultural office about location, rainfall, temperature, types of crops, livestock size and total number of household.
2.4. Indigenous fodder tree inventory
In total 60 plots (one plot per farm), 20 plots from each district, were randomly laid down and the nested quadrats (20 × 20m) were used for the inventory of fodder tree species. To locate the central position of a quadrat on the farm, ocular estimation was first used to divide the farm into ten equal parts. Then, a number was assigned to each part and the sample plot was selected using random numbers (Negash et al., 2012). All individual IFT species within the quadrats were measured and recorded (Magurran, 2004). Name of species, abundance, diameter at breast height (DBH) and total height were recorded. The tree species were identified at the site, using identification keys (Tesemma 2007), and local informants.
2.5. Data analysis
To analyze the data, SPSS and SAS Version 19.0 (SAS, 2008) software were used. Descriptive statistics were used to calculate plot frequency, relative abundance, mean DBH, height and basal area for each species. A binary logistic regression was carried out to assess the effect of gender, age, family size, land size, land use types, awareness about IFT, access to seed and seedlings and interest to plant IFT on the likelihood of having IFT in the farm. ANOVA was used for continues variable, whereas Chi-square (χ2) test was used for categorical variables to assess a statistical significance of a particular comparison. The Duncan multiple comparison tests was used for mean separation at 5% uncertainty. The statistical model used was:
Yi = µ + Ai + ei.
Where: Yi is dependent variable; µ is the overall mean; Ai is independent variables and ei is the error.
The model for Binary logistic regression was formulated as follows (O'Connell, 2006):
$$\mathbf{L}\mathbf{i}=Ln\left[\frac{Yi}{1-Yi}\right]={\alpha } + \beta 1X1+\beta 2X2+ \beta 3X3+\epsilon i$$
Where;
Dependent Variable,\(\text{Y}= Ln\left[\frac{Yi}{1-Yi}\right]=\left\{\begin{array}{c}1, if farmers having IMPFT, p\left(Y=1\right)=Yi\\ 0, otherwise, p\left(Y=0\right)=1-Yi\end{array}\right.\)
Where, α = intercept of regression; β1, β2 and β3 = the regression coefficients of the independent variables; £ = Error term
2.6. Species richness and diversity analysis
Common species diversity indices including richness (S’) and Shannon diversity (H’) of IFT in different AE were conducted. H’ was used for each plot which is widely used index for comparing diversity between various habitats (Kent and Coker, 1992). The H’ was preferred, due to its sensitivity to sample size and because it gives more weight to rare species. The H’ was calculated as:
$$H{\prime }=-{\sum }_{i=1}^{\text{s}}pi*lnpi$$
Where, H ′ = Shannon-Wiener index of species diversity; s = number of species in community; pi = proportion of total abundance represented by ith species
2.7. Stand structure
The structure of IFT in agroforestry was characterized in terms of density, basal area, frequency and importance value index (IVI) (Leul et al., 2010). The DBH and height class distribution of individual fodder species was analyzed (Kent and Coker, 1992; Mata et al, 2011).
2.8. Leaf biomass yield analysis
The leaf biomass yield of IFT was estimated by measuring stem diameter using a measuring tape. The biomass yield of each IFT was calculated using the equation developed by Petmark (1983).
LogW = 2.24 logDT-1.5; Where W was leaf DM yield in kg, DT was the diameter of the trunk (cm) at 130 cm height.