Effect of Eucalyptus expansion on surface runoff in the central highlands of Ethiopia
© The Author(s). 2017
Received: 2 November 2016
Accepted: 30 December 2016
Published: 27 January 2017
Land use/land cover change can affect the ecological processes of an area such as hydrological cycle. The change in the condition of water resources of an area could be a good indicator of changes in ecosystem function as a result of altered land use/land cover. Eucalyptus expansion in central Ethiopia is one of the recent land use/land cover changes causing controversy on its potential ecological effect. This study was designed to evaluate effects of three adjacent land uses/land covers, i.e. cultivated land, grassland and Eucalyptus woodlot on surface runoff in Meja River watershed, central Ethiopia.
The rainfall amount at each study catchment was collected using the rain gauge installed to record daily rainfall amount. The three land use/land cover types in each study catchment were selected for comparison as treatments. Four replications of each land use/land cover were used forming a total of 12 runoff plots. The rainfall and runoff data were collected twice a day for 91 days.
The study found that land use/land cover significantly affects surface runoff generated from the plots. Higher runoff was recorded from cultivated land. There was no significant difference on runoff volume between grassland and Eucalyptus woodlot.
This shows that expansion of Eucalyptus on grassland could not have significant impact on surface runoff generation but if planted on previously farmland could reduce surface runoff.
Sustainable land management is an important key to the increasing land productivity, better livelihoods and improved ecosystem health (Liniger et al. 2011). Factors that lead to land degradation are population pressure, overgrazing, deforestation, crop cultivation expansion on steep slope and severe soil loss in Ethiopia (Bishaw 2001; Taddese 2001; Tamene and Vlek 2008; Hurni et al. 2010; Gashaw et al. 2014). Land management is about exploring existing and possible land use/land cover (LULC) and making decision on choosing to implement the one that ensure sustainable production (UNEP 2014). Such decisions could directly affect ecosystem functions and services and alter condition of ecosystem resources such as soil, water, flora and fauna (Lemenih 2004; Maitima et al. 2009). Decision makers, therefore, need to carefully weigh the trade-off between increasing productivity on the one hand and loss of other ecosystem functions and services on the other.
In Ethiopia, land degradation had begun with the emergence of cultivation thousand years ago (Hurni 1990; Yirdaw 1996). Ethiopia is recognized for its land resource degradation, food insecurity, which has deforestation and forest degradation as its root causes (Bishaw 2001; Hurni 1990; Tamene and Vlek 2008). Various studies have shown changes in LULC, with most of the changes being the expansion of cultivated land, the increment of bare land, decline in forest areas and reduction in grazing land (Dwivedi et al. 2005; Haile et al. 2010; Kidane et al. 2012). The expansion of Eucalyptus woodlots and plantation are also observed in the highlands of Ethiopia (Jenbere et al. 2012; Chanie et al. 2013; Jaleta et al. 2016a). These dynamics in LULC have direct and indirect impact on soil and water resources of the country.
Studies have been done to assess the impact of different LULC changes on runoff and sediment yield in different parts of Ethiopia since late 1970s (Bayabil et al. 2010; Taye et al. 2013; Tebebu et al. 2015). These studies focused on effects of cultivated land, conservation areas or grassland. Results of the studies recorded the highest runoff from cultivated land (Hurni et al. 2005; Descheemaeker et al. 2006; Girmay et al. 2009; Adimassu et al. 2014).
The recent uncontrolled expansion of Eucalyptus could have significant effects on various ecosystem processes (Kebebew and Ayele 2010; Jenbere et al. 2012; Chanie et al. 2013; Tadele and Teketay 2014; Jaleta et al. 2016b). Eucalyptus expansion has been a contentious matter due to its argued ecological effects (Dessie and Erkossa 2011; Tadele and Teketay 2014; Yitaferu et al. 2013; Jaleta et al. 2016a). Various studies have assessed its effects on soil (Jenbere et al. 2012; Chanie et al. 2013; Yitaferu et al. 2013), water efficiency, allelophatic effect (Nigatu and Michelsen 1993; Fikreyesus et al. 2011) and socio-economy (Mekonnen et al. 2007; Adimassu et al. 2010; Kebebew and Ayele 2010). However, there are few studies that assessed its effect on surface runoff. Moreover, runoff-rainfall effects are site specific, due to various local effects such as climate and biophysical characteristics (Critchley et al. 1991; Girmay et al. 2009). Therefore, it is important to understand how Eucalyptus alters surface runoff patterns compared to other land use system so as to make decision on ecosystem management. The objective of this study was to evaluate surface runoff from three LULC in Meja River watershed, Oromia Regional State, central Ethiopia.
Land use is dominated by a mixed crop-livestock system. Main crops grown in the watershed are barley (Hordium vulgare), wheat (Triticum vulgare) and potato (Solanum tuberosum). The major sources of cash for the community of the area are potato and Eucalyptus products. Average family size is six people, and land holding ranges from 0 to 4 ha. Eucalyptus globulus woodlots are abundant in the study area and established mostly by replacing cultivated land and grazing lands. The soil of the area is Pellic Vertisol.
Mean of biophysical conditions of the runoff plots
Moisture content (%)
Soil temp. (°C)
Slope degree (°)
Stone cover (cm)
Ground cover (count)
(9.6 ± 1.4)a
(0.9 ± 0.1)a
26.7 ± 0.9
9.0 ± 0.6
5.6 ± 4.7
(75.5 ± 6.8)a
301.25 ± 35.8
(4.8 ± 2.5)b
(16.2 ± .2)b
(1.6 ± 0.1)b
24.9 ± 1.0
10.5 ± 0.8
(32.8 ± 2.7)b
(14.2 ± 6.3)b
(14.1 ± .2)b
(1.3 ± 0.1)a
25.5 ± 1.0
9.5 ± 0.9
14.7 ± 7.4
(86.5 ± 18.2)a
(385.0 ± 100.7)a
48.0 ± 4.1
where RC is the runoff coefficient, ∑ RoF is the total runoff depth harvested in each plot and ∑ RF is the total rainfall depth over the entire rainy season.
The significance of variance of biophysical conditions of the runoff plots, runoff coefficient and runoff volume due to the effect of land use was evaluated using analysis of the significance of variation. Genstat1 15th edition was used to analyse significance of variation. Least significant difference (LSD) test was used to compare mean value at p < 0.05. The correlation analysis was done to observe the relationship of rainfall and runoff volume for each LULC.
There is significant difference at p < 0.05 in soil moisture content among LULC types (Table 1). The moisture content in cultivated land was significantly less than the grassland and Eucalyptus woodlot. The soil electric conductivity of the grassland was significantly different at p < 0.05 with the cultivated land and Eucalyptus woodlot. The soil electric conductivity of the grassland was higher than Eucalyptus woodlot and cultivated land. There is significant difference at p < 0.05 in organic residues coverage among LULC types where Eucalyptus woodlot has significantly higher organic residues over the cultivated land and grassland.
Mean of rainfall, runoff and runoff coefficient from three LULC
Daily rainfall (mm)
Daily runoff (mm)
Runoff coefficient (%)
Total runoff (mm)
11.8 ± 0.53
(2.53 ± 0.08)a
(23.92 ± 0.33)a
(191.9 ± 4.2)a
11.8 ± 0.53
(1.95 ± 0.07)b
(17.90 ± 0.25)b
(147.8 ± 4.5)b
11.8 ± 0.53
(2.03 ± 0.07)b
(18.92 ± 0.25)b
(154.0 ± 2.9)b
Continuous ploughing of land may result in poor soil aggregate and soil crusting that reduces infiltration of rainfall. This is why cultivated land generated high runoff (Girmay et al. 2009). In addition, this study has found less soil moisture content in the cultivated land (Table 1), which directly strengthens the findings of high surface runoff from cultivated land, that means there was less rainfall infiltrate to the soil. Studies, such as Descheemaeker et al. (2006) and Girmay et al. (2009) also reported a similar finding; higher runoff from cultivated land than other land uses. However, Defersha and Melesse (2012) reported lower runoff generated from field with grown-up maize than in grassland and bare land in Kenya, which might be due to the effect of the maize crop. Conversely, Hurni et al. (2005) reported higher runoff on cultivated land than grassland and forest land in the northern highlands of Ethiopia. According to Adimassu et al. (2014), cultivated land with soil bunds generated less runoff than fallow and non-conserved cultivated land in central Ethiopia. The above listed findings could be related to the biophysical conditions of the plots together with the LULC of the plots as this study found. Applying soil and water conservation measures, therefore, reduces runoff generated especially on steep slope (Nyssen et al. 2010; Adimassu et al. 2014; Dagnew et al. 2015).
Our study found that grassland has generated least surface runoff as compared to other land uses. It is due to the dense ground coverage with grass that intercepts raindrops and reduces surface runoff to give it a time for infiltration. The moisture content in grassland was higher than other LULC, which could be one of the reasons for least surface runoff generation from the grassland. Similarly, Hurni et al. (2005) found less runoff coefficient in grassland than degraded area and cultivated land, which was similar also to the study of Girmay et al. (2009). Another study by Bayabil et al. (2010) also found a lower runoff from grassland than cultivated land with maize in Maybar watershed.
On the other hand, Eucalyptus stand generated less surface runoff compared to cultivated land. This is also due to the interception of raindrops by the stand canopy. The ground was also covered by litter fall that reduces speed of runoff and allows relatively better infiltration. This finding conforms to the findings of other studies. For instance, a study by Girmay et al. (2009) reported that in Eucalyptus-dominated plantation with limited understorey vegetation, there was no significant difference in runoff with grassland. Zhou et al. (2002) also stressed that runoff from Eucalyptus plantation decreased with accumulation of litter. However, some other studies reported result contrary to our findings. For instance, Descheemaeker et al. (2006) has found higher runoff under old Eucalyptus plantations (greater than 20 years), which was attributed to limited understorey vegetation cover.
Given the current result and other similar studies, Eucalyptus plantation could be used for catchment protection to reduce surface runoff. Its role can be enhanced with better litter accumulation and managing undergrowth. Canopy interception of Eucalyptus has made runoff generation to be less compared to the cultivated land. The intercepted water loss from Eucalyptus field is lower than other tree plantation and forests (Lima 1993). Tree planting spacing can also influence the amount of runoff generated from the field (FAO 2009). Generally, comparing runoff under Eucalyptus of different places is not advisable as other influencing factors such as soil, slope, precipitation regimes, climate, the growth stage of the forest, the use of ground vegetation and litter by local people often vary (Descheemaeker et al. 2006; FAO 2009). According to Hurni et al. (2005), surface runoff is expected to increase with land use expansion and intensification without soil and water conservation. Similar to this study, Girmay et al. (2009) and Adimassu et al. (2014) have found high correlation coefficient in the rainfall and runoff volume.
LULC can meaningfully influence runoff generation and runoff coefficient. There was significant difference in surface runoff among the compared LULC types. Cultivated land has generated higher surface runoff volume in the study period. However, there was no significant difference between grassland and Eucalyptus woodlots. This could be related with canopy cover, ground cover, litter availability or soil infiltration capacity during study period. According to the finding of this study, shifting the land use from cultivated land to Eucalyptus could reduce 21% of the surface runoff volume generated from the area. Where there is an ample amount of precipitation, using Eucalyptus as soil conservation tree could be one option. This is because it can reduce surface runoff generated from the area as compared to cultivated land.
The main reason for reduced surface runoff in Eucalyptus plantations is believed to be canopy interception that leads storage and slowly movement of water in order to percolate to the ground. As the runoff study spatially limited to the local conditions, further multiple studies should be done. Otherwise, it could not be used to compare the results from different areas. In general, the expansion of Eucalyptus has no significant impact on surface runoff generation if it is expanded on previously grassland. However, it could also significantly reduce the surface runoff generated if it is planted on previously cultivated land. In addition, this study has also observed higher soil moisture under Eucalyptus woodlots than cultivated land. Depending the above observations, Eucalyptus can be used as area conservation tree, especially to reduce soil erosion by water, where high runoff recorded fields with consideration of tree planting spacing. The effect of proper Eucalyptus planting spacing and litter accumulation level on the runoff generation needs further studies in the country.
The first author is funded by the Alliance for Green Revolution in Africa (AGRA) in Sokoine University of Agriculture for his entire PhD study. The International Foundation for Science (IFS) has supported the research work. The authors recognize the support given by the Central Ethiopia Environment and Forestry Research Center in Ethiopia and Sokoine University of Agriculture in Tanzania.
This work was carried out in collaboration between all authors. Author DJ designed the study, managed the literature searches and wrote the first draft of the manuscript. Authors BPM, HFM and ML edited and reviewed the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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