Woody Species Diversity in Oxytenanthera abyssinica Based Homestead Agroforestry Systems of Serako, Northern Ethiopia

In northern Ethiopia, establishment of exclosures and management of remnant protected natural forests to conserve and enhance forest products and services have been practiced for the past three decades. However, empirical data on the effectiveness of lowland bamboo based homestead agroforestry system in rescuing woody species diversity are lacking. The study was assessed the woody species diversity, density and composition of O. abyssinica based homestead agroforestry systems in Serako, Tselemti district. Data were collected from a total of ninety nine farms and plots with 10m*10m area, ninety from less than five year, five to ten years and greater than ten years domestication of O. abyssinica based homesteads and one exclosure with nine plots as comparison were taken. The study revealed that species density, richness and diversity were significantly higher in the exclosure than in the three homesteads (p<0.000). The study showed that a total of 48 tree species in 25 families and 24 tree species in 11 families for the homestead agroforestry systems and exclosure respectively were recorded. Following the age gradient, there was a significant difference in density, richness and diversity between greater than ten and less than five year domesticated O. abyssinica homestead agroforestry systems (p<0.000). This study confirmed that woody species diversity was higher for those households that domesticate O. abyssinica on their homesteads earlier than those households that domesticate later on their homesteads. Oxytenanthera abyssinica was not found in the exclosure, showing a distinct conscious selection for planting in the homesteads as agroforestry system. It is suggested that homestead agroforestry systems are effective for increasing biodiversity and socio-economic contributions to rural households. Keywords: Oxytenanthera abyssinica, woody species diversity, Tselemti

Response of selected indigenous dryland agroforestry tree species to salinity and implications for soil fertility management

Salt tolerant plants are known to remove excess soluble salts from the soil and thus may be used in land reclamation. We studied the responses of the trees, Balinites aegyptiaca L. (Zygophyllaceae), as well as the Fabaceae, Acacia tortilis (Forssk) Hayne, and Tamarindus indica L. to salinity. Three experiments were conducted on: germination, in the laboratory; seedling performance in a lath house; and, the impact of the tree species on soil productivity in the field in Afar regional state along the Awash river, eastern Ethiopia. Mixtures of salts, composed of chlorides and sulfates were tested at different concentrations in both germination and lath house experiments in randomized complete block designs. Seedling root collar diameter and height were measured every two weeks. Soil samples were collected from randomly selected pots to examine the effect of salinity on soil properties. The effects of trees on in situ soil productivity was studied by collecting 72 soil samples at different distances from the tree and different soil depths. The soil productivity index was calculated. The study revealed that germination percentage and rate decreased significantly with increasing salt concentrations. The effects of the three tree species on soil properties were significantly different at 12.2 dS m -1 salinity level compared to the control. A. tortilis was the least salt-sensitive. Balancing the key requirements of adequate germination and growth and the ability to reduce the salt concentration of the soil solution, B. aegyptiaca is the species with the most potential. Therefore, the study suggests to use B. aegyptiaca as agroforestry trees in the form of parkland in arid and semi-arid areas where salinity problems are prominent

Arbuscular mycorrhizal fungi improve nutrient status of Commiphora myrrha seedlings under drought

In dryland ecosystems, tree and shrub seedling establishment, growth and survival are limited by access to water and nutrients. Arbuscular mycorrhizal fungi (AMF) increase seedling establishment and survival by enhancing nutrient and water acquisition. We executed a fully-factorial greenhouse experiment to determine the interactive effect of AMF (with and without), water deficit (four levels), and soil layer (topsoil and subsoil) on the biomass, growth, nutrient concentrations, and mycorrhizal root colonization of seedlings of Commiphora myrrha, a tree species that dominates large areas of dry forest and woodland in the Horn of Africa. Mycorrhizal seedlings had higher root and shoot biomass than non-mycorrhizal seedlings. They also had higher nutrient concentrations in root and shoot. Plant biomass was higher when plants were grown in topsoil at lower soil moisture levels. Mycorrhizal responsiveness was highest at lower soil moisture. The drought response index was higher for mycorrhizal than for non-mycorrhizal plants, indicating enhanced mycorrhizal benefits at lower water supply. Seedlings grew better in topsoil than in subsoil. Mycorrhizal colonization of roots of C. myrrha seedlings was higher with lower moisture and higher in topsoil than in subsoil. The increased performance of mycorrhizal C. myrrha indicates that mycorrhization is a major component of the adaptive strategy of seedlings of this species, similar to other species in these dryland deciduous ecosystems. We conclude that for restoration purposes with this species, nursery seedlings should be mycorrhized because of their enhanced growth performance

Effects of Forest Composition and Disturbance on Arbuscular Mycorrhizae Spore Density, Arbuscular Mycorrhizae Root Colonization and Soil Carbon Stocks in a Dry Afromontane Forest in Northern Ethiopia

We investigated arbuscular mycorrhizal fungi (AMF) spore density and root colonization in three distinct dry Afromontane forest plant communities, representing differing levels of disturbance and soil properties. Soil and root samples were collected from sixty-five 50 × 50-m plots from four plant communities. We collected data for AMF spore density, AMF root colonization and soil organic carbon stocks in 0–25 and 25–50 cm soil depth ranges. AMF spore density, and root colonization differed significantly among plant communities. The least disturbed Juniperus procera–Maytenus senegalensis (Jupr-Mase) plant community, which contained high tree and shrub density, had the highest AMF spore density, root colonization and soil carbon stocks. The most disturbed Cadia purpurea–Opuntia ficus-indica (Capu-Opfi) community which contained the lowest tree and shrub density supported the lowest AMF spore density, root colonization and soil carbon stocks. There was no significant difference in spore density between the two soil depths, but AMF root colonization was significantly higher in the upper soil than in the subsoil (p < 0.001). The difference in soil properties was not uniform between plant communities. Conserving remnant dry Afromontane forests and restoring the degraded forests are critical to improve and maintain forest ecosystem functioning and sustain ecosystem services

Environmental impacts and causes of conflict in the Horn of Africa : a review

The Horn of Africa region stands out amongst the planet's territories that are most volatile and vulnerable to armed violence. Conflicts have greatly affected the region over the past 50 years. The conflicts have disrupted the lives of people as well as the environment in ways that are not fully understood. Although armed conflict has generally had a negative impact on the environment, the environmental impact of conflict within the Horn of Africa has barely been evaluated. Similarly, our understanding that climate variability as well as change could have played a role in increasing or decreasing the impacts of conflicts within the Horn of Africa is insufficient. Therefore, this paper looks at the environmental impacts of conflict in the Horn of Africa since 1970 and also the role of climate variability in increasing or decreasing the impacts of conflict. Scientific publications as well as grey literature were reviewed with the aim to understand the status of past and present conflicts in the Horn of Africa, environmental impacts of conflict and the role of climate variability in decreasing or increasing impacts of conflict. The review demonstrates that conflict has extensive negative impacts on the environment in the Horn of Africa with main causes like grievances, government behaviour and interests, resource scarcity and trans border conflict as well as internal migration and climate variability. Similarly, climate variability plays a great role in exacerbating the impacts of conflict in the region. However, further research is needed to clearly show the impact of conflict and climate variability on the environment in the Horn of Africa

Changes in total and per-capital ecosystem service value in response to land-use land-cover dynamics in north-central Ethiopia

Ecosystems provide a wide range of services crucial for human well-being and decision-making processes at various levels. This study analyzed the major land cover types of north-central Ethiopia and their impact on total and per-capita ecosystem service value (ESV). The ESV was estimated using the benefit-transfer method along the established global and local coefficient values for the periods 1973, 1986, 2001, 2016, and 2024. The findings show that agricultural lands continued to expand at a rate of 563.4 ha year−1, at the expense of forests and grasslands. As a result, the total ESV of the study area declined from $101.4 to$61.03 million and $60.08–$43.69 million, respectively. The ESV per capita was also diminished by $152.4 (37.7$257 (40.6%), respectively. However, land-cover improvement during the period 2001–2016 enhanced the total and per capita ESV in the study area. Therefore, potential future research may be required to develop a valid approach for assessing the robustness and sensitivity of value coefficients for the valuation of the ESV at the landscape level.</p

Can rangelands gain from bush encroachment? Carbon stocks of communal grazing lands invaded by Prosopis juliflora

This research article published by Elsevier Ltd., 2017Rangeland ecosystems are rapidly declining due to overgrazing and bush encroachment. Little is known about how important bush encroachment is for climate change mitigation. We estimated woody plant biomass at different Prosopis juliflora cover to quantify above- and below-ground carbon (C) stocks in Afar, northern Ethiopia. We developed allometric models to estimate aboveground biomass (agB) through destructive harvesting based on crown diameter (CrD), diameter at stump height (DSH), and tree height (H) for twenty P. juliflora and 18 Acacia senegal trees. DSH showed the best model fit in predicting above ground biomass compared to H, CrD, and the combination of those predictor parameters, respectively. Models were highly significant for all agB components. Total C stocks of the entire woody species community were about 40% higher (86 Mg C ha−1) at high than at low (50 Mg C ha−1) P. juliflora encroachment categories. We conclude that allometric models using simple dendrometric parameters are highly valuable for assessing P. juliflora biomass. While in lightly invaded areas, eradication and prevention of further spread might be possible, we propose that the high C stocks of rangelands densely invaded by P. juliflora, where eradication attempts have failed, should be considered for potential C trade measures

Land Use and Land Cover Change, and Woody Vegetation Diversity in Human Driven Landscape of Gilgel Tekeze Catchment, Northern Ethiopia

Land use and land cover (LULC) change through inappropriate agricultural practices and high human and livestock population pressure have led to severe land degradation in the Ethiopian highlands. This has led to further degradation such as biodiversity loss, deforestation, and soil erosion. The study examined woody vegetation diversity status and the impact of drivers of change across different LULC types and agroecological zones in Gilgel Tekeze catchment, northern Ethiopian highlands. LULC dynamics were assessed using GIS techniques on 1976, 1986, and 2008 satellite images. Vegetation data were collected from 135 sample plots (20 m × 20 m) from five LULC types, namely, forest, shrub-bush, grazing, settlement, and cultivated land, in the three agroecological zones; Kolla, Weyna-Dega, and Dega. Differences in vegetation structure and composition and their relationship to agroecological zones were tested using two-way ANOVA and PCA technique. The results show that vegetation structure and composition significantly differed across all LULC types in different agroecological zones particularly in sapling density, tree height, and shrub height and in each agroecological zone between forest land, shrub-bush land, and settlement area. Overall, Weyna-Dega agroecological zone and the shrub-bush land had more structural and compositional diversity than the other agroecological zones and LULC types

Arbuscular mycorrhiza effects on Faidherbia albida (Del.) A. Chev. growth under varying soil water and phosphorus levels in Northern Ethiopia

Tree seedling establishment, survival and growth in dryland areas is greatly impacted by water, land use effects and soil nutrient availability. Arbuscular mycorrhizal fungi (AMF) can have a substantial effect on water and nutrient uptake by seedlings and are affected by nutrient application, water availability and inoculum source. In this study, we examined the effect of AMF inoculation, phosphorus application levels, soil water status, and inoculum source on the growth of Faidherbia albida seedlings. Two greenhouse experiments were conducted on F. albida seedlings: to compare (a) ±AMF inoculation, at three levels of volumetric soil water content (field capacity (FC), 60% of FC and 20% of FC), and three AMF inoculum sources (derived from cultivated land, grazing land and area exclosure); (b) ±AMF inoculation, at four levels of phosphorus application (0, 25, 50 and 100 mg kg−1) and three AMF inoculum sources. Inoculation with AMF, higher soil water and higher P application significantly increased the growth of seedlings (P < 0.05). F. albida seedlings responded positively to increased water levels. The highest growth and AMF colonization of seedlings was recorded under the lowest water stress with AMF inoculum from area exclosure followed by grazing land inoculum source. The lowest growth was recorded under the highest water stress and cultivated land inoculum source. Plant growth and biomass were positively correlated with increased soil P application, however, AMF colonization decreased with increasing P application. Applying P and inoculating F. albida seedlings with indigenous AMF under low water stress enables optimum plant growth improvement in dryland farming systems

Traditional gold mining in the highlands of Ethiopia: Its effect on soil loss and possible reclamation measures

Traditional gold mining (TGM) is among the off-farm income sources of smallholder communities in the highlands of Ethiopia. However, information on their impact on land degradation, taking soil loss as a key indicator, was scant. Hence, this study aimed at i) analyzing local communities’ attitudes toward TGM practice, ii) TGM impact on soil loss, and iii) possible restoration measures for the degraded gold-mined landscapes. For the evaluation of community perceptions, 96 beneficiaries were selected from three gold mining sites following stratified random sampling techniques. Soil loss measurement was done through measurement of i) the mass of soil excavated and transported to the river (TR) from 96 individuals and ii) soil volume excavated in 45 excavated soil pits (EP). Descriptive statistics and one-way ANOVA were used to analyze soil loss data, while community perception was analyzed qualitatively. The survey results indicated that the average soil loss from TR and EP were 6,075.97±8.9 t ha-1 yr-1 and 32,549.99±753.68 t ha-1, respectively. The magnitude of soil loss also showed a significant (p<0.001) difference among the three sites. Due to a lack of awareness and hiding the reality, most of the gold miners believe that TGM practice has no negative impact on the soil resource, and no post-mined reclamation strategy is implemented. It can be concluded that the existing TGM practices are not done in an environmentally friendly approach and result in adverse soil loss. Hence, stabilizing the topography of the mined sites via backfilling of mined pits and topsoil conservation and amendment measures can be suggested