Parkland trees on smallholder farms ameliorate soil physical-chemical properties in the semi-arid area of Tigray,Ethiopia

Proposed agroforestry options should begin with the species that farmers are most familiar with,which would be the native multipurpose trees that have evolved under smallholder farms and socioeconomic conditions.The African birch(Anogeissus leiocarpa(DC.)Guill.&Perr.)and pink jacaranda(Stereospermum kunthianum Cham.)trees are the dominant species in the agroforestry parkland system in the drylands of Tigray,Ethiopia.Smallholder farmers highly value these trees for their multifunctional uses including timber,firewood,charcoal,medicine,etc.These trees also could improve soil fertility.However,the amount of soil physical and chemical properties enhanced by the two species must be determined to maintain the sustainable conservation of the species in the parklands and to scale up to similar agroecological systems.Hence,we selected twelve isolated trees,six from each species that had similar dendrometric characteristics and were growing in similar environmental conditions.We divided the canopy cover of each tree into three radial distances:mid-canopy,canopy edge,and canopy gap(control).At each distance,we took soil samples from three different depths.We collected 216 soil samples(half disturbed and the other half undisturbed)from each canopy position and soil depth.Bulk density(BD),soil moisture content(SMC),soil organic carbon(SOC),total nitrogen(TN),available phosphorus(AP),available potassium(AK),p H,electrical conductivity(EC),and cation exchange capacity(CEC)were analysed.Results revealed that soil physical and chemical properties significantly improved except for soil texture and EC under both species,CEC under A.leiocarpus,and soil p H under S.kunthianum,all the studied soils were improved under both species canopy as compared with canopy gap.SMC,TN,AP,and AK under canopy of these trees were respectively 24.1%,11.1%,55.0%,and 9.3% higher than those soils under control.The two parkland agroforestry species significantly enhanced soil fertility near the canopy of topsoil through improving soil physical and chemical properties.These two species were recommended in the drylands with similar agro-ecological systems.

Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest, northern Ethiopia

Arbuscular mycorrhiza fungi(AMF) are vital in the regeneration of vegetation in disturbed ecosystems due to their numerous ecological advantages and therefore are good indicators of soil and ecosystem health at large. This study was aimed at determining how the seasonal, vegetation cover density, edaphic and anthropogenic factors affect AMF root colonization(RC) and spore density(SD)in Desa’a dry Afromontane forest. AMF RC and SD in the rhizosphere of five dominant woody species, Juniperus procera, Olea europaea, Maytenus arbutifolia, Carissa spinarum and Dodonaea angustifolia growing in Desa’a forest were studied during the rainy and the dry seasons in three permanent study vegetation cover density plots(dense, medium, and poor). Each plot(160 x40 m2) has two management practices(fenced and unfenced plots) of area. A 100 g sample of rhizosphere soil from moisturefree composite soil was used to determine spore density.Spore density ranged from 50 to 4467 spores/100 g soil,and all species were colonized by AMF within a range of 4–95%. Glomus was the dominant genus in the rhizosphere of all species. Vegetation cover density strongly affected SD and RC. The SD was significantly higher(p < 0.05) in the poor vegetation cover density than in the other two and lowest in the dense cover; root colonization showed the reverse trend. Management practices significantly(p <0.05) influenced AMF SD and RC, with the fenced plots being more favoured. Seasons significantly(p < 0.05) affected RC and SD. More RC and SD were observed in the wet period than the dry period. Correlating AMF SD and RC with soil physical and chemical properties showed no significant difference(p> 0.05) except for total nitrogen. Disturbance, vegetation cover density, season and total nitrogen are significant factors that control the dynamics and management interventions to maintain the forest health of dry Afromontane forests.

Impact of exclosures on wood biomass production and fuelwood supply in northern Ethiopia

In the Ethiopian highlands, communal grazing lands are one of the major land uses, and are source of livelihood for the rural people. Free and uncontrolled grazing in the communal grazing lands is the dominant grazing system. The traditional uncontrolled and free grazing system has caused severe degradation of the grazing lands. As a result, communities have started to establish exclosures and support the restoration of degraded communal grazing lands. Studies have shown that exclosures are effective to restoring degraded communal grazing lands and improving ecosystem services. However, studies that investigate the changes in aboveground biomass following the establishment of exclosures and compare it with fuelwood demand of the beneficiaries in our study area is lacking. Therefore, our study aimed at:(1) quantifying yearly biomass accumulation in exclosures and compare it to fuelwood demand of households that manage the exclosures;(2) assessing household energy sources and their consumption levels. To monitor changes in biomass production with over time, replicated(n = 3) 5 and10 year-old exclosures were sampled. To investigate fuelwood sources and consumption patterns, household surveys, key informant interviews and focus group discussion were conducted. Our results demonstrated that total biomass production increased with exclosure age. In both exclosure, biomass production from Vachellia etbaica was significantly(p \ 0.05) greater than that from Euclea.racemosa. Average daily fuelwood consumption per person was(0.63 ± 0.2) kg day^(-1). This means that the total biomass(27.5 Mg year^(-1)) obtained from 114.6 ha of exclosures covers only 9.4% of yearly fuelwood demand of the residents who manage the sampled exclosures. Nearly all respondents(95%) confirmed that they travel more than10 km day^(-1) to gather fuelwood from surrounding degraded forest patches. We recommend plantings of fast growing native tree species within exclosures and around homesteads to provide a sustainable fuelwood supply and using improved stoves to address the problem of fuelwood shortage. District agricultural offices could provide seedlings of native plant species, while communities provide unpaid labour for planting and managing plantations.

Effect of exclosure ages on woody plant structure,diversity and regeneration potential in the western Tigray region of Ethiopia

Exclosure is a method of rehabilitating degraded lands by protecting them from the interference of animals and from human encroachment, and is used to regenerate native vegetation as a way to reduce soil erosion, increase rain water infiltration and provide fodder and woody biomass in degraded grazing lands. Therefore, we studied woody plant structure, diversity and regeneration potentials in 5-and 10-year grazing exclosures in comparison with open grazed sites in a semi-arid environment. Data on species diversity, abundance, structure, basal area, frequency, density, and regeneration status were collected from 270 sample plots. Forty-one woody species representing 20 families were identified, with 18, 28 and 38 species found in open grazed areas, and in 5-and 10-year grazing exclosures, respectively. The 10-year grazing exclosures had a higher(P <0.05) species richness and plant densities compared to the 5-year grazing exclosures and the open grazed areas. The population structure and regeneration status of woody species in both grazing exclosures showed an inverted J-shape, indicating a healthy regeneration status, whereas hampered regeneration was observed in open grazed areas. The establishment of grazing exclosures had positive effects in restoring woody plant diversity and improving vegetation structure and regeneration potentials of degraded grazing lands.

Source of mycorrhizal inoculum influences growth of Faidherbia albida seedlings

Poor land use management and practice inhibit the growth and establishment of tree seedlings in dryland areas.We assessed arbuscular mycorrhizal fungi(AM)status of Faidherbia albida(Del.)A.Chev.trees grown on different land uses.We quantified the growth and nutrient uptake of F.albida seedlings inoculated with AM from different sources.These efforts were based on soil and fine root samples from the rhizosphere soils of F.albida trees.AM root colonization was determined using the gridline intersect method.Spores were extracted by the wet sieving and decanting method and identified to genus level.The seedling experiment had a completely randomized onefactorial design with four treatments and five replications.Faidherbida albida seedlings were grown in a greenhouse.All in situ F.albida trees were colonized by AM fungi.AM root colonization of F.albida trees was significantly higher(P<0.0086)in area exclosures than on lands used for grazing or cultivation.Spore abundance was significantly higher(P<0.0014)in area exclosures followed by cultivated land and grazing land.Glomus was the dominant genus in all land-uses.AM-inoculated F.albida seedlings grew better(P<0.05)than non-inoculated controls.Seedlings inoculated with AM from area exclosure had significantly(P<0.05)higher growth and nutrient uptake than those inoculated with AM from grazing and cultivated land.This emphasizes the importance of the native soil AM potential for better establishment of seedlings to achieve optimum plant growth improvement and assist in rehabilitation of degraded arid lands.

Arbuscular mycorrhizal fungi improve biomass, photosynthesis, and water use efficiency of Opuntia ficus-indica (L.) Miller under different water levels

Opuntia ficus-indica(L.)Miller is a CAM(crassulacean acid metabolism)plant with an extraordinary capacity to adapt to drought stress by its ability to fix atmospheric CO_(2) at nighttime,store a significant amount of water in cladodes,and reduce root growth.Plants that grow in moisture-stress conditions with thick and less fine root hairs have a strong symbiosis with arbuscular mycorrhizal fungi(AMF)to adapt to drought stress.Water stress can limit plant growth and biomass production,which can be rehabilitated by AMF association through improved physiological performance.The objective of this study was to investigate the effects of AMF inoculations and variable soil water levels on the biomass,photosynthesis,and water use efficiency of the spiny and spineless O.ficus-indica.The experiment was conducted in a greenhouse with a full factorial experiment using O.ficus-indica type(spiny or spineless),AMF(presence or absence),and four soil water available(SWA)treatments through seven replications.Water treatments applied were 0%–25%SWA(T1),25%–50%SWA(T2),50%–75%SWA(T3),and 75%–100%SWA(T4).Drought stress reduced biomass and cladode growth,while AMF colonization significantly increased the biomass production with significant changes in the physiological performance of O.ficus-indica.AMF presence significantly increased biomass of both O.ficus-indica plant types through improved growth,photosynthetic water use efficiency,and photosynthesis.The presence of spines on the surface of cladodes significantly reduced the rate of photosynthesis and photosynthetic water use efficiency.Net photosynthesis,photosynthetic water use efficiency,transpiration,and stomatal conductance rate significantly decreased with increased drought stress.Under drought stress,some planted mother cladodes with the absence of AMF have not established daughter cladodes,whereas AMF-inoculated mother cladodes fully established daughter cladodes.AMF root colonization significantly increased with the decrease of SWA.AMF caused an increase in biomass production,increased tolerance to drought stress,and improved photosynthesis and water use efficiency performance of O.ficus-indica.The potential of O.ficus-indica to adapt to drought stress is controlled by the morpho-physiological performance related to AMF association.

Exclosures restored the density and root colonization of arbuscular mycorrhizal fungi in Tigray, Northern Ethiopia

Introduction:Exclusion of grazing animals and tree plantations were among the methods used for the restoration of degraded lands in tropical semiarid areas.Exclosures can foster secondary forest succession by improving soil conditions and modifying microclimate for understory growth.This paper compared the arbuscular mycorrhizal fungi(AMF)spore density,root colonization of woody plants and soil chemical properties under exclosure with increasing age,and grazing land at different slope positions.Methods:The study was conducted in northern Ethiopia from 12 exclosure sites paired each with adjacent grazing land in total from 24 sites with four treatments replicated three times.In the entire study,216 plots were examined of which 108 were in exclosures and 108 in communal grazing lands.There were four age classes and three slope positions in each of the land uses.Composite soil and root samples were collected using nested plots measuring 100m2 from four sides of 1763 plants for spore enumeration and root colonization.Soils for chemical properties were collected from the four corners and center of 5 m×5 m plots.Results:All the 61 woody plant species that belong to 41 families were colonized by AMF.Spore density and root colonization were significantly higher in exclosures as compared to grazing land and increased with increasing ages of exclosures.Foot slope had significantly higher spore density and root colonization than middle and upper slopes.Soil chemical properties were significantly higher in the exclosure,oldest age of exclosure,and foot slope position(except P).AMF spore density and root colonization were significantly positively correlated with soil chemical properties.Conclusions:Exclosures are helpful to restore the AMF spore density and root colonization of woody species and soil fertility.

Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses.In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies.We compared the extent of interspecific competition with that of intraspecific competition.Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza(AM)and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A.etbaica and the slowly growing species B.papyrifera.A factorial experimental design was used.The factors were AM,two water levels and five species combinations Important Findings Seedlings of both species benefitted from AM when grown alone,and the positive growth response to pulsed water availability in B.papyrifera seedlings was in contrast with the negative growth response for A.etbaica seedlings.AM also affected the competitive performance of both species.B.papyrifera was not affected by intraspecific competition,whereas A.etbaica was negatively affected compared to the seedlings grown alone.This effect was stronger in the presence of AM.In interspecific competition,A.etbaica outcompeted B.papyrifera.Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition,and the aggressivity index of A.etbaica remained unchanged.The extent to which AM influences plant competition in a droughtstressed environment may depend on belowground functional traits of the species.AM and pulsed water availability could modify the balance between intraspecific and interspecific competition.By affecting the balance between intraspecific and interspecific competition,both factors could impact the establishment and survival of seedlings.

Carbon stock potential of scattered trees on farmland along an altitudinal gradient in Tigray,Northern Ethiopia

Introduction:Trees on agricultural landscape play a vital role in ecosystem services including food security that supports human livelihood.They can further offer synergy between adaptation and mitigation in addressing climate change impact.Understanding aboveground tree biomass and soil organic carbon stocks along the altitudinal gradient provide opportunities for better management of the carbon pools.However,little is known on how altitudinal gradient influences on carbon stock of woody biomass and soil of scattered trees on farmland,particularly in a dry area.Methods:The study area were stratified in to five class(500–1000,1000–1500,1500–2000,2000–2500,and 2500–3000 m a.s.l).Quadrats(100 m×50 m)were randomly selected from each of stratified altitudinal gradients.At every sampling point,one composite soil sample was taken at 60 cm soil depth for soil organic carbon analysis.For the purpose of woody biomass estimation,allometric equations developed for a similar area were used.Finally,aboveground biomass carbon(AGC),belowground biomass carbon(BGC),soil organic carbon(SOC),and total carbon stock(TC)status were estimated and variables were compared using one-way analysis of variance(ANOVA).Results:The result indicated that AGC,BGC,SOC,and TC varied significantly(p<0.05)along with an altitudinal gradient.The upper altitude(2500–3000 m a.s.l)AGC,BGC,SOC,and TC stock was estimated as 17.97 Mg C ha^(−1),6.53 Mg C ha^(−1),23.09 Mg C ha^(−1),47.59 Mg C ha^(−1) respectively,and significantly higher than the other altitudinal gradient.Conclusions:We conclude that scattered trees on farmland hold a high potential of carbon storage which may greatly contribute to the climate resilience green economy strategy and their conservation should be promoted.

Carbon stocks and sequestration potential of dry forests under community management in Tigray, Ethiopia

Introduction:Forests form a major component of the carbon(C)reserves in the world’s ecosystems.However,little is known on how management influences C stocks of woody vegetation,particularly in dry areas.We developed regression models for two dominant tree species to predict C stocks and quantified the potential of community managed forests as C sinks.Methods:Plots were randomly selected from community-managed natural forest,herbivore exclosures,and from communal grazing land.Tree and shrub biomass were estimated using a regression model on the most dominant woody species while herbaceous biomass was determined using destructive sampling.Results:The simplest model,based on only one single predictor variable,showed a good fit to the data for both species(Juniperus procera and Acacia abyssinica).Diameter at breast height(r2>0.95)was a more reliable predictor than height(r2>0.54),crown diameter(r2>0.68)(p<0.001).The C content of the total biomass for the managed natural forest and the exclosure were estimated as,58.11 and 22.29 Mg ha−1,respectively,while that for the grazing land was 7.76 Mg ha−1,and the mean carbon content between the three land uses were significantly different(p<0.05).Conclusions:We conclude that forests managed by the community have a high potential for C sequestration and storage and their conservation should be promoted.

Variations in soil properties and native woody plant species abundance under Prosopis juliflora invasion in Afar grazing lands, Ethiopia

Introduction:Pastoralism and agro-pastoralism are the major modes of life in arid and semi-arid rangelands.However,rangeland quality and quantity are rapidly deteriorating due to a number of natural and human-induced factors,one of which is bush encroachment.Little is known on how bush encroachment affects the ecosystem functions and services expressed in terms of the native vegetation composition and structure,status of the soil seed bank,soil chemical and physical properties,and the abundance of mycorrhiza spores.Methods:We assessed woody species in 64 plots distributed across four levels of Prosopis juliflora invasion(high,medium,low,and none)at two sites,Amibara and Gewane,in the Afar Region,Ethiopia.We collected composite soil samples to investigate the soil seed bank,mycorrhizal associations,and spore abundance.Results:Plant biodiversity was generally low,with eight and four woody species in Gewane and Amibara,respectively.Prosopis juliflora was dominant in highly,moderately,and lowly invaded areas while Acacia senegal dominated the non-invaded areas.The average number of P.juliflora individuals ranged from 3/ha at non-invaded areas in Gewane to 4200/ha at highly invaded areas in Amibara while the total individual number of native woody species ranged from 0 to 88/ha at highly and lowly invaded areas,respectively.The population structure of trees/shrubs in all invasion areas showed an inverted J-shaped distribution,characterized by a high abundance of small individuals.Prosopis juliflora invasion was associated with high soil OC,Na,Ca,P,bulk density,and moisture content.Herbaceous seed numbers and species richness were highest in the moderately and highly invaded areas.All sampled tree species were associated with mycorrhiza but the percentage of root length colonization by different arbuscular mycorrhizal fungus structures varied significantly(p<0.05)across invasion categories and sites.Conclusions:Our results revealed that although P.juliflora invasion negatively impacted the availability of native woody livestock forage species,it had a positive effect on most soil physical and chemical properties.Such variable effects call out for sustainable management practices when invaded areas are restored.

Dispersed trees on smallholder farms enhance soil fertility in semi-arid Ethiopia

Introduction:Dispersed trees such as Oxytenanthera abyssinica(A.Rich.)and Dalbergia melanoxylon(Guill.&Perr.)which are objectively maintained or planted on farmland provide a significant contribution to soil fertility improvement.However,there was no quantitative information on the level of soil nutrient additions of these trees to the soil system.Methods:This study was conducted on the farmers’fields in Kafta Humera district,Tigray region(northern Ethiopia),where mature stands of O.abyssinica and D.melanoxylon trees exist.Radial distance-based soil sampling(under the canopy,near to canopy,and far from canopy)was adopted to quantify the role of these trees on soil fertility improvement.Soil parameters tested were soil reaction(pH),total nitrogen(TN),available phosphorus(AvP),electrical conductivity(EC),cation exchange capacity(CEC),and organic carbon(OC).Results:There was a negative linear relationship between the radial distance of the O.abyssinica tree trunk and soil TN,OC,CEC,and AvP contents but not for pH.Similarly,negative linear relationship between distance from D.melanoxylon and TN,OC,and AvP was obtained.The average total nitrogen(0.26%and 0.13%),available phosphorus(7.21 ppm and 6.37 ppm),and organic carbon(1.73%and 1.02%)contents were respectively higher under the tree canopies of O.abyssinica and D.melanoxylon compared with the adjacent open canopies.The amount of soil OC,TN,AvP,and CEC under O.abyssinica tree species was also significantly higher by 69%,100%,13%,and 42%compared to that of D.melanoxylon tree species.However,the amount of EC and soil pH was significantly lower by 57%and 19%,respectively.Conclusion:In general,O.abyssinica and D.melanoxylon added a significant amount of nutrients to the soil.Thus,retaining these important tree species on farmland played a positive role in replenishing soil fertility for resource-constrained households so as to reduce chemical fertilizer amendments.