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.

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.