EFFECT OF SLOPE GRADIENT ON VEGETATION AND SOIL ATTRIBUTES OF GARA ADES PROTECTED VEGETATION IN WESTERN HARARGHE ZONE OF OROMIA REGION, ETHIOPIA

The study was conducted at Gara Ades protected vegetation of Doba woreda, Western Hararghe Zone, Ethiopia; from October to December 2017 with the objective of analysing the woody vegetation structure, diversity and regeneration status, as well as soil status potentials under three slope gradient classes. Primarily, slope classes were set purposively; where lower slope class was (LSC: 10 - 20 %) and upper slope class was (USC: >20 - 0.05) different in the LSC, MSC and USC which is predominantly loam and sandy loam contents but, textural class of silt of LSC was significantly (P < 0.05) different from two groups (MSC and USC). Silt textural class of the study soil was influenced by the difference in slope gradient classes. However, soil chemical parameter analysis shows that except phosphorus (P), all parameters have a significant (P < 0.05) difference among slope classes with different mean values. Soil pH, EC, Ca, Mg, Na and TN parameter mean values were higher in the LSC and have significant difference from MSC and USC. Soil OC, OM and CEC parameters have higher mean values in MSC (MSC was significantly different from LSC and USC). LSC has lower Soil K mean value which was significantly different from MSC and LSC. Soil EA was higher in USC and the mean value of USC was significantly different from MSC and LSC. Results of this study revealed that, slope gradient showed variation in vegetation and soil measurement parameters. Generally, LSC has lower woody vegetation mean values than MSC and USC; where slope gradient increase had a positive effect on woody species diversity and composition. On the other hand; LSC has higher herbaceous plant dry matter yield, herbaceous plant basal cover and soil physico-chemical property mean values than MSC and USC; hence slope gradient increase had a negative effect on herbaceous plant dry matter yield, herbaceous plant basal cover and soil physico-chemical property parameters. More than woody vegetation herbaceous and soil parameters are more influenced with an increase in slope gradient. In general, disparity of slope gradient should have to be considered during further ecological studies in the study area to reduce variations that occur due to slope gradient variation. Additionally, human and livestock intervention were also expected to be serious challenges in vegetation structure and composition of Ades protected vegetation. Therefore, better ecological, socio economic and policy concerns should have to be adopted and established in the study area for a better management to increase the productivity of the forest without depletion of the available vegetation and soil resources.