Coniferous Tree Species Effects on Soil Chemical Characteristics in Goro-Gutu District, Eastern Ethiopia

The fast growing natures of conifer tree species and favorable economic returns from these trees have encouraged the conversion of natural grasslands in open forests into tree plantations in Ethiopia. The dominant tree species used for this purpose in open forest areas of Eastern Oromia were Podocarpus falcatus, Juniperus procera and Cupressus lusitanica. These tree species plantations are spreading rapidly in mountain areas, specially, in protected open forest areas. However, how different tree species affect soil chemical nutrients of the open areas after plantation is remain largely unknown. Thus, the study was conducted at Keramile open forest of Goro-gutu district, Eastern Ethiopia, to evaluate the effect of coniferous tree species on grassland or open areas found in the open forest. The coniferous tree species used for our study were Podocarpus falcatus, Juniperus procera and Cupressus lusitanica. The current study investigated the soil chemical contents under the three tree species canopies, outside canopies as well as the interactions between tree species and canopy covers. Our results showed that the evaluated coniferous tree species had significant effect on soil pH, cation exchange capacity (CEC), organic matter (OM), total nitrogen (TN), organic carbon (OC), available phosphorous (av. P) and sodium (Na); in which soil pH, TN, OM and OC contents were significantly higher under P. falcatus than J. procera and C. lusitanica tree species. But no significant difference was detected in soil pH, TN, OM and OC contents between J. procera and C. lusitanica tree species. The present results also revealed that the canopy cover and their interaction had significant effect on soil OM, pH, OC, av. K, TN, EC, Na and CEC; were significantly higher OM, pH, OC, av. K, TN and CEC were obtained in the outside canopy than under the tree canopy cover, whereas soil EC and Na contents were higher under canopy than outside canopy cover. However, no significant difference was observed between under canopy and the outside canopy in soil av. P, Ca and Mg contents. Generally, our study showed that the coniferous tree species evaluated had negative impact on soil chemical properties (OM, pH, OC, av. K, TN and CEC) of the open or grassland of the study area. Therefore, management and monitoring of soil chemical characteristics of grassland found in open forest is crucial in Keramile open forest, Goro-gutu district, Eastern Ethiopia and other open woodlands receiving similar practice.