Long-Term Impacts of Conifer Afforestation on Forest Floor Development and Soil Properties in Herbaceous Rangelands Under Semi-Arid and Sub-Humid Climates

Abstract

This study examined the effects of afforestation on selected hydro-physical and chemical soil properties, forest floor development, and its chemical content following the conversion of herbaceous vegetation-covered rangelands into coniferous forests with Cedar of Lebanon (Cedrus libani) and Austrian pine (Pinus nigra) in Elaz & imath;& gbreve;, T & uuml;rkiye, under semi-arid and sub-humid climatic conditions over approximately 60 years. The research also examined the forest floor characteristics developed in these afforested areas. Afforestation with P. nigra did not significantly affect soil hydro-physical properties in either climate. However, C. libani resulted in notable improvements, especially under sub-humid conditions. In these areas, field capacity increased from 18.6% to 23%, permanent wilting point moisture from 12.05% to 14.29%, and available water capacity from 6.58% to 8.72%. Bulk density decreased from 1.10 to 0.99 g/cm3, enhancing porosity, aeration, water retention, and reducing erosion sensitivity. In contrast, C. libani had negative effects under semi-arid conditions, increasing bulk density (1.16-1.28 g/cm3) and reducing moisture retention. Chemical changes were limited overall. In semi-arid areas, C. libani reduced calcium and sodium, while P. nigra lowered nitrogen content. Both species increased magnesium in sub-humid areas while decreasing carbon and nitrogen levels. The forest floor in the afforested areas was very thin and weakly developed. While the leaf layer was present in all plots, the humus or fermentation layers were sometimes absent. In conclusion, C. libani showed more positive impacts on topsoil's hydro-physical and chemical properties than P. nigra, particularly under sub-humid conditions, supporting its potential for afforestation in similar climate conditions.