Impact of Michelia champaca and Tectona grandis mono-species and their mixed plantation on chemical soil properties in a tropical semi-evergreen forest

Abstract

Understanding the effects of planted forests on soil properties is of great importance to meet increasing demands for wood production and contributing to forest ecosystem services and soil carbon sequestration. However, the influence of mono- and mixed tree plantations on soil chemical properties remains incompletely explained, particularly in tropical semi-evergreen forests. In this study, a mono-plantation of Michelia champaca and Tectona grandis, as well as their mixed plantation, were studied on soil variables (pH, SOC, N, P, K) at different depths (0-10, 10-20, and 20-30 cm) in tropical semi-evergreen forest of the Khadimnagar National Park, Bangladesh. All examined pedovariables showed no significant differences among plantation types, notably in the surface soil layer (up to 10 cm). However, significant oscillations were found in the deepest soil layer (20-30 cm), where M. champaca and mixed-species plantations obtained the lowest SOC (0.55-0.66%) and N (0.05-0.06%) concentrations. In the intermediate soil layer (10-20 cm) K concentrations were the lowest in M. champaca (19.6 mg/kg) and mixed-species plantation (17.6 mg/kg), while T. grandis recorded the highest K concentration (27.4 mg/kg). Additionally, the results indicated an increase in pH with soil depth (from 5.30 in the topsoil to 7.00 in the deepest layer), with T. grandis showing the lowest values across examined soil layers (5.76-5.95) and significantly differing from M. champaca, which exhibited the highest pH over the soil profile (6.29-6.51). Such results suggest the leaching of basic cations (Ca2+, Mg2+, K+) over the soil profile due to pronounced monsoon rainfalls. Further research is necessary to fully elucidate underlying mechanisms behind the observed impact of examined plantations on chemical soil variables. Considering other variables such as litter chemical composition and various physical and microbiological soil properties can offer valuable guidelines for enhancing more sustainable management of a tropical semi-evergreen forest, prone to soil acidity and water erosion.