Soil water movement changes following conversion from evergreen and deciduous broad-leaved mixed forests to Chinese fir plantations

Purpose This study was aimed at exploring the differences in soil water movement after the conversion of evergreen and deciduous broad-leaved mixed forests (natural forests (NF)) to Chinese fir ( Cunninghamia lanceolate (Lamb.) Hook.) plantations (CFP, 20–21 years old) in the Peng Chongjian watershed, Jiangxi Province, China. Materials and methods The soil capillary porosity, noncapillary porosity, total porosity, and bulk density were used a cutting ring to measure. Particle-size distribution (PSD) was measured with a Malvern Laser Particle Sizer 3000, and fractal dimension ( D ) was calculated on the basis of measuring the PSD. An immersion method was used to simulate the water-holding process of the litter. Soil water contents and isotope compositions were applied to investigate the water movement along soil profile. Results and discussions The results showed significant changes in PSD and D of top soil (0–20 cm) after the conversion from NF to CFP. After a heavy rain event (37 mm) in the rainy season, the mixing process of the previously D-enriched soil water with rainfall was observed in NF and CFP. However, in NF, the response to rainfall was strongest on July 11 th (fourth day after rainfall), but in CFP, the strongest signal of rainfall took place on July 8 th (first day after rainfall). The isotopic characteristics of the NF and CFP soil profiles retained the dynamics that were present before the rain, and the water moved in the soil in the form of translatory flow. Conclusions Our results show that soil water moves as translatory flow in both NF and CFP; after the conversion from NF to CFP, the water conservation capacity enhanced. What is more, soil properties are improved than NF after forest conversion under the influence of eco-forest protection policy.