Comparison of soil hydraulic properties between cypress and cypress-cedar mixed forests

Introduction Some crucial soil functions such as hydraulic conductivity (K-) and water retention (-) relationships are controlled by the spatial soil-pores structure. Researches on them are essential to reveal many theoretical and practical topics such as forest flood mitigation mechanism and rainfall infiltration function in forest hydrological processes. Many researchers are focusing on how factors like land-use, forest slope, and human activities affect the soil properties (e.g., Lipovetsky et al. 2020). As well, researchers stated that forest tree species affect forest soil properties significantly through influence the factors like organic component, root system and soil-pore system (e.g., Calvaruso et al. 2006). More studies are needed to reveal how variability of tree species influences hydraulic properties through soil-pores system. This study will focus on the comparison of forest soil hydraulic properties and soil-pore connection properties between cypress-only forest and cypress-cedar mixed forest. Method and Study sites We collected soil samples every 10 cm depth using the soil core samplers (height 5.1 cm, volume 100cm3) from the two study sites, the Kamigamo Experimental Forest Station with Japanese cypress forest and the University of Tokyo Chiba Forest with Japanese cypress and Japanese cedar mixed forest. Both sites are underlain by on sedimentary rock. The Continuous Outflow Evaporation Method (COFEM) (Masaoka and Kosugi, 2021) and the Improved Evaporation Method (IEM) (Masaoka and Kosugi, 2018) were used for soil hydraulic properties measurement which measure the K- and - curves synchronously. Meanwhile, the soil-pores conductance, C(r), which means the hydraulic conductance of soil-pore with radius r, was estimated. Results and conclusions The result of parent material layer showed two sites have the similar tendency in K- and - curves, though the Chiba samples showed smaller K and larger values when <-40cm. Top soil layer showed no significant difference in K- curves. However, it showed differences in - curves with which the Chiba samples have larger at dry range (<-30cm). They also have different C(r) trait that the Chiba samples have larger C(r) in small soil-pores size. It was suggested that small soil pores in mixed forest have larger hydraulic conductivity.