Changes of preferential flow in short-rotation eucalyptus plantations: field experiments and modeling

Abstract

As an important part of the hydrological cycle, preferential flow significantly improves infiltration properties and limits the ability of soil to store, filter, and buffer water. However, the effect of roots on the preferential flow infiltration process in forest ecosystems is still unclear. This study measured the preferential flow infiltration process in short-rotation eucalyptus plantations (four forest ages of 1, 2, 3, and 5 years) with the surface-positioned double-ring infiltrometer in south subtropical area, China. Overall, the cumulative infiltration (CI), initial infiltration rate (IIR), and stable infiltration rate (SIR) increased with forest age. The CI, IIR, and SIR of the 5-year-old eucalyptus plantation were the highest in four aged eucalyptus plantations. Correlation analysis showed that root biomass was positively and significantly correlated with CI (p < 0.05), IIR (p < 0.01), and SIR (p < 0.01), which showed that the preferential flow increased with root biomass. However, the correlations between total porosity (TP) and IIR, SIR, and CI were all not significant (p > 0.05). The dye coverage of the inner and outer ring tangents, which were used to observe the strength of lateral preferential flows, was significantly and positively correlated with CI (p < 0.01), IIR (p < 0.01), and SIR (p < 0.01). The dye coverage of the outer ring tangent was significantly and positively correlated with root biomass (p < 0.05). So, the lateral preferential flows depended on root biomass and increased with forest age. The Horton model, which had higher stability and accuracy than the Kostiakov and Philip models, was the most suitable model to describe the preferential flow infiltration process in eucalyptus plantations. As important factors influencing the evolution of preferential flow in eucalyptus plantation, root biomass was used in predicting the parameters of the Horton model through regression analysis. Then, a unified model predicting the preferential flow infiltration process in short-rotation eucalyptus plantations was proposed and verified. This study achieved the quantitative measurement of preferential flow infiltration process, explored the importance of roots in the production of preferential flow channels, and found the lateral preferential flow played an important role in infiltration in forests. These results can provide a theoretical basis for improving the efficiency of water resource management in plantation, and optimizing the model of preferential flow infiltration process in plantation.