Recovery of saturated hydraulic conductivity along a forest successional series from abandoned land to mature, evergreen broad-leaved forest in eastern China

Saturated hydraulic conductivity (Ks) can be used to indicate changes in soil hydrology resulting from vegetation succession. A constant-head permeameter was used to investigate differences in Ks at five soil depths (10, 20, 40, 60, and 80cm) along a successional sequence of 155 years in evergreen broad-leaved forest at Tiantong National Forest Park, eastern China. The following six forest successional classes were studied: climax evergreen broad-leaved forest (CE), sub-climax evergreen broad-leaved forest (SE), evergreen broad-leaved mixed coniferous forest (MF), coniferous forest (CF), secondary shrub (SS), and abandoned land (AL). Surface Ks (the geometric mean of Ks at 10 and 20cm soil depths) significantly increased from AL to CE but declined in CF. The surface Ks value under CE was higher than under other successional stages (CE 271mmh ^-1, AL 58mmh^-1, SS 124mmh^-1, CF 90mmh ^-1, MF 170mmh^-1, SE 231mmh^-1), and was 4.7 times greater than under AL, 2.2 times greater than under SS, and 3.0 times greater than under CF, but showed no significant difference from SE (P>0.05). Vertical difference of Ks was detected up to a soil depth of 40cm along forest successional series. Macroporosity was the main determining factor and played an important role in the process of Ks recovery. The likelihood of overland flow generation was inferred by comparing Ks at soil depths of 10, 20, 40, and 60cm under the various successional stages at prevailing storm intensities. Overland flow was most likely to occur in the early successional stages. This study suggests that Ks could be restored to climax forest levels along forest successional series, but the recovery time could be as long as 95 years.