Impacts of Wenchuan Earthquake-induced landslides on soil physical properties and tree growth

How earthquake-induced landslides impact the growth of existing trees remains unknown worldwide. Therefore, we established an experiment with two tree species (Cupressus funebris, Cryptomeria fortunei) and two landslide conditions (non-impacted and impacted stands) near the northern section of the fault belt one year after the Wenchuan Earthquake (8.0 Ms) that occurred in China in 2008. At site I, two plots of each species were located in non-impacted stands. At site II, three plots of Cu. funebris were established in non-impacted stands, and three plots were established in impacted stands. At site III, three plots of Cr. fortunei were placed in non-impacted stands, while two plots were placed in impacted stands. All plots were 20 m × 20 m in size. At each plot, we measured the diameter at breast height and the height of each tree and used their mean values to select five trees representing average growth. Two to three small fine roots (≤2.0 mm in diameter, >20 cm long) were sampled in just three of the five selected trees to investigate root parameters. Leaf, branch and root water contents of the sampled trees were also examined. Soil samples were collected from 0 to 10, 10 to 20 and 20 to 40 cm depths at the center and near the four corners of each plot to analyze soil physical properties. The study revealed that saturated water content, capillary moisture capacity, field water capacity, total porosity and capillary porosity were lower in the impacted stands than in the non-impacted stands. Conversely, bulk density was higher in the impacted stands, indicating that the soils in the impacted stands had become compacted and dry. Soil water content, saturated water content, capillary moisture capacity, field water capacity, total porosity, capillary porosity and non-capillary porosity were greater in Cr. fortunei stands than in Cu. funebris stands, while bulk density was lower, indicating that impacted stands of Cu. funebris were more compacted and dry than those of Cr. fortunei. In impacted Cu. funebris stands, mean tip length/length and mean tip length/biomass decreased, while plant organ water contents did not change. In impacted Cr. fortunei stands, in contrast, these root parameters as well as specific root area, specific root length and leaf water content increased. These patterns suggest Cr. funebris experiences a much higher root growth than Cu. funebris in landslide impacted stands. Survival and recovery may be more difficult for Cu. funebris than for Cr. fortunei.