Abstract: Typhoon-induced landslides in southeast coastal China are clustered in trees-covered slopes, suggesting potential interactions between trees and slope stability. Investigate the impacts of trees is crucial for slope stability analysis during typhoons. With this purpose, we conduct field tests, laboratory tests and dye tracer tests to investigate the root distribution and impacts of roots on soil properties. Results indicate that trees covered on slopes have a taproot system with a maximum rooting depth of 2 m. Tree roots enhance slope stability by providing additional cohesion to the soil but simultaneously create preferential flow paths that facilitate rapid rainwater infiltration. The contribution of preferential flow arising from root-soil gaps reaches 2 to 3 times greater than uniform shallow infiltration. These dual effects of root reinforcement and preferential infiltration significantly alter the mechanical and hydrological properties of the soil at the maximum rooting depth. During a typhoon event, the strong wind load, rainfall infiltration and trees jointly trigger landslides. The maximum rooting depth and bed-soil interface are two potential sliding surfaces within the slope. Our works provide new insights into the risk assessment of typhoon-induced landslides.