<p>The channel forest is believed to possess the capability to regulate debris flow; however, its sediment trapping effect remains unclear. This study investigates the influence of tree trunk volume fraction (the proportion of trunk cross-sectional area to the woodland area and ranging from 0.9 × 10⁻³ to 88.6 × 10⁻³) on the deposition patterns and impact force of debris flow through a series of physical experiments. Upon entering the wooded channel, the velocity of the debris flow declined while the flow depth raised, eventually reaching a state of equilibrium in the new resistance environment. Simultaneously, a significant volume of sediment was trapped within the wooded channel. The deposition height decreased gradually from upstream to downstream, leading to an increase in bed slope within the forested area. The peak impact force attenuation rate ranged from 15.8 to 79.0%, while the sediment retention rate varied from 3.0 to 31.7%. Notably, peak impact force attenuation rate showed the strongest correlation with the relative opening, whereas the sediment retention rate exhibited the strongest relationship with the initial resistance energy slope of forest. It was observed that viscous debris flows exhibited a slightly lower peak impact force attenuation rate than diluted debris flows, whereas the opposite was true for the sediment retention rate. The bed slope increment caused by sediment deposition in wooded channel ranged from 0.002 to 0.089 and demonstrated a proportional relationship with the initial resistance energy slope of woods. Specifically, for viscous debris flows, the proportional coefficient was 2.3%, and for diluted debris flows, it was 3.4%. This study also introduces novel calculation methods for calculating the deposition slope and estimating potential sediment retained volume in wooded channels.</p>