Early Establishment Responses of Quercus acutissima to Planting Stock Size, Wood Chip Mulching, and Relative Planting Density in Southern South Korea

Successful establishment of planted trees is critical for forest restoration, particularly when post-outplanting drought occurs. We evaluated associations of planting stock size, wood-chip mulch depth, and relative planting density with the soil microenvironment, survival, and growth of Quercus acutissima over 43 months in a single-site field experiment in southern South Korea. A total of 132 trees were planted in 36 plots, with one plot per treatment combination. Survival was analyzed using interval-censored proportional-hazards models, and growth was assessed among surviving trees using relative growth rates and absolute growth increments. Of 49 final mortality episodes, 43 were first recorded during the first growing season. Relative to R2, mortality hazards were higher for R6 (HR = 5.49, 95% CI: 1.26–23.88) and R8 (HR = 5.10, 95% CI: 1.05–24.86). Relative to no mulch, hazard estimates were lower for 5 cm (HR = 0.36, 95% CI: 0.08–1.60) and 10 cm mulch (HR = 0.19, 95% CI: 0.05–0.83), with clearer evidence for 10 cm. Mulching was also associated with reduced early soil-moisture variability. Relative planting density showed no detectable association with survival, but high relative density was associated with lower early soil moisture and reduced root collar diameter growth. These findings suggest that planting treatments should be considered in relation to site conditions.