Early Establishment of Hybrid Poplar Under Alternative Silvicultural Management in Mountainous Japan

Successful establishment during the first growing season is essential for productive short-rotation coppice plantations, yet the effectiveness of establishment management under mountainous conditions remains poorly understood. We evaluated early establishment of one single hybrid poplar clone, Mori-no-Mirai 17, in mountainous Japan using a 2 × 2 × 2 factorial treatment structure comprising propagation type (rooted vs. unrooted cuttings), mulching (with vs. without mulch), and fertilization (with vs. without fertilizer). Survival and growth were assessed eight months after planting using mixed-effects models accounting for the experimental structure. Propagation type was the strongest determinant of establishment success. Rooted cuttings had significantly higher predicted survival than unrooted cuttings (50.4% vs. 32.5%). Mulching had a positive but non-significant effect on survival and did not significantly improve growth. Fertilization had no significant effect on survival, but the estimated increases in height and root collar diameter (RCD) under fertilization were greater for unrooted than rooted cuttings, narrowing differences between propagation types. Plot effects accounted for 20–28% of the total variation in height and RCD, indicating substantial fine-scale environmental heterogeneity. These findings suggest that the rooting status of cuttings at planting may be an important factor associated with early hybrid poplar establishment success under site conditions similar to those examined in this study.