Acknowledgement
We thank Takashi Saitoh, Osamu Kishida, and Shiro Tsuyuzaki for their helpful and insightful comments on the manuscript. We also thank Rei Sakai, Michio Ishihara, Yoshiaki Takahashi, Masayuki Watarai, Wataru Mamiya, Toru Miyazaki, and members of Uryu Experimental Forest, Hokkaido University, for their field assistance. This research was supported by JSPS KAKENHI Grant Numbers 16J03194 to SK, 16H06179 to SU, and 19H02974 to SU.