2025 Volume 107 Issue 9 Pages 199-207
We investigated the effects of a soil water gradient on the growth of Pinus thunbergii saplings planted in a coastal forest restoration site in Iwanuma, Miyagi Prefecture. Saplings were planted on a mound made of ‘yama-suna’ in autumn 2018. However, there was no water outlet for the drain, and large pools of water were often observed on the site following rainfall. Furthermore, the area beyond the seaward edge of the mound was covered in gravel. Trees in the seaward portion of the site exhibited higher sapling mortality and terminal bud mortality, and restricted tree height and elongation of terminal shoots and needles. Sapling growth was likely to have been inhibited by severe water stress, caused by a large embankment at the seaward side of the study site, rather than sea breezes. Indeed, soil water content was higher in the seaward portion of the site, as well as in rows planted adjacent to the drain or woodchip mulch, compared to other rows. Our results imply that the gravel outside of the mound led to poor drainage; moreover, the lack of a water outlet for the drain, along with mulching, inhibited soil respiration and thus contributed to the excessive soil water. Based on our results we recommend installing drains at the edge of the seaward side of the mound, installing a water outlet for the drains, and removing the mulch.
