Abstract
Broadleaf trees in coastal forests are expected to reduce tsunami damage, act as windbreaks, and reduce soil
erosion. Trees with strong and deep root systems are desirable for providing these ecosystem services, but root
development can be affected by soil properties, especially when trees are planted on consolidated soils. We assessed
the trunk and root growth of planted broadleaf trees in relation to soil properties in four plots in Akita and Chiba
Prefectures, Japan. Two plots in Akita prefecture, Mukaihama and Hamayama, contained deciduous broadleaf
trees (including Quercus dentata and Zelkova serrata) planted on sand dunes. The remaining two plots in Chiba prefecture, Futtsu and Komatsu, contained evergreen broadleaf trees (including Machilus thunbergii and Quercus phillyraeoides) planted on embankments of consolidated soil. Pinus thunbergii was planted in all plots. Diameter at breast height, tree height, and soil hardness were assessed and the roots of two to four trees of each species were excavated in each plot. The lengths of vertical and lateral roots >1 cm in diameter were measured and we compared
the depth of the consolidated soil layer to root length. In Hamayama, the vertical roots of P. thunbergii and some roots of Q. dentata and Z. serrata extended below the consolidated soil layer, which was 1 m in depth. Although the soil was extremely soft at Mukaihama, tree growth was poor due to oligotrophic conditions and strong winds. In Komatsu, where trees had been planted a decade previously, the consolidated soil layer was found at a depth of
approximately 30 cm, whereas at Futtsu it was found at depth of 70 cm because of aquifer was found at 80 to 100
cm in depth. We therefore concluded that root growth in coastal forests is affected by soil hardness as well as tree
attributes and other soil properties.
