Researchers in Japan have discovered a correlation between the height of Japanese black pine trees (Pinus thunbergii) along the coast and the depth of their roots. Taller trees tend to have deeper roots, which enhances their ability to withstand damage from tsunamis and severe winds. Their research indicates that encouraging deeper root development could enhance the resilience of coastal P. thunbergii, particularly in shorter trees. The study appeared in the *Journal of Forest Research.*
Researchers in Japan have discovered that taller Japanese black pine trees (Pinus thunbergii) along the coastline have roots that grow deeper into the ground. These deeper roots increase the trees’ resistance to damage caused by tsunamis and strong winds. The findings suggest that the resilience of coastal P. thunbergii may be enhanced by promoting deep root growth in shorter trees. This research was published in the Journal of Forest Research.
Many P. thunbergii trees have been established in Japan’s coastal forests due to their tolerance to salt and ability to thrive in nutrient-poor sandy soils. The trees’ strong, deep roots provide significant resistance against tsunamis, high winds, and blowing sand, offering essential protection for homes and farmland from natural disasters.
During the Great East Japan Earthquake of 2011, the coastal P. thunbergii trees significantly mitigated the impact of wave forces and debris from the tsunami. Nevertheless, some trees with insufficiently deep roots suffered severe damage and were washed away.
“If we can determine the depth of tree roots without excavating them, we can better identify which trees are more vulnerable to disasters,” explained Professor Yasuhiro Hirano from Nagoya University, who led the study. “Our team aimed to understand how the visible characteristics of P. thunbergii and the surrounding soil could help estimate root depth.”
The research team, including Hirano and Associate Professor Toko Tanikawa, began by excavating the roots of P. thunbergii trees along Aichi Prefecture’s coast. This allowed them to measure the maximum root depth while analyzing both the tree’s aboveground characteristics and the surrounding soil. They documented the root systems with 700 digital photographs from various angles immediately after excavation to avoid needing to transport samples to a laboratory.
In the lab, the researchers assessed the connection between the measured maximum root depth in the field and the aboveground traits of the trees, along with the soil conditions. They found a clear trend: as P. thunbergii trees became taller, their roots also extended deeper. This trend aligned with findings from previous studies involving 43 P. thunbergii trees in Japan.
Additionally, the team developed three-dimensional models of the root systems using the field photographs taken. “We created both surface and solid models of the root systems, enabling us to estimate the total root cross-sectional area at various depths,” Hirano noted.
The researchers’ results indicate that shorter P. thunbergii trees are more susceptible to falling due to insufficient root depth to withstand strong winds or large waves. “A high water table and compact soil near the coast can hinder deep root growth,” Hirano added. “Thus, improving drainage for high groundwater or softening the soil around shorter P. thunbergii trees might enhance the disaster resilience of coastal forests composed of these trees.”
