Abstract
To restore coastal forests heavily damaged by the tsunami following the Great East Japan Earthquake of March 2011, the Forestry Agency of Japan has been building berms along the coast in the damaged areas. These berms use sand (loamy sand) brought from adjacent hill areas as a growth base in which the seedlings of domestic tree species are planted. However, in these growth bases, soil surfaces are often covered with water because bulldozing and other heavy machinery has caused compaction of the soil, leaving it susceptible to submersion. The submersion of soils in water is problematic because of the potential for these conditions to interfere with the restoration of coastal forests. The aims of this research are to elucidate the cause of water stagnation in berms, and to evaluate the efficacy of countermeasures to combat water stagnation in these soils. Soils in berms at reforestation areas in Sendai are generally quite hard and dense, having no (massive) structure where the entire soil horizon appears cemented and very low water permeability. Some profiles have gley horizons in topsoil, caused by the reduction of Fe3+ under anaerobic conditions. We compared the effects of countermeasures on berms in these areas among the several types of tillage carried out using following machinery; the backhoe with a skelton-bucket, ripper-dozer, and plow/subsoiler. Soil hardness on berms decreased in all cases, although the passage times after execution of tillage were different (1- to 20-months). These findings indicate that the tillage for berms as a growth base were quite effective countermeasure at the depth of cultivated-soils and that the effects of them were kept up for at least 20-months.
