In order to clarify the increase in the area of abandoned cultivated land and the growth of plantations made after terrace paddy fields in a mountainous area of Tosa town, Kochi Prefecture, we analyzed the area's land-use history by using aerial photographs and performed stem analysis of planted trees. The results of land use analysis showed the area of abandoned cultivated land has increased gradually from the 1960s to the 1990s. The increase may have resulted from a political reduction of acreage and depopulation of mountainous areas. Most abandoned cultivated lands had been afforested ("terrace plantations") but those abandoned in recent years tended to be simply abandoned. We surveyed 12 plots in 12-to-33-year-old Sugi (Cryptomeria japonica) or Hinoki (Chamaecyparis obtusa) plantations that had been made after abandonment of the terrace paddy fields. Complete enumerations of each plot and stem analysis of the standard trees were carried out. The results of the stem analysis showed that the tree growth in the terrace plantations was generally excellent, both in height and in diameter, and the productivities of the abandoned paddy fields were generally classified into the sites as productivity class I. However soil conditions in the terraces tended to be too wet for these species, and it may be necessary to improve drainage by means of digging drain ditches and planting holes with enough depth to penetrate the former plowsole. The results of this study and of previous related studies suggest that terrace plantations might be presumably worthwhile for forestry as well as useful for environmental improvement, conservation of water resources, prevention of soil erosion, absorption of carbon dioxide, and so on.
