森林立地学会誌 森林立地48(2), 2006, 105109

Jpn.J.For.Environment 48(2), 105109  2006

 

中山間地における植林された耕作放棄地の増加と棚田跡の植栽木の成長

 

鳥居厚志・篠宮佳樹・田淵隆一**・吉永秀一郎**・酒井 武・酒井 敦***

森林総合研究所四国支所・**森林総合研究所・***国際農林水産業研究センター

 

 

Atsushi Torii, Yoshiki Shinomiya, Ryuichi Tabuchi, Shuichiro Yoshinaga, Takeshi Sakai and Atsushi Sakai : Increase in the area of afforested cultivated land in a mountainous area and growth of trees in plantations made after terrace paddy fields

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 obtuse) 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.

Key words : abandoned terrace paddy fields, terrace plantation, land use in mountainous area, productivity

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