森林立地学会誌 森林立地44(1),2002,1〜10

Jpn.For.Environment 44(1),1−10  2002

 

Changes in soil movement after forest clearing in the main island of

Okinawa, southwestern Japan

 

Yasuhiro Ohnuki*

Forestry and Forest Products Research Institute (F.F.P.R.I.), Tsukuba, Ibaraki 305-8687, Japan

 

  In the main island of Okinawa, inflow of “reddish soil” caused by development projects has damaged the ecosystems of coral reefs. The conversion of hillslopes into farmlands and housing areas and the construction of roads in woodlands have been reported to be the causes of soil erosion. However, the effect of felling on soil erosion has not been elucidated. To determine changes in soil erosion rates after forest clearing, the amounts of soil movement in a cutover basin on the main island of Okinawa were measured. The results of measurements showed that 1the amount of soil movement in the cutover basin was greatly decreased when most of the surface of the slope was covered by understory vegetation; 2the amount of soil movement differed according to soil type, with the largest soil movement occurring in the case of surface gleyed red and yellow soils, the second-largest soil movement occurring in the case of yellow soils, and the least soil movement occurring in the case of red soils.

  

  大貫 靖浩:沖縄本島における皆伐後の土砂移動量変化

 沖縄本島においては,種々の開発により生産された赤土の流人が珊瑚礁生態系に被害を与えている。丘陵地における農地・宅地造成や,林道の開設が土壌侵食の要因とされているが,森林伐採が土壌侵食に与える影響についてはよくわかっていない。そこで筆者は,皆伐後の土壌侵食量の変化を明らかにするために,沖縄本島の伐採された流域において土砂移動量を測定した。その結果,1)伐採流域における土砂移動量は下層植生が斜面をほとんど被覆したときに急激に減少する。2)土砂移動量は土壌型毎に異なり,表層グライ系赤黄色土で最も多く,次に多いのは黄色土で,赤色土が最も少なかった。


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