Vegetation of the Basin of River Simatagawa

This article is the report of the writers' ecological research submitted to the Simatagawa-Tyosakai (The Board of the Investigation into the River Simatagawa of the Yamaguti University), dealing with the vegetation of the basin with the object of planning to effectually keep the source and volume of water of River Simatagawa.The River Simatagawa rises among the Sy&nan Plateau and theRenge range of mountains, and empties into the Seto Inland Sea. The area of the basin is estimated to be 250.45km2. The annual rainfall is 2,'l^mm. at Takamori, and 20SCmm. at Kudamatu. The upperstream of the river is much blessed with the rainfall and the nature of soil.The vegetation is mostly composed of the secondary forests of Pinus dsnsiflora, where the undergrowth is quite poor and the flow from the soil is rather great on the other hand.The original forests might not be the pine forests, but the forests of Castanopsis ruspidata. In the region of the downstream the very forests are often mixedwith Castanopsis ruspidata var. sieboldii, and the region of the upper-stream they are mixed with Quercus glauca. These forests may have good effect upon the maintenance of the river source, keeping the plentiful volume of water and moreover being useful to protect the region from the disastrous flood. It is specially advisable to preserve and bring up the forests Laurisilvae in this region.