Forest Denudation by Passage of Heavy Vehicles

At Shimamatsu maneuver field (Hokkaido district) with the area of 5, 450ha, the soil survey was made to clarify the influence of the frequent passage of heavy vehicles on soil properties such as a hardness, infiltration capacity, depth of frozen soil and so on, during the period from 1962 to 1963. 21-surveying plots were selected from the whole field referring to the air photographs. These plots were classified into the three grops as follows: group I was the forest land with dense vegetation, group II the land with little waste vegetation, and group III the extremely waste land. The results may be summarized as follows: 1. The degree of slope in the field was from 1/8 to 1/4.5 with the mean value of 1/5.6. The soil at surveyed plots was the sandy loam belonging to volcanic ash series. The vegetation in the group III has been extremely wasted and become the bare-land because of the frequent passage of heavy vehicles. The soil hardness was larger for the group III than for the group I. 2. The infiltration test of soil samples using a rain simulator indicated that the infiltration capacity was larger for group I than for the group III. As shown in Fig. 5. the rain water applied to the samples from the group III flowed out immediately as a runoff after the beginning of the rain. This fact implied that the water-holding capacity for the group III soil was negligibly small. The runoff for the group I was hardly observed, and the most of rain was infiltrated into the soil. On the other hand, the runoff for the group II occurred in parallel with the infiltration. It was also found that the amount of runoff increased proprtionally to the soil hardness. 3. The depth of frozen soil layer was observed to be smaller for the group I than for the group III, because of the existence of dense vegetation at the group I. 4. It is reasonable to point out that dam making may be effective to prevent the soil erosion from the waste land caused by the frequent passage of heavy vehicles, but the adoptation of the tree planting method may be more effective for the soil conservation at extremely waste lands.