GISを用いた丹沢山塊, 桧洞丸山頂付近のブナ林衰退と地形条件の解析 Analysis of Topographical Factors and Deterioration of Beech Trees around the Top of Mt. Hinokiboramaru, Tanzawa, Using GIS
There have been reports on the deterioration of beech (<i>Fagus crenata</i>) forests in the Tanzawa Moun-tains. Topographical factors are considered as being important in finding the cause for this, but there have been no quantitative investigations. On the other hand, with the recent advances in geographic information technologies and the improvement of the digital elevation model (DEM), more efficient work and quantitative assessment along with visualization are possible. This paper aims to investi-gate the situation of deterioration in this district spatially, and to examine the topographical condi-tions by utilizing geographic information technology. The study area, around the top of Mt. Hinokibora-maru in the western part of the Tanzawa Mountains, the areas in the Tanzawa Mountains with the most severe deterioration, has been selected.<br> First, distortion caused by the topographical unevenness of an aerial photograph is corrected using DEM. In correcting distortion, existing methods are inappropriate for this research because they require special facilities and software. Therefore, a comparatively simpler method was developed and used instead.<br> Second, degrees of deterioration are investigated using aerial photographs. The forest was classi-fied into three categories: badly decayed areas; semidecayed areas; and areas without decline. The badly decayed areas are where the ground surface is visible due to the collapse of trees, and semi-decayed areas are where trees without canopies are found.<br> Interpretation of aerial photographs has thus corrected the distortion caused by topographical unevenness. Also, in order to investigate the precision of interpretation, the Global Positioning System (GPS) is used as well, and spot investigation is carried out. As a result of inspection, aerial photographic interpretation and spot investigation results clearly conform.<br> A distribution map of decay made up in this way is represented as a bird's-eye view image using the Geographic Information System (GIS), allowing for visualization of the relationship between the distribution of deterioration and topography. In this way, it was verified that badly decayed areastend to concentrate near the mountaintop and stretch along the ridges.<br> The relation between deterioration and topographical factors, such as altitude, inclination angle, and slope direction, was also clarified statistically. Results show that badly decayed areas can be seen over 1250m a.s.l. and are concentrated over 1500m a.s.l., that they are relatively widespread on gentle slopes, and that they are concentrated on slopes facing south.<br> This paper quantitatively verifies that the deterioration has a strong relationship with topographi-cal factors. Also, by using geographic information technology, the efficiency of work and quantita-tive assessment has been attempted, bringing about effective results. The results can be considered useful in further investigations concerning this particular topic.
- 地理学評論. Ser. A
地理学評論. Ser. A 71(7), 505-514, 1998-07