Forces which cause the change of landforms are divided into three: (1) endgene force, (2) exogene force, and (3) human force. In the ancient time, when human culture was yet low, man lived in adapting to the conditions of natural environment, and did not change landforms in a great amount. But in the recent years, human forces are conspicuous to change landforms: such as, upheaval of river-beds by riparian works; deposition of sand and gravels in artificial lakes by construction of dams; land subsidence in industrial areas by puming up of ground water. In the ice age, valleys in mountains of Northern Japan were covered by peri-glacial block streams, but in the post-glacial age, these block streams are covered by dense forest. When we cut the forest for various purposes, the underlying block streams seems to begin to move and become the cause of natural hazard of land-slide.
Durch die neue Entwicklung der Industrien und der Städte wird die japanische Vegetation heute sehr rasch und stark verändert und verarmt. Besonders stark ist diese Tendenz, wo neue Technik konzentriert und hohe Finanzmittel ausgegeben werden. Die Vegetationskartierung liefert für die sachliche Beurteilung der Verarmung unserer Vegetation die besten Möglichkeiten. Seit 10 Jahren haben wir an mehr als 50 Orten Japans die Vegetation kartiert (Vergl. Literatur). Durch unsere Karten der realen Vegetation und die Karten der potentiellen natürlichen Vegetation konnten wir die Veränderung und Verarmung der Vegetation nicht nur in den großen Städten und neuen Industrie-Bezirken, sondern auch einseitige forstwirtschaftliche Nutzung (Kahlschlag, Monokulturen u. a.) sowie durch touristische Anlage, wie den Bau von Bergwegen u. a. in fast ganz Japan feststellen. Für die Schaffung einer neuen vegetationsreichen Umwelt sollte die Vegetationskarte als die am besten geeignete Grundlage gewählt und benutzt werden.
Firstly, the structure, regulation, balance and metabolism of Japanese subalpine coniferous forest and Britisch temperate deciduous forest ecosystems, both being the study areas of the International Biological Program (IBP), were elucidated. Secondly, the present state of the destruction of ecosystems caused by human impact was examined in the artificial forest, artificial grassland, cultivated land, rural, urban and industrial areas, marine, coastal and water areas of Japan. And thirdly, regeneration of destructed ecosystem through the course of ecological succession was discussed.
In this article, the following 4 themes of climatic change are discussed critically. 1. Morphology and scale of climatic change. 2. Post-glacial climatic change. 3. Recent change in the mean sea level. 4. Man-made modification.
Human activity has profoundly affected rivers and streams in recent Japan. Because of rapid socio-economical development in past one hundred years, patterns of land untilization has changed especially high-developed regions where flood control works has been vigorously executed. As a result of use of large scale longitudinal embankments as flood control measures, the flood flow became on a huge scale in major rivers. In addition, in accordance with development of urbanization during these ten or fifteen years, the runoff coefficient of storm rainfall in a river basin to river course increase due to the rapid change of paddy fields and forests along the river into residential areas as well as traffic routes pavement. As a result, floods in urbanized area has an increasing tendency.
Based on the recnt available data, the most of the present deltaic plains in the coastal areas of Japan probably began some 5, 000 years ago, following the virtual cessation of the eustatic rise in sea level. Subsequent sea level oscillations of small amplitude may have occurred since that. The sea level during the Yayoi period (about B. C. 300-A. D. 300) was lowered about 2 meters below present sea level and they would have had an effect on the rapid growth of the deltaic plains. In early historic times (about A. D. 4th century to 10th century), the sea level should have rised higher than the present one. In this time, consequently, the growth of the deltaic plains was slow. Generally, in the deltaic plains with altitude of less than 5 meters, the remains of the Yayoi period are now found at depths of about 1-2 meters under surface soil. The remains are overlaid with fluvial sediments of 1-2 meters thick, which were deposited under subaerial conditions. This fact shows that the topographical features of the fluvial deposits on the lower part of the great deltaic plains were formed after the Yayoi period. The minor regression is supposed to have taken place during the time from about 13th century to 19th century. The latter half of this period (Edo era, A. D. 1603-1867) constituted the most intensive delta-reclamation age in the history of Japan. In 20th century, the developed areas on the deltaic plains have suffered from many disasters. Among such disasters, those due to ground subsidence are of particular importance for their extensive area effected. This phenomenon is referred to as accelerated compaction of clayey stratum by lowering of underground water-level.
In the Early Pleistocene, the Tertiary fauna and flora had survived, and the Sino-Malayan elements migrated from the south to Japan through the southern land bridges. On the other hand, the first evidences of climatic deteriolation, such the northern temperate species as Pinus koraiensis and Picea Maximowiczii, appeared widely in the Japanese Islands. In the early Middle Pleistocene, the Japanese Islands might have been united with the continent by many land bridges. In the Middle to Late Pleistocene, the glacial eustatic changes of sea level left the marine sediments on the terraces along the coast of the Islands in the rising stage, while they dissected the land bridges in the stage of the lowered sea level. Through the above mentioned processes, the straits between the Islands and the continent had been formed at some parts of the land bridge, which had exerted an influence on the migration and distribution of the fauna, flora and the Man. Elephas naumanni migrated to Japan through the southwestern land bridge, which might have been still complete in the Middle Pleistocene. This migration route was broken by the end of this stage and this elephant disappeared in the early Late Pleistocene. But, in the Latest Pleistocene, Elephas naumanni reappeared in the Japanese Islands together with the cool temperate faunas and floras through a land bridge, which emerged above the lowered sea surface at the site of the former strait. In the Würm, the Earliest Man of the Japanese Islands, Homo sapiens, distributed widely and left a large number of palaeolithic implements, which are represented by blade, knife blade, point etc. (Table 1). Elephas naumanni became extinct by the end of the latest Würm.
Change of coast-line of the Japanese Islands during the Jomon Age, the neolithic age of Japan from 12, 000 to 2, 300 years B. P., is discussed mainly from archeological evidence, especially from shell mounds. Change of climate during the same age is also summarized from studies of plant remains and pollen analyses.
Environmental conservation from man-induced deterioration due to technological impact and urbanization is an urgent task in the presentday Japan. Contribution from Quaternary research should be expected to provide most essential data for the conservation of natural environment. The changes of environment, especially higher order changes, should not occur without close relation to the natural systems, even if the changes may cause due to man's impact. So that, comprehensive and historical understanding of natural environment consisting of physical, chemical and biological systems and their dynamics must be the foundation for the systematic analysis of spatial and sequential processes of environmental changes induced by man's impact. Standing on this point of view, the author discusses on the basic problems for studying environmental deterioration. As for deterioration resulting from urbanization, he suggests a framework of studying (Fig. 1). In this chart, complex land system is divided into five subsystems, i. e. rainfall-runoff, erosion-transportation-deposition, ground-earthquake motion, ground-groundwater, and surface morphology-wind subsystems, and relation of man-induced sequential changes of these subsystems to the occurrence of natural hazard is presented schematically. In conclusion, such future problems as spatial analysis and prediction of environmental changes which are necessary for the establishment of conservation systems are discussed briefly.