花粉分析法による南樺太及び北海道の森林並に氣候の變遷に關する研究

Abstract

The present paper deals with the changes in the forests and the climate in Southern Saghalien and Hokkaido, studied by means of pollen analysis. The writer first made a thorough study of the recognized methods of pollen analysis, adopted by workers aboard, and then developed a new method by which have accurate results can be obtained. He carried out pollen analysis in many of the peat-bogs in Southern Saghalien and Hokkaido, and from the results attained was able to visualize the historical changes in the forests and the climate since the Diluvium epoch. The conclusions of this study are summarized in the following paragraphs: In 1930, when this study of pollen analysis was begun, there was in this country no adequate study of pollen grains. Consequently, the first step taken by the writer was to sketch and measure the pollen grains and spores of 172 kinds of plants found in and about the former Saghalien Experiment Station of Kyoto University. Next, he determined the significance of pollen analysis, as a means of determining the historical changes in the forests and the climate of Japan since the Diluvium epoch. Study was made of the usual methods of treating peat for extracting pollen grains, in conformity with the chemical consideration of the structure of the pollen-membrane of the components of peat. The writer pointed out some defects theoretically inevitable in these procedures, and finally devised a new method of treating peat. In brief, this new procedure corrects a major defect in the alkaline and dehydrated acetic acid methods, usually adopted for the treatment of peat, which do not take it into consideration the fact that the content ratio of the principal substances of peat, such as humic acid, lignine and cellulose, generally shows certain gradual changes from the upper strata of peat down to the lower ones. In addition, as regards the representation of the percentage of pollen grains, the writer improved upon the usual method and adopted the new procedure shown in the above illustrations. As the result of applying the new pollen analysis method to the peat from 17 different localities, the historical changes of forests in Southern Saghalien and Hokkaio since the Diluvium epoch can be summarized as follows: In the northern part of S. Saghalien, the forests of Picea › Abies accompanied by Larix were dominant in the Alluvium epoch, as at the present time, and there have been few changes in the composition of the forests since the beginning of that epoch. In the lower and upper parts of the Diluvium epoch, Picea and Abies decreased considerably and were replace by Betula; the resultant forests of Betula accompanied by Larix were then so predominant as to give a forest composition very different from the present one. In the southern part of S. Saghalien the forests of Picea ‹ Abies accompanied by Larix have been dominant through the Alluvium epoch up to the present time, except in its first period, when the construction of forests is presumed to have been of a kind very different, from the present. In the Alluvium epoch in Hokkaido, in and about the Ishikari Lowland, there was a dominance of Quercus-Alnus in its first period, but thenceforth up to the present time Quercus, Betula, and Abies have been dominant in this area. In and about the Kuromatsunai Lowland, Quercus, Alnus, and Fagus were the major forest components in the first period of the Alluvium epoch, but since that time Quercus, Betula, Abies, and Fagus, have been dominant in this area. In the upper Diluvium epoch in Hokkaio, in and about Hahoro, there existed a kind of forest such as can now be seen in the northern part of S. Saghalien, and about the Kuromatsunai Lowland the same kind of forest as now exists in the northern part of Hokkaido. In a period in the lower Diluvium epoch, in and about Kusiro, the dominant forests resembled those now found in the northern part of S. Saghalien, while in and about the Ishikari Lowland the forests resembling to the middle, if we can suppose any, between those in the southern part of S. Saghalien and those in the northern part of Hokkaido. In dealing with the changes in climate corresponding to those in the forests, the writer endeavored to acquire a more precise view by studying in detail the forest ecological nature and the changes, both past and present, of Picea jezoensis Carr, Abies sachalinensis Fr. Schm. and Larix dahurica Turcz. var. japonica Maxim., the three principal kinds of tree which constitute the present forests. It was indisputable that in the forests of Abies and Picea which characterize Southern Saghalien, Abies was more abundant in the southern part of the island and Picea in the northern part. But the transition in predominance of these two kinds of tree could not yet be fully explained. The writer's study established that these two typical forest types, which separate S. Saghalien into northern and southern areas, are divided by a line drawn from Maguntan on the east coast to Esutoru on the west coast. In Hokkaido proper, though Larix never grows naturally at the present time, the writer found a small amount of Larix pollen in each stratum of lignite equivalent to a period of the upper and the lower Diluvium epoch. Thus the writer can state that Larix once grew naturally in Hokkaido, and that the southern limit of its distribution then was between the Ishikari Lowland and the Kuromatsunai Lowland. After studying the changes in forest types from the various points of view, the writer offers the following explanation of the changes of climate which occurred in this region: In the Alluvium epoch, from its beginning up to the present time, the climate in the northern part of S. Saghalien has remained virtually unchanged, while that in the southern part of S. Saghalien and in Hokkaido was somewhat milder and warmer in the first period at the present time. Except for this first period of the Alluvium epoch, the Southern Part of S. Saghalien Climate has prevailed the present time in the southern part of S. Saghalien, as have the Southern Hokkaido Climate in and about the Ishikari Lowland, and the Northern Honshu Climate in and about the Kuromatsunai Lowland. Concerning the climate in the Diluvium epoch, the following conditions are noted. During a period of the lower and the upper Diluvium epoch, the present Northern Part of S. Saghalien Climate prevailed in and about Kusiro and Hahoro, where the Hokkaido Climate is now dominant. In and about the Ishikari Lowland, now situated at the southern extremity of the Hokkaido Climate Zone, a climate corresponding to that supposedly between the Southern Part of S. Saghalien Climate and the Hokkaido Climate was dominant in a period of the lower Diluvium epoch. In and about the Kuromatsunai Lowland, now situated on the border between the Northern Honshu Climate Zone and the Hokkaido Climate Zone, the Northern Hokkaido Climate was dominant in a period of the upper Diluvium epoch. The writer's study has pointed out the existence of a frigid period at least once in each of the upper and the lower Diluvium epochs in Hokkaido. The extent of its frigidity can be concluded to have been sufficient to lower the border line between the Northern and Southern Parts of S. Saghalien Climate, which corresponds nearly to the line drawn from Maguntan to Esutoru in S. Saghalien, southward to between Hahoro and the Kuromatsunai Lowland in the former case, and to between Kusiro and the Ishikari Lowland in the latter.