森林立地55(1), 18 2013

Jpn J For Environ 55 (1), 1-8, 2013

 

炭化片分析により証拠づけられた奥田光山域における明治期の山火事

 

石田泰成1・逢沢1・大久達弘1

1宇都宮大学科学科

 

栃木県奥光山域において,治期の1905に撮影された山火事跡の古写真がデジタルアーカイブスとして公開されている。研究は,この写真の撮影地点の探査と樹構造の調査から,山火事が生した林分定し,そこで炭化片分析を行うことで,同分析によって山火事生が実証可か検討した。その上で,山火事生に関する献記のない山域の1915の古い地形図上にみられる広域的なササ地が,山火事によって成したものであるかを炭化析によってらかにすることを的とした。査の結果,山火事林分定することができた。山火事林分は,1915の湯ノ湖周の地形図ではササ地となっている場所と,その近くの広であった。また,献および樹構造の調査,この場所では120(1890)に山火事が生したこと,この周囲のカンバおよびミズナラの樹120以下であることがわかった。この林分での炭化片分析の結果,いずれの林分においても炭化が検出され,同分析によって,山火事生の実証が可と考えられた。次に,1915にササ地であったのミズナラ・シラカンバにおいて同様の調査を行った結果,すべての地点から炭化が検出され,樹は最大で101であった。以上から,奥光山域では治期に広域的な山火事が生しており,1915地形図のササ地およびその周囲の広にみられる現在の森植生は山火事後に成したものと推察された。

キーワード:光,治期,炭化片分析,山火事,ササ地

 

Yasunari Ishida, Mineaki Aizawa and Tatsuhiro Ohkubo : Evidence of forest fires in the Meiji era in the moun­tainous region of Nikko on the basis of charcoal particle analysis. Japanese Journal of Forest Environment 55:1-8, 2013.

In this study, we aimed to obtain evidence of forest fires that had occurred in the mountainous region of Nikko, Tochigi, by using an analysis for detecting charcoal particles on the soil surface of Sasa grasslands on a historical topographic map drawn in 1915, in which there were no historical documents of forest fire. To test the efficacy of the charcoal particle analysis, we first conducted the analysis in places where forest fires had occurred in the past; we located these places by using old photographs of burnt forests, taken in 1905 in the Meiji era; literature survey for forest fires; and surveys for tree age structure. We found that these places are situated in the Sasa grasslands and the adjacent broad-leaved forest near the Yu-no-ko Lake on the map in 1915. The literature survey showed that the forest fires had occurred near these places about 120 years ago (1890s); this information corresponded with the tree age structure of birch and oak forests around these places that consisted of trees less than 120 years of age. Charcoal analysis used in these forests detected charcoal particles in all the forests, indicating the efficacy of the analysis. Then, charcoal particle analysis and surveys in other oak-white birch forests in the area where the Sasa grasslands were located in 1915 revealed the presence of charcoal particles in all the forests, and tree age structure showed that the forests consisted of trees that were, at most, 101 years of age. Therefore, we collected evidence that forest fires had occurred across the region in the Meiji era and that the existing forest vegetation on the Sasa grasslands and adjacent broad-leaved forests would have been established after the fires.

Keywords : mountainous region of Nikko, Meiji era, charcoal particle analysis, forest fire, Sasa grassland


 
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