宮沢賢治作品の野火と山火 : イーハトヴの草原景観をつくった火入れと三年輪採

宮沢賢治(以下賢治と記す)は作品の中に、3つの山野の「火」を措いた。1つは主として草地に火が入れられる野火(prescribed fire or burning)である。野火の燃える描写は短歌や詩、童話「楢ノ木大学士の野宿」などにみられる。当時の岩手県、とくに北上山地には広大な採草地や放牧地が広がっていたが、この草地の重要な維持管理手法が火入れであった。童話「風の又三郎」はそのような草地を舞台としている。そこに登場したクリの樹幹は、同じ方向から繰り返し焼かれることによって、片側が著しく損傷している。この描写は、火入れ時の延焼動態(fire behavior)を表している。2つは、草地や焼畑の火入れから延焼したり、山作業時の不注意から出火したりして主として森林が燃える森林火災の山火(wild fire)である。詩「山火」や童話「よだかの星」などにみられ、山火も春期に多発したことが、作品から読み取ることができる。3つは、焼畑の火である。しかしながら、当時の岩手県で広く行われていた焼畑について、賢治はほとんど関心を払わず、わずかに文語詩の1篇に「焼畑」の語がみられる。盛岡高等農林学校において、賢治が学んだ当時の農学や生物学は、草地の生産と土壌の肥沃度や表層の安定にとって、このような草地への火入れが、負の効果しかもたないことを明らかにし始めていた。しかしながら、賢治が詩のなかで用いた造語「三年輪採」を発想した動機は、この科学的研究成果をうけて、連年の火入れを戒め、3年間隔の火入れを農民に推奨することにはなかった。「三年輪採」に相当する草地管理の起源は、藩政時代にあり、藩有林を火災から守りたい領主(為政者)と肥料や飼料を確保したい農民との間に結ばれた協定にあった。連年の火入れが草地の衰退の原因になることを領主と領民が理解していたことも、この協定の背景にある。そして、岩手県の各地で行われた3年間隔の草地への火入れを、古くからの春の風物詩であると賢治は捉えていた。In his works, Kenji Miyazawa described the following three types of "fires" as occurring frequently in the forest and grassland in Iwate Prefecture. The first type was a prescribed fire or a prescribed burning, which burned grasslands and pastures. Such vegetation was widely distributed in the Kitakami Mountains of the time when Kenji Miyazawa worked. This kind of grassland was semi-natural vegetation in Japan and was used in order to harvest feed and manure. The prescribed burning was usually performed there, in order to improve reproduction of grass or to control weeds and generating of trees. Kenji Miyazawa described this prescribed burning in Japanese poems of 31 syllables, in other poetry and in short novels. There were trees of Castanea crenata which were burned by prescribed burning in the grassland of the "Kaze no Matasaburoh" fairy tale. It was remarkable that the trunks of the trees burned and were severely damaged on only one side. Since these trunks were repeatedly burned from the same direction, this singular damage was formed. And his depiction of these trees expressed exactly the fire behavior of prescribed burning. The second type was a forest fire or a wild fire. This forest fire spread from prescribed burning, and happened because of people\u27s carelessness. Forest fires occurred frequently in the spring. The forest fires were found at "Yama-bi (forest fire)" in poems and "Yodaka no Hoshi" in fairy tales. The third type was a prescribed burning of shifting cultivation, which burned the vegetation of grassland and forest. However, Kenji Miyazawa had hardly been interested in the shifting cultivation that was widely performed in Iwate Prefecture at that time in the past. This type of fire was presented only in poems, described by literary language. Kenji Miyazawa learned agriculture and botany in the Morioka agriculture-and-forestry college. And he wrote many works based on the scientific literacy that he obtained in the process while he studied and researched those natural sciences. Therefore, it was thought that the knowledge of the science of those days was reflected in his work. Doubts about the effects of prescribed burning for maintaining grassland and of prescribed burning to raise the fertility of the soil were raised by the agricultural and ecological research of the time. "San-nen Rinsai," which was a poetic word that Kenji Miyazawa coined, meant prescribed burning at a three-year interval. And it was thought that the result of research in the above-mentioned sciences was reflected in his coined word. However, this hypothesis was not borne out, and the origin of "San-nen Rinsai" was traced to the agreement between the feudal lord and farmer about the prescribed burning of grassland. He had recognized these prescribed burnings, as they were a true symbol of the spring season of his native land "Iwate.