4:30 PM - 4:45 PM
[HGG01-05] Geographical implications of disturbed forest and degraded landscape from historical and present perspectives in Japan
Keywords:defunctionalized forest (hageyama), degraded landscape, landslide, economic value, satoyama
Japanese mountain forests were most intensively disturbed in the period from the end of Edo to the middle of Meiji eras. From the end of the Meiji era to the post WWII, overuse of mountain forest resources occurred extensively, causing disturbance of mountain slopes and resulted in frequent landslides and floods. Especially in the Tokai and Chugoku regions, growth of population during the modern era (17th century onward) caused expansion of disturbed mountain forests (i.e. bare mountains) especially in granite areas. Chiba (1956) called them as ’hageyama’ with its definition that is ‘forests that have lost their normal functions’, so that we here call them ‘defunctionalized forests’. Field data suggest that defunctionalized forests (hageyama) also appeared on granite mountains in the Tohoku region during the modern era. Indeed, we have found at present landslide sites on granite mountains in the Chugoku and Tohoku regions evidence showing that regolith materials supplied and accumulated in the modern era (most probably when defunctionalized forests dominated mountain slopes in the areas) have the significant influence on the present landslides.
On the other hand, after intensive afforestation during the post WWII, Japanese forests have long faced a paucity of maintenance works due to multiple reasons, including an increase in inexpensive imported timbers, a decline in domestic timber prices, and insufficiency of human resources who sustain the forest industry. Consequently, trees have not been harvested, resulting in the situation that Japanese forests have never been richer and wider in history. Presently in 2017, plantation forests occupy 45% of the Japanese forests and the paucity of maintenance work of the plantation forests has caused an increase in tree density, which has led to a decline of the economic value of the timber, changes in pleasant landscape of satoyama. This situation is widely recognized as ‘degradation’ of the forest. However, in a geomorphological perspective, evidence has not been clearly presented for showing the increase in landslides as tree density increases. Studies rather suggest that forest maintenance work, that often promotes construction of mountain roads, inevitably disturb soil layers which should have negative impacts on slope stability. Kadomura (1991) focused on the Japanese climatic environment under which climax vegetation will be forest, and defined ‘degraded landscapes’ in Japan as a landscape where forest is not easily restored. In this definition, plantation forest is not recognized as ‘degraded landscape’, regardless of its quality.
Forests are presumably an environment that includes not only trees but also, at least, soil layers. Some people recognize degradation of forest based on the economic value of timbers or the cultural value of the scenery of satoyama. But others, such as Chiba and Kadomura, would see degradation at the scale of landscape that represents the functions or system of the forest environment. Geography may have an advantage to study ‘degradation’ of mountain forests, because, ‘degradation’ occurs spatially and temporally in combination of human intervention and physical processes.
Chiba T, 1956. A research on Hageyama. The Agriculture and Forestry Association, Tokyo, 237pp.
Kadomura H, 1991. Introduction to Degraded Landscape Stuides. In: Degraded Landscapes in Japan (ed. Kadomura H.), Report of Grant-in-Aid for Co-Operative Research, 5-32.
On the other hand, after intensive afforestation during the post WWII, Japanese forests have long faced a paucity of maintenance works due to multiple reasons, including an increase in inexpensive imported timbers, a decline in domestic timber prices, and insufficiency of human resources who sustain the forest industry. Consequently, trees have not been harvested, resulting in the situation that Japanese forests have never been richer and wider in history. Presently in 2017, plantation forests occupy 45% of the Japanese forests and the paucity of maintenance work of the plantation forests has caused an increase in tree density, which has led to a decline of the economic value of the timber, changes in pleasant landscape of satoyama. This situation is widely recognized as ‘degradation’ of the forest. However, in a geomorphological perspective, evidence has not been clearly presented for showing the increase in landslides as tree density increases. Studies rather suggest that forest maintenance work, that often promotes construction of mountain roads, inevitably disturb soil layers which should have negative impacts on slope stability. Kadomura (1991) focused on the Japanese climatic environment under which climax vegetation will be forest, and defined ‘degraded landscapes’ in Japan as a landscape where forest is not easily restored. In this definition, plantation forest is not recognized as ‘degraded landscape’, regardless of its quality.
Forests are presumably an environment that includes not only trees but also, at least, soil layers. Some people recognize degradation of forest based on the economic value of timbers or the cultural value of the scenery of satoyama. But others, such as Chiba and Kadomura, would see degradation at the scale of landscape that represents the functions or system of the forest environment. Geography may have an advantage to study ‘degradation’ of mountain forests, because, ‘degradation’ occurs spatially and temporally in combination of human intervention and physical processes.
Chiba T, 1956. A research on Hageyama. The Agriculture and Forestry Association, Tokyo, 237pp.
Kadomura H, 1991. Introduction to Degraded Landscape Stuides. In: Degraded Landscapes in Japan (ed. Kadomura H.), Report of Grant-in-Aid for Co-Operative Research, 5-32.