10:45 AM - 11:00 AM
[MIS12-07] Relationship between topography and decrease of wetland on the top of Mt. Naeba, Central Japan
Keywords:decrease of wetland, transition of vegetation, topography, Mt. Naeba
1. Background and Purpose
The mountaintop marsh of Mt. Naeba is home to numerous ponds and alpine plants, and has been selected as one of the 500 most important wetlands in Japan by the Ministry of the Environment, making it important from the perspective of biodiversity conservation. However, the mountaintop marsh is shrinking due to the decrease in snowfall caused by global warming in recent years. In addition, the vegetation formation process near the summit of Mt. Naeba was discussed, but there are few papers describing the formation process of mountain marshes, as opposed to lowland marshes. Therefore, the authors decided to investigate the relationship between vegetation succession and topography by aerial photo interpretation on three different times, topographic analysis using 5m mesh DEM taken by GSI, and field surveys, and to explore the factors behind the decrease in marsh area.
2. Method
In this study, aerial photo interpretation and field surveys were conducted to create a vegetation map of the Mt. Naeba summit marsh. Vegetation classification was performed using orthoimages of GSI maps from three periods: 1977, 2014, and 2019. Vegetation was divided into three types: marsh, bamboo grass, and forest. In 2024, a field survey using a GNSS receiver was conducted to measure the boundary between the marsh and the bamboo grass, and the expansion range of the bamboo grass from 2019 to 2024 was clarified. In addition, a topographic analysis (slope amount, slope direction, roughness) was performed using 5m mesh DEM taken by GSI. Vegetation changes were examined by overlaying the vegetation maps for each period on GIS. In addition, a survey of soil layer structures using soil probe and a survey of remaining snow distribution using satellite images were conducted, and the relationship between vegetation changes and these were overlaid and analyzed. From the above surveys and analyses, the factors behind vegetation changes were examined.
3. Results and Discussion
The vegetation change based on aerial photo interpretation showed that most areas remained unchanged, followed from bamboo grass to forest, from bamboo grass to marshland, and from marshland to forest, in that order, with an overall trend of increasing forest. About the vegetation change over the past five years, bamboo grass has noticeably invaded marshes at high altitudes, on southeast-facing mountaintop slopes (Fig.), in areas with relatively steep slopes, and in areas with high roughness. In the soil structure survey, it was found that the thicker the layer, the more moisture the soil retains, so the marsh is more likely to remain intact, while the thinner the layer, the easier it is for bamboo grass and forest to invade because it dries easily. As a result of focusing on the presence or absence of peats under the humus layer, it is thought that there are two patterns: one where bamboo grass and forest have invaded what was originally a marsh, and one where bamboo grass and forest were distributed there from the beginning. In the survey of remaining snow using the satellite PLANET, it was found that remaining snow is mostly found on the underside of convex areas and in snowdrifts, and is often seen in grassland, bamboo grass, and forest, but is rarely seen in wet marsh. It is thought that if the remaining snow continues to remain, meltwater will not reach the marsh, and it will become drier.
The mountaintop marsh of Mt. Naeba is home to numerous ponds and alpine plants, and has been selected as one of the 500 most important wetlands in Japan by the Ministry of the Environment, making it important from the perspective of biodiversity conservation. However, the mountaintop marsh is shrinking due to the decrease in snowfall caused by global warming in recent years. In addition, the vegetation formation process near the summit of Mt. Naeba was discussed, but there are few papers describing the formation process of mountain marshes, as opposed to lowland marshes. Therefore, the authors decided to investigate the relationship between vegetation succession and topography by aerial photo interpretation on three different times, topographic analysis using 5m mesh DEM taken by GSI, and field surveys, and to explore the factors behind the decrease in marsh area.
2. Method
In this study, aerial photo interpretation and field surveys were conducted to create a vegetation map of the Mt. Naeba summit marsh. Vegetation classification was performed using orthoimages of GSI maps from three periods: 1977, 2014, and 2019. Vegetation was divided into three types: marsh, bamboo grass, and forest. In 2024, a field survey using a GNSS receiver was conducted to measure the boundary between the marsh and the bamboo grass, and the expansion range of the bamboo grass from 2019 to 2024 was clarified. In addition, a topographic analysis (slope amount, slope direction, roughness) was performed using 5m mesh DEM taken by GSI. Vegetation changes were examined by overlaying the vegetation maps for each period on GIS. In addition, a survey of soil layer structures using soil probe and a survey of remaining snow distribution using satellite images were conducted, and the relationship between vegetation changes and these were overlaid and analyzed. From the above surveys and analyses, the factors behind vegetation changes were examined.
3. Results and Discussion
The vegetation change based on aerial photo interpretation showed that most areas remained unchanged, followed from bamboo grass to forest, from bamboo grass to marshland, and from marshland to forest, in that order, with an overall trend of increasing forest. About the vegetation change over the past five years, bamboo grass has noticeably invaded marshes at high altitudes, on southeast-facing mountaintop slopes (Fig.), in areas with relatively steep slopes, and in areas with high roughness. In the soil structure survey, it was found that the thicker the layer, the more moisture the soil retains, so the marsh is more likely to remain intact, while the thinner the layer, the easier it is for bamboo grass and forest to invade because it dries easily. As a result of focusing on the presence or absence of peats under the humus layer, it is thought that there are two patterns: one where bamboo grass and forest have invaded what was originally a marsh, and one where bamboo grass and forest were distributed there from the beginning. In the survey of remaining snow using the satellite PLANET, it was found that remaining snow is mostly found on the underside of convex areas and in snowdrifts, and is often seen in grassland, bamboo grass, and forest, but is rarely seen in wet marsh. It is thought that if the remaining snow continues to remain, meltwater will not reach the marsh, and it will become drier.