Vegetation Succession and Rate of Topsoil Development on Shallow Landslide Scars of Sedimentary Rock Slope Covered by Volcanic Ash and Pumice, Southern Kyushu, Japan

Abstract

In this study, vegetation succession and the rate of consequent topsoil development were investigated in shallow landslide scars of sedimentary rock slopes covered by volcanic ashes and pumice in Kagoshima prefecture, Japan. Seven shallow landslide scars of different ages were selected as study areas. In the initial period after the occurrence of a shallow landslide, deciduous broad-leaved trees such as Mallotus japonicus or Callicarpa mollis were occupied in the areas. Approximately 30 years after the landslide, evergreen broad-leaved trees such as Cinnamomum japonicum invaded in the areas, already existed present deciduous broad-leaved trees. After 50 years, the summit of the canopy comprised evergreen broad-leaved trees such as Castanopsis cuspidata var. sieboldii and Machilus thunbergii. Moreover, the diversity of vegetation invading the site reached the maximum after 15 years, followed by a decrease and stability in the number of trees. The total basal areas under vegetation increased with time. It was concluded that the vegetation community reaches the climax stage approximately 50 years after the occurrence of a shallow landslide in the study areas, in terms of the Fisher-Williams index of diversity () and the prevalence of evergreen broad-leaved trees. Moreover, according to the results of topsoil measurement in the study areas, the topsoil was formed at the rate of 0.31 cm/year. The development of topsoil usually functions to improve the multi-faceted functions of a forest. However, when the increased depth of topsoil exceeds the stability threshold, the conditions for a shallow landslide occurrence are satisfied. Therefore, we indicated to control the depth of topsoil and strengthen its resistance by forest management in order to restrain the occurrence of shallow landslides.

A Study of Disaster Prevention and Characteristics of Landslides Triggered by the 2019 Typhoon Mitag in Samcheok

“…즉, 산불 발생 후 지표면은 소수성 (Hydrophobia) 현상에 의한 침투율이 낮아지기 때문에 지표 류의 증가와 편중으로 인해 침식이 가속화될 뿐만 아니라 토양유실이 증가하여 산지미지형의 정단부와 상부곡벽사면 을 중심으로 황폐화 현상이 고착화된다 (Marques and Mora, 1998;Ma and Jeong, 2009;Park et al, 2009). 따라서 해당 미지형에서는 장기간에 걸쳐 토양의 수분 및 양분이 결핍되는 등 열악한 수목 생육환경이 유지되며 (Teramoto et al, 2016) Lee et al, 2004).…”