Trees and Crops Arrangement in the Agroforestry System Based on Slope Units to Control Landslide Reactivation on Volcanic Foot Slopes in Java, Indonesia

Rina Purwaningsih,Muhammad Anggri Setiawan,Junun Sartohadi

doi:10.3390/land9090327

Abstract

Agroforestry, as the dominant land use at the volcanic foot slope in Java Island, is prone to landslide due to a combination of rough relief and thick soil layer. However, evaluations of specific vegetation patterns against landslide reactivation due to soil erosion, which relays on the existing slope units and geomorphological processes, are still limited. The research data were collected through aerial photo interpretation by delineating morphological units of old landslides, slope units, and the existing land use. This was followed by field surveys for two consecutive purposes, i.e., (1) verification of aerial photo interpretation and (2) identification and intensity assessment of existing geomorphological processes. The data were tabulated according to slope units, as a basis for tree and crop arrangement in controlling erosion and landslide, by considering economic, social, and ecological functions. The agroforestry would control the landslides reactivation if the tree and crop arrangement was based on the morphological units formed by the previous landslide. The slope units are classified into residual zones at the highest elevations with flat slopes, erosion zones with the steepest slope, and sedimentation zones at the lowest elevations with gentle slopes. Trees and crops at those three units of the former landslide have different functions in controlling processes of rill erosion, gully erosion, and soil creep.

Highlights

Landslides that occur at the volcanic foot slope and thick soil, especially in Java, leave a mark in the form of typical surface morphology
The residual zone is dominated by rill erosion and cracks, the erosional zone is dominated by gully erosion, cracks, landslide reactivation, and material displacement, and the depositional zone is dominated by gully erosion, landslide reactivation, and soil creep
In the agroforestry area, rill erosion and landslide reactivation lie along the erosional and depositional zone, while gully erosion and landslide reactivation are scattered on the depositional zone

Summary

Introduction

Landslides that occur at the volcanic foot slope and thick soil, especially in Java, leave a mark in the form of typical surface morphology. The results of soil redistribution by landslides can be observed in three slope zones from the highest elevation to the lowest elevation, namely residual, erosion, and deposition [6,7,8]. Volcanic ash deposition, which results from eruption processes during the volcanic body formation period, forms a very thick soil at the volcanic foot slope zone. Very thick soils combined with the high elevation, and the steep slope angles make the volcanic foot slope prone to landslides. The volcanic foot slope has a great potential for agricultural sector development, especially in the former landslide area, where the soils have favorable characteristics to support plant growth [8]

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