Mechanisms of vegetation restoration at landslides caused by a catastrophic earthquake in Central Taiwan

Abstract

The vegetation restoration of a large-scale landslide, triggered by the catastrophic earthquake on 21 September 1999, in Jiujiu Peaks, Central Taiwan with an impacted area of 821 ha recovered 80% by 2020 was studied using self-organizing map (SOM) coupled with multi-temporal SPOT satellite images and a terrain-based distribution index for a 20-year period. Although disturbed by several typhoons during two decades of natural vegetation succession, the landslide restoration rate has reached 87.5% with the invasion or regrowth of vegetation gradually. A predicted logarithmic model with statistically significant difference was derived to estimate the restoration trend of the landslide in the studied area. Most of the poorly vegetated areas are located along the ridgelines, as verified by field surveys. Landslide restoration was carried out in three stages, (1) vulnerable landslides and fast-growing invasive vegetation (1999/9 - 2005/9); (2) stabilized landslides and slow-growing vegetation toward the vegetated strips (2005/9 - 2009/11); and (3) more stabilized landslides and vegetation toward secondary forest (2009/11–2020/2). Topographic location, water supply, typhoon disturbance, invasive or residual vegetation patterns and succession time are the main factors of landslide restoration. The evaluated results indicate that nature itself is a complex ecological balance system with a strong capacity for vegetation recovery at landslides, and can be used by government agencies to add in the recovery of landslide areas.