Rapid Landslide Mitigation Appraisal (RaLMA): A tool for appreciating the role of trees in slope stabilization

Landslides killing hundreds of people have become an almost yearly phenomenon in SE Asia and have a high profile in the public debate. High rainfall events on wet soil on hill slopes can trigger 'failure' in planes of weakness in the soil profile which leads to movement of soil. Forest vegetation and trees can play an important role in holding a
soil profile together through their root systems, and the removal of trees and subsequent decay of tree roots may be part of the explanation of specific landslides. Ironically, however, the risk of landslides after removal of trees is partially because the trees prevented landslides to happen earlier, and contributed to the build-up of soil until this is too heavy for the existing slope steepness. Landslides, or slope instability, can also be due to construction of roads and other structures that interfere with the flow paths of water through a hill-slope.