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RECENT incidents of mass movement and large-scale soil erosion such as the Batang Kali landslide, the excessive water-and-sediment flow at Kg Iboi in Baling, and an earlier one in the vicinity of Gunung Jerai, remind us of the inappropriate and unscientific approach adopted when opening and preparing land for large-scale projects.
When the existing vegetation on a piece of land is felled and removed, the soil on the surface is exposed to erosion.
If no appropriate control measures are taken, the erosion process will, over time, wash away the top layer of soil, exposing the lower layer, or subsoil, which is likely to be much less stable than the surface layer.
Although such exposure may only cause minor soil erosion in the short term, it remains vulnerable to future unwanted incidents of soil movement during extremely wet spells.
Also, its capacity to retain water has been compromised. It becomes a factor that contributes to large-scale flooding.
Hillsides are protected by nature with trees of different species growing together, each with a network of roots. In normal conditions, tree roots, decaying leaf litter, and billions of microbes actively interact and facilitate various soil processes.
Both the soil and the slope are supported and stabilised by a strong and resilient network of roots.
Excessive disturbance and removal of any component of this system go against the laws of nature.
Any attempt to use and exploit the trees or the land should have been moderated by, at least, following conservation guidelines already developed by various authorities.
Projects should be planned according to the tolerance level of the various components (trees, soil, and microbial population).
Yet, for a long time, land on hill slopes has been exploited for various economic activities, including agriculture, housing, and infrastructure development without adequate protective measures.
Yet, although their integrity has been compromised, soils have remained largely intact. Even if such disasters are few and rather infrequent, it is still advisable to take normal soil conservation measures seriously.
Any extreme rainfall conditions, which seem to occur more frequently these days, will increase the vulnerability of the soil on slopes. For regions that frequently experience floods, a long-term re-vegetation programme in the hinterlands should be initiated now.
The positive effects may not be seen in the immediate future, but scientific evidence has shown that increased tree cover will certainly help to moderate flooding in later years and reduce the amount of sediment carried downstream.
The increased frequency and magnitude of such land-related disasters should serve as a reminder that we are not treating our natural resources with adequate care and respect. – The Vibes, January 4, 2023
Ghulam M. Hashim is a former soil scientist with the Malaysian Agricultural Research and Development Institute, a past president of the Malaysian Society of Soil Science, and author of two books and several book chapters on soil science
