International Association for Promoting Geoethics (IAPG) - Official Blog

Deforestation and landslide hazard in Malawi: 
a geoethical perspective

by Annie Sylverio Jere

Annie Sylverio Jere

(Geologist at Akatswiri Mineral Resources, IAPG member, Malawi; email: jere.annie@gmail.com)

Picture above: 

2016 landslides induced by rainfalls in Chiweta, Rumphi districts. Landslides have blocked the road (source: http://www.faceofmalawi.com)

Trees have a fundamental role in the conservation of the environment by averting potential natural disasters. Through the absorption of harmful gases, trees save us from dangers resulting from the imbalance of carbon dioxide, sulfur dioxide, nitrogen dioxide occurring in the earth’s atmosphere (Nail, 2008). Moreover, as well known in the agricultural knowledge, trees prevent soil erosion. However, not often mentioned is also the role that trees play in preventing landslides.

Landslides are defined as the downward and outward movement of slope-forming materials under the influence of gravity, and in most cases water is equally involved (Varnes, 1978). Landslides description depends on the nature of their occurrence, they are sometimes called slides/slumps, avalanches, rockfall, and flows (Msilimba, 2007 & Varnes, 1978). Landslides of greater magnitude are mainly associated with failure of slope during earthquakes or rainfalls. The destabilization of materials (rock and soil) forming a slope, changes in water concentration levels and loss of woody vegetation may also trigger landslides (Broadhead and Forbes, 2011). Logging, trail construction, and forest conversion are some of activities that increase erosion and slope instability.

The roots of forestry vegetation help stabilize hill slopes by reinforcing soil shear strength (Abe and Ziemer, 1991).   Deep rooted trees and shrubs have the ability to reinforce shallow soil layers, anchor soil to bedrock, and form buttresses that resist soil movement, making shallow rapidly moving landslides less likely to occur (Broadhead and Forbes, 2011 & FAO and PECOFTC, 2013). Soil moisture levels are also reduced by the forest cover and undergrowth vegetation. This entails that landslides can be minimized or entirely averted though their main cause is natural.

In Malawi, landslides are prevalent in all the three country regions (Msilimba and Holmes, 2010). Quite a number of landslides have been documented in various papers. Most of these landslides are induced by continual heavy rains. Deforestation, which is being driven by rising demand for agricultural land, biomass energy (firewood and charcoal), timber and settlement purposes, is also considered among the main causes for the occurrence of landslides.

In the year 1946, Zomba experienced devastating landslides and floods which affected the Zomba plateau (the second largest mountain in Malawi), due to the heavy rains that fell continuously lasting for a number of days (Edwards, 1948). Landslides coincided with floods that claimed lives of many people, destroyed villages, homes and farms. Until now they are considered as the most catastrophic landslides and floods ever occurred in the district. Because of the destruction they caused, locals called those landslides and floods "Napolo" (a serpent that came to destroy many lives).

Rapid deforestation of sloping hills is attributed to economic activities such as, agricultural practices, logging, mining, development of residential areas, tourism (Broadhead and Forbes, 2011). These activities are the necessary catalysts to induce slope failure since the vegetational roots that are supposed to provide stability to the soil are destroyed (Bischetti et al., 2009). The recent deforestation in the Zomba Mountain has increased tremendously following the rapid growth of population. Trees are also being cut down for timber and the creation of space for farming and settlements. The inconsiderate deforestation of the mountain may result in the occurrence of landslides in the near future if no proper action is taken. Removal of forests from sloping land surely increase landslide risks. Even after the forestal regeneration, high landslide hazard remains, since the rooting strength may take up to two decades to recover to previous levels (FAO and PECOFTC, 2013).

Zomba Mountain, with the extent of deforestation,
and part of Zomba City

The removal of forest or brush cover and the replacement with grass or crops has often been found to substantially increase the susceptibility of hill slopes to landslides (Glade, 1998). Forests are also significant as they also serve as an effective barrier against rock, debris and soil falls from higher elevations, as well as to diminish the distance of the landslide run-out (FAO and PECOFTC, 2013). Grasses, which have shallow roots, take up most of the land when all trees have been cut down, as a result the slope becomes susceptible to the instability (Broadhead and Forbes, 2011).

The foot of Zomba Mountain hosts a city that in the future will be likely affected by even more deadly and devastating landslides than in the past. The occurrence of landslides may also damage the drainage systems, destroy riparian vegetation, induce soil erosion, accelerate the land degradation of the hill slopes, and reduce the scenic beauty of the mountain (Msilimba, 2007). Even though important policies have been implemented, Zomba population should be sensitized more on the importance of preserving trees in the mountain. Energy Statistics Database (1990) showed that more than 60% households in Malawi use firewood and charcoal for cooking (Broadhead, 2016). So, developing alternative sources of energy will contribute to prevent deforestation and reduce the landslide hazard, with positive repercussions on the protection of the natural environment and the safety of population.

References

Abe K. and Ziemer R.R. (1991). Effect of Tree Roots on Shallow-Seated Landslide. Proceedings, Geomorphic Hazard in Managed Forests. XIV IUFRO World Congress, 5-11 August 1990, Montreal, Canada, USDA  Forest Service Gen. Tech. Report PSW-130, Berkeley, California.

Bischetti G.B., Chiaradia E.A., Epis T., Morlotti, E. (2009). Root cohesion of forest species in the Italian Alps. Plant Soil (Impress), Doi: 10.1007/s11104-009-9941-0.

Broadhead J. & Forbes K. (2011). Forests and landslides: The role of Trees and Forests in the Prevention of Landslides and Rehabilitation of Landslide-Affected Areas in Asia. FAO, Bangkok.

Broadhead J. (2016). Nation al statistics Related to Woodfuel Production and Consumption Developing Countries, Survey-Based Woodfuel Studies, and International Recommendations on Woodfuel Surveys. Technical Report Series GO-17-2016.

Edwards T.A.C. (1948). Zomba Floods, December, 1946; Extracted from The Nyasaland Journal, 1.

FAO & The Centre for People and Forests (RECOFTC) (2013). Forest and Natural Disaster Risk Reduction in Asia and the Pacific. Brief Policy.

Glade T. (1998). Establishing the Frequency and Magnitude of Landslide-Triggering Rainstorm Events in New Zealand. Environmental Geology, 35.

Holmes P.J. & Msilimba G.G. (2010). Landslides in the Rumphi District of Northern Malawi: Characteristics and Mechanisms of Generation. Nat Hazards. Doi:10.1007/s11069009-9495.

Msilimba G.G. (2007). A Comparative Study of Landslides and Geo hazard Mitigation in Northern and Central Malawi: Thesis Submitted for the Doctor of Philosophy Degree,        Faculty of Agricultural and Natural Sciences, Department of Geography, University of    the Free State.

Nail S. (2008). Forest Policies and Social Change in England. Springer Science and Business Media. World Forest, Vol. 6.

Varnes D.J. (1978). Slope Movement Types and Proccesses, Landslides-Analysis and Control in Schuster R.L and Krizek R.J., National Research Council. Washington D.C. Transportation Research Board. Special Report 176.