david kiama

Shadetolerance and regeneration of some heavily exploited timber species(Uvariopsis congensis, Antiaris toxicaria, Funtumia africana,Prunus africana and Aningeria altissima)were studied in two adjacent sites in Kakamega tropical rain forest. The twosites have been subjected to different logging intensities. Within one of thesites, relatively intact areas were compared with adjoining more disturbedones.Seedling presence or absence in mature forest phase, sapling proportions in gapand the mature phase and diameter distributions were used to classify thespecies into shade tolerance groups. Results indicate that except forUvariopsis, the species are non-pioneer lightdemanders and could fit into three shade tolerance groups: A groupresembling pioneers but with seedling in shade, a mid-tolerant group andone showing a high shade tolerance. Amount of regeneration and disturbance wererelated: regeneration being higher in the more disturbed site except forUvariopsis. The intersite differences...

Shadetolerance and regeneration of some heavily exploited timber species(Uvariopsis congensis, Antiaris toxicaria, Funtumia africana,Prunus africana and Aningeria altissima)were studied in two adjacent sites in Kakamega tropical rain forest. The twosites have been subjected to different logging intensities. Within one of thesites, relatively intact areas were compared with adjoining more disturbedones.Seedling presence or absence in mature forest phase, sapling proportions in

One of the land degradation hotspots in the Kenyan Rangelands is Suswa.  Intense gully formation in the area has led to severe land degradation, loss of livestock and human life, destruction of infrastructure including the Maai-Mahiu-Narok Road and heavy siltation in Lakes Magadi and Natron threatening flamingo breeding sites and increasing production cost of soda-ash. This degradation has not always been there and studies show the gullies absent in 1988.

The study objectives were to identify and map land degradation hotspots in the Suswa/Lake Magadi Basin in order to help concentrate land rehabilitation efforts where most needed and also give recommendations on how to combat the degradation.

The study used soil erosion risk based on the revised universal soil loss equation model, trends in land-use/land-cover, trends in livestock density, trends in human population density, presence/absence of soil conservation structures in hilly cultivated areas and presence/absence of gullies as indicators to map the land degradation hotspots.

The main degradation factor in the most humid, higher altitude parts of the study area (parts of Kinale, Njabini and Narok East, rainfall 1000 mm -1200 mm) is cultivation on steep hills with minimal soil conservation structures and sand harvesting especially along roads with exposed subsoil. The cultivation in unsuitable areas is driven by a five-fold increase in human population density in Kijabe area and a ten-fold increase in Narok East area between 1979 and 1999. However, the soils in this region have low to medium erodibility which has prevented severe gully formation.
The area around Suswa and Mai-Mahiu had the highest density of gullies. The main degradation factors in this drier (500 mm – 750 mm rainfall), lower lying area are extremely weak soil structure especially in the sub-soil making them susceptible to a rare type of soil erosion called tunnel erosion where tunnels form underground leading to collapse of soil surface and severe gully formation, high livestock densities leading to overgrazing, crop cultivation in an area only marginally suited to crop growing, increased human population and location. The Suswa area is surrounded by hills and ridges which drain a lot of water into the location. Expansion of cropland in this area is supported by data with results showing an exponential increase in acreage (14, 000 acres to 47, 000 acres) under cultivation between 1990 and 2018. The study results also show high livestock densities in the Suwa area with cattle, sheep and goat populations increasing sharply from 1970s to the 2000s. The increased cultivation and livestock population growth could be attributed to an explosive (>1500 %) human population increase in the area through birth and immigration between 1979 and 1999. Good ley crops of Rhodes grass (Chloris gayana) have been established in the area and increased open grasslands at the expense of Acacia drepanolobium wooded grassland around Akira area probably reflects this.
Degradation factors in the driest part of the study area south of Suswa towards Lake Magadi include charcoal production, overgrazing, gully formation, wind erosion, aridity and salinization/alkalization. Although human population growth was least in this region, it still increased by 175.4% between 1979 and 1999. Acacia tortilis is the most targeted species for charcoal production. This activity is converting Acacia tortilis woodlands into open grasslands or shrubbed grasslands.  Cutting for fencing is another major activity contributing to loss of woody vegetation in the area with the Acacias the most targeted. Some areas around Nachu, some areas between Nachu and Ol-tepesi and some areas south of Ol Orian were the most affected. However, tree cover of Commiphora, Delonix elata, Combretum, Balanites aegyptica, Acacia seyal, Sterculia, Boscia angustifolia had increased on ridges east of Ol-tepesi (Oldonyo-Loruka Hills), ridges south east of the study area around Esonorua and Karero areas. There was also increased forest cover in Kijabe area and Suswa Hills. Woody cover had also increased on ridges along the eastern boundary of the study area and especially around Lorngosua but the dominant species in some of these areas were Commiphora, not highly targeted for charcoal production. Soil erodibility was lowest in this region because of the stony surfaces (from past volcanic action) in many places, and gully formation is not as intense as in the Suswa area.  Sheep and goat populations in the area increased throughout the 1970s, 1980s, 1990s and 2000s but cattle density was highest in the 1980s, then decreased. Decreased cattle density reflects increasing aridity and decreasing grass cover. Aridity may combine with overgrazing and salinization to cause low herbaceous cover and bare areas observed in some parts of the region.
It is recommended that the county governments in the study area implement both the national and county governments’ legislation on water and soil conservation. To do this will require prioritization of environmental conservation and awareness creation on sustainable land management through extension officers, local radio stations, churches and barazzas. Explosive human population growth in the area is the main underlying cause of the land degradation. It is recommended that family planning campaigns be intensified in the area using vernacular radio stations popular in the area. Gullies should be rehabilitated through establishment of soil and water conservation structures and appropriate grass, tree and shrub species planted. Suitable species in the Suswa-Mai-Mahiu area include Star grass (Cynodon plectostachyus), Acacia drepanolobium and Dodonaea angustifolia. In the higher, more humid areas, road banks can be stabilized by planting Kikuyu grass (Pennisetum clandestinum) and farmlands insured against soil erosion through Fanya Juu/Fanya Chini contour terraces stabilized by suitable grass species. South of Suswa, the many volcanic rocks found on the surface can be used to rehabilitate the gullies and to fence off degraded areas to allow for natural regeneration or planting with suitable shrub/tree species. Improved livestock marketing through establishment of disease free zones to enable access to overseas markets can help reduce overstocking. Greater uptake of energy saving jikos and alternative fuel sources in urban areas can help reduce cutting of trees for charcoal production.

Landslide is a form of soil erosion that results from a downward and outward movement of slope-forming materials including rocks, soils, and artificial fills. Landslides are among the major natural disasters in mountainous regions of Kenya with Murang’a County having the highest number of recorded incidences of landslides. Negative impacts of landslides include soil erosion, land degradation, loss of land value, loss of life, loss of property, destruction of infrastructure including roads and bridges, displacement of people, boundary conflicts, and siltation of rivers. Landslides occurrence is closely related to rainfall, land slope, land cover, soil type and geology. Major landslide triggers include heavy continuous rainfall in soils with infiltration rates greater than internal drainage, deforestation of steep slopes, slope instability caused by man-made cuts in hills during road construction or excavation of toe-slope and gullies.

While some studies on factors influencing landslide occurrence in Murang’a County have been carried out, few if any had tried to map landslide risk prior to this study. A landslide risk map allows easy identification of areas most susceptible to landslide for mitigation measures to be put in place to reduce the negative impacts of landslides.

Empirical models using parameters like rainfall, land-cover, slope, soil type, geology and distances from roads have frequently been used to assess landslide occurrence risk. The study integrated a soil erosion vulnerability map and landslide occurrence data to come up with a landslide risk map.  The soil erosion vulnerability map was based on the universal soil loss equation model with inputs being vegetation index expressed as normalized difference vegetation index (NDVI), rainfall erositivity, slope factor (length and angle), soil erodibility and socio-economic factor (human and livestock population).

High landslide risk areas were found in the steep, high rainfall (>1880 mm), densely populated tea/dairy zone on the slopes of Aberdare Ranges. Moderate landslide risk areas were mainly found in the coffee/tea and main coffee zones, with steep to moderate slopes and an annual rainfall of between 1200 mm to 1800 mm. Some hilly areas on the eastern part of the county with annual rainfall of around1000 mm also had moderate landslide risk because of steep slopes. Low landslide risk areas were found in the flatter low lying and lower rainfall areas of the county. An unexpected landslide trigger was burst water pipes with up-to thirty percent of landslides in some areas caused by burst water pipes. It is recommended that landslide risk mapping be extended to other counties at high risk of landslides. Mitigation measures against landslides such as gabions along roads in hilly areas and soil conservation measures should be enhanced. Burst water pipes should be promptly repaired to prevent soil water saturation leading to landslides. Degraded areas should be rehabilitated through tree planting