K. Z. Mganga

Competition indices of three perennial grasses used to rehabilitate degraded semi-arid rangelands in Kenya

Rangeland degradation is one of the most serious environmental challenges in arid and semi-arid environments in Africa. Grass reseeding technology, using indigenous perennial grass species has a great potential for restoring ecosystem functionality in these degraded lands. This study was aimed at investigating how the establishment of indigenous grasses used to rehabilitate degraded semi-arid rangelands in Kenya as monocultures or binary mixtures affect dry matter biomass yields and plant competition indices at different phenological stages of development: seedling, elongation and reproduction. Using plant competition indices, we demonstrated which among these grass species showed a complementary vis-a-vis competitive interaction in binary mixtures across their phenological stages. Monocultures and binary mixtures of three perennial grass species: Cenchrus ciliaris L. (Buffel grass), Enteropogon macrostachyus Munro ex Benth. (Bush ryegrass) and Eragrostis superba Peyr. (Wilman lovegrass) native to these semi-arid rangelands were established in a field experiment. Pure stands of E. macrostachyus yielded higher biomass than C. ciliaris and E. superba only at the seedling and elongation phases but not the reproduction phase, where the yields were lowest among pure stands. Negative plant interactions in binary mixtures were observed at seedling and reproduction stages, compared with positive interactions observed at the elongation phase. Binary grass mixtures had a significant advantage for exploiting available environmental resources only at the elongation phase but not at the seedling and reproduction phases. Based on the estimated competition indices, E. superba best complements C. ciliaris across the phenological stages. We therefore conclude that this binary mixture is the one most likely to ensure successful rehabilitation of degraded semi-arid rangelands in this region.

Determinants and rates of land degradation: Application of stationary time-series model to data from a semi-arid environment in Kenya

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.