The ecological impact of abandoned Maasai setilements on savanna vegetation and its herbivores in the Amboseli ecosystem

Abstract

The open savannas scientist have come to regard as typical have been created by the activities of humans, livestock, fire and wildlife. Many studies of savannas ecosystems have concentrated on the fairly destructive effects of fire, waterholes and woodcutting. deemphasizing the human role. Yet human activity, especially pastoralism is an important part of the savanna ecosystem. In many parts of the world, savannas continues to expand as forest and woodland recede due to human activities including woodcutting for fuel and clearing new kind for cultivation. The impact of abandoned human settlements on the savanna ecosystems is of major importance, but is poorly understood. Construction of a settlement initiates alterations that, in some cases, could last for centuries. In particular, the soils of settlements develop different chemical and physical properties from the soils of undisturbed areas nearby. During the life of a settlement, cattle, sheep and goats forage on a large area, returning home every night. These animals continually deposit large amounts of nitrogen-loaded faeces and urine over a small area, boosting the availability of nutrients essential for plant growth and production, which are often in inadequate supply in savanna ecosystems. After a settlement has been abandoned, it may act as a source of nutrients far into the future. Essentially, abandoned settlements become eutrophic islands in a dystrophic area. In Amboseli, ground Gover on settlements that had been abandoned for less than 40 years was higher than on the surrounding areas. The settlements that had been abandoned for much longer periods tended ot have a canopy cover dominated by Acacia tottitis, which shades out most of the pioneer herbs and grasses that colonize settlement soon after abandonment. Different herbivores utilized abandoned settlements at successive vegetation stages. Soon after abandonement, some herbivere species spent time resting in the safe open areas of former settlements. Grazers took advantage of the abundant grass that succeeded the pioneer herbs and eventually A. tortilis attracted browsers to the abandoned settlements