Plant ecological studies related to restoration of a degraded ecosystem in central Tanzania

Abstract: Kondoa Irangi area is among the most degraded ecosystems in Central Tanzania as a result of heavygrazing, fire, collection of fuelwood and improper cultivation practices. The restoration process of thisdegraded ecosystem through natural regeneration is slowed by the semi-arid climate of the area combinedwith poor soil nutrient status. Studies of population ecology of Acacia seyal and Brachystegia spiciformiswere conducted with and without protection against fire, grazing/browsing by animals and humandisturbance. The floristic and structural diversity of a remnant Afromontane forest was described. Inaddition, facilitation of regeneration in the study area through soil amendment, seeding and seedlingintroduction were also performed. The purpose of these studies was to obtain information that can beused for ecological restoration of the area as well as conservation of the remaining fragments of thenatural vegetation.For both Acacia seyal and Brachystegia spiciformis population densities, recruitment rates,seedling survival and population growth rates were generally higher in the protected than in theunprotected plots. The overall and stage-specific mortality rates of both species were usually higher in theunprotected than in the protected plots. The differences in vital rates between the two types ofenvironment suggest that beside climatic factors that cause temporal variation, tire, grazing and humaninfluence the plant population dynamics in the area.Soil amendments to facilitate regeneration showed that direct addition of seeds and planting ofseedling, particularly, of drought resistant species can be applied to increase recruitment and speciesdiversity and to promote regeneration. Nitrogen and other mineral deficiencies in the soil can becorrected naturally by, for example, addition of mulch and establishment of leguminous plants rather than by inorganic fertilization.In the Afromontane forest, timber species had declining populations, indicating the effect ofselective logging, while other species showed expanding or interrupted populations. A proposal toconserve this forest under a community-based forest conservation scheme is put forward. Based on thesestudies it can be concluded that the restoration of this degraded ecosystem is possible if disturbance doesnot exceed the present levels.