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University of Nairobi (2003)

The impact of land use changes on vegetation, soil and animal distribution in Kajiado and Makueni Districts, Kenya

Mworia, John K

Titre : The impact of land use changes on vegetation, soil and animal distribution in Kajiado and Makueni Districts, Kenya

Auteur : Mworia, John K

Université de soutenance  : University of Nairobi

Grade  : Doctor of Philosophy PhD 2003

In the last 2 decades the semi-arid areas of South Kenya have undergone rapid land use changes characterized by group ranch sub-division, intensification of cUltivation and increased human settlement. The aim of this study was to quantify the influence of key land use types on vegetation comp ?sition, structure and production. Secondly to study the influence of land use types, vegetation types and key environmental gradients on wildlife distribution, composition and habitat preference. The study was conducted between November 1998 and April 2001 in the southeastern districts of Kajiado and Makueni. The land use types studied were conservation, group ranch, individual ranches and small scale mixed farms. To identify the impacts of land use on vegetation the effects of environmental gradients were first separated. The main environmental gradient identified using Principal Component Analysis (PCA) was chemical base richness as indicated by available K, Ca, Mg, Na and soil pH. Soil physical variables especially texture contributed the highest variation on the 2nd gradient. The vegetation of the study area was charaterised by Acacia species which had the highest overall density and Balanites aegypitiaca with the highest importance value. Classification using TWINSPAN separated 7 tree species associations. Gradients in tree composition were extracted using Detrended Correspondence Analysis (DCA). The primary gradient charaterised by increasing Commiphora species and decreasing Acacia drepanolobium was most strongly correlated to base richness and soil pH. The 2nd compositional gradient was most strongly correlated to soil texture variation. Small mixed farms followed by communal areas showed the highest impact of selective wood harvesting leading to a shift in structure and composition. This was manifested by a lower percentage of basal area, wood biomass and density/ha of matu e trees as compared to similar associations in the conservation and individual ranches. Herbaceous biomass was significantly lower in the communal and mixed farms as compared to the conservation and individual ranches. The problem of invasive plants especially species of Astripomea and Ipomea was widespread with an exception of the conservation areas. Excluding grazing through exclosures led to significant decline in invasive species biomass and increase in grass biomass. Permanent water points influenced herbaceous biomass with a 23% decline within a radius of 4km. Soil moisture, a factor thought to influence grass to wood balance varied with land use, vegetation type and proximity to water sources. Moisture availability in the soil increased with increasing ratio of grass cover in the wood to grass balance. The effect of proximity to watering points varied with livestock density in the land use type. Wildlife biomass comprised 16% of the animal biomass. The communal Kiboko Group Ranch and Chyulu Conservation Area had significantly higher wildlife density than individual ranches, mixed farms and Kiboko Range Research Station. Wildlife predominantly utilized the lowland Maasai ranches in the wet season and Chyulu CA in the dry season. The degree to which land use and environmental factors influenced wildlife distribution varied with season. Gradient analysis showed grass biomass and proximity to seasonal water ponds to be the most important factors in the dry and wet seasons respectively. Boma density and cultivation intensity remained secondarily important factors in both seasons. Analysis of habitat preference showed strong spatial separation of wildlife species in the dry season based on feeding categories and body size. Livestock density and composition varied with land use type. The grazing patterns varied with season with Chyulu CA and KRRS playing the role of dry season reserve grazing. The importance of herd mobility and interdependence of land use types was particularly evident in the 1999/2000 drought when 80% of the cattle in the study area was.move

Mots clés : Land use / Vegetation / Soils / Kajiado District,Kenya / Makueni District, Kenya

Présentation (Research Kenya)

Page publiée le 22 septembre 2010, mise à jour le 3 avril 2018