Forage Diversity and Impact of Grazing Management System on Rangeland Ecosystems in Mbeere District, Kenya
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Date
2003-06
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Addis Ababa Universty
Abstract
Plant species composition, biomass, frequency and density of Mbeere rangeland has been
described to compare open and enclosed sites. A total of 245 plallf species were identified.
Clipping and preference unit technique were used to estimate herbaceous alld trees and
shrub biomass respectively. Density and callopy cover were done through counting and
visual estimation for three growth forms while forage preference was through direct
obsen'ation. Soil samples were analysed for soil moisture, pH, total nitrogen, organic
matter, exchangeable cations, percent carbon, available phosphorus, bulk density, soil
colour and textural class (sand, clay and silt content). The species sampled were classified
illfo twenty community types (ten each for herbaceous and all vascular plant species) using
Syntax. The effect of grazing and management system in this rangeland was studied both
on the vegetation and on the soil properties. Grazing reduces above ground biomass in
communal lands mainly through overgrazing and elimination of palatable species. Forage
productivity on the other hand largely depends on availability of rainfall and disturbance.
In the dry season the biomass accumulated was relatively low but substantially increased
during the wet season. Grazing management systems used in this particular rangeland
have a direct impact on forage diversity. T-test results sholVS that total species ric/lIless
and herbaceous richness in the open site were significantly differellf (p<O.05) from the
enclosed site. Species diversity alld evenness were higher in open than in enclosed sites.
Biomass and shrub cover were also significantly higher (p<O.05) ill enclosed site than in
the open site. Comparisons of life fomls dominance using ANOVA shows that
phanerophytes and therophytes were significantly differellf (p<O.05) from the rest of life
forms. The biomass of all plant life forms occurring in the dl)' season in the open site )Vas
significantly different from the others at (p<O.05). The life form spectrum of chamaephytes
and therophytes differed from the normal life form of Raunkiaer. An investigation of the
soil characteristic in grazed and IIngrazed sites showed dramatic differences in some soil
parameters. There were significant differences (p<O.05) ill pH, organic matter, percent
carbon, total nitrogen, moisture, bulk density and percellf clay between the enclosed plots
and open plots. Goats and cattle were observed to have complemellfary feeding habit
thereby reducing forage competition.
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Keywords
in Mbeere District, Kenya