Abstract:
Invasive alien species are a leading cause of biodiversity loss in the world today. In
Kenya, Prosopis juliflora Linnaeus emend. Burkart is one of the most problematic
invasive plant species. The origins and pattern of introduction of Prosopis juliflora into
East Africa are not well known but large-scale introductions occurred in the 1980s.
Little information is available on how its innate characteristics interact with the local
habitat characteristics. Four hypotheses were tested to explain the effects of the invasion
of P. juliflora on soil nutrient status, diversity of indigenous plant species, diversity of
floral insect visitors of native Acacia spp., and how the invasive tree’s genetic diversity
would relate to the rate of invasion. Plant and soil sampling was carried using modified
Whittaker plots. P. juliflora density had significant influence on total organic carbon,
and pH. The invasive species also had a negative effect on overall native plant species
richness and density of Acacia species. This was a clear indication that P. juliflora is
having an effect on the species richness of local species and that either P. juliflora is
slowly replacing the indigenous Acacia species, or that the established stands of Acacia
in non-disturbed conditions are a good deterrent to the encroaching P. juliflora. The
results showed that P. juliflora is a preferred source of floral resources for A. mellifera
during the dry season. Allozyme analysis revealed minimal genetic distance between
populations. This study shows that the invasive species has negative consequences to the
local ecosystem at high densities.
Key words: Prosopis juliflora, Acacia species, species richness, soil properties,
pollinators, genetic diversity
