International Journal of Molecular Evolution and Biodiversity 2016, Vol. 6, No. 2, 1-6
4
of regenerating tree population is declining. Many factors could have contributed to this decline of species diversity
in the study area, some of the possible factors include but not limited to competitive exclusion and low level of
disturbance (Whittaker, 1975; Connell, 1978; Huston, 1979; Peterson and Reich, 2008). Connell (1978) and Huston
(1979) studies provide linkages between disturbance frequency and species diversity. It appears that in the study
area
A. zanzibarica
is a competitive dominant species over the other species. Being nitrogen fixer, absence of
medium-sized browsers (Prins and Van der Jeugd, 1993), seed dispersal mechanism, reduction of hot fires, grazing
history and presence of heavy loamy-clay soils (Cochard and Edwards, 2011) are some of competitive advantages
of
A. zanzibarica
in the study area. Many studies have shown positive correlations between terrestrial animal and
plant diversity (MacArthur and MacArthur, 1961; Murdoch et al., 1972; Willson, 1974). This implies that reduction
in plant species diversity in the study area will have a negative influence on the animal’s species diversity simply
because plants provide different habitat types, food and other key resources (Lawton, 1994).
Figure 2 Relative density of regenerating and old trees' populations
Figure 3 Variation in Shannon Diversity Indices between trees with CBH ≥20cm (old tree population) and trees with CBH < 20cm
(regenerating tree population)
Note: F
1,18
8.146, P < 0.01
5 Management Implications
Maintenance of species diversity is one of the prime objectives of establishing protected areas network and the main
responsibility of wildlife managers. Despite the fact that our study had a limited coverage, we have managed to
show empirically that
A. zanzibarica
dominates and tree species diversity decline significantly in the study area.
A.
zanzibarica
is an indigenous tree species in Saadani National park which seems to be competitive dominant species
over other species and which has now extended to areas which historically were grasslands. We therefore propose
immediate measures to be taken to curb and reverse this vegetation transformation. This study recommends efficient
