Abstract:
Tropical semi-arid ecosystems are intricate ecosystems characterized by
alternating dry-wet cycles. The question of how trees and grasses coexist under a
considerable range of environmental and management conditions has been
referred to as the "savanna problem" The practical significance of understanding
the dynamics of natural ecosystems in relation to disturbances induced by
herbivory, changing land use patterns or climate change is increasingly being
recognized. Natural resource conservationists, range managers, and other
custodians of natural resources require concrete information bases for land use
policy formulations and as a means of regulating land use systems for sustainable
resource use and development. An experiment using a randomised complete
block design was set up to measure the effects of induced disturbances on
ecosystem components and concomitant plant physiological responses. Analysis of
variance techniques were used to determine the presence or absence of significant
treatment effects. Disturbed micro-sites (manipulated treatments where Acacia
tortilis trees were removed) demonstrated contrasting results compared to the
non-disturbed micro-sites (Acacia tortilis trees left intact).The disturbed sites had
less average moisture content in the 10cm soil profile (14.4%) than the nondisturbed
sites(18.8%). Panicum maximum had an average stomata conductance
of a magnitude of 0.65cms-1(270mmolm-2 s-1) for the disturbed microsites and
0.75cms-1(312mmolm-2s-1) for the non-disturbed sites. There were no significant
treatment effects in transpiration rates and leaf water potential of Panicum
maximum in the disturbed and non-disturbed sites. This analysis demonstrates
that long term changes in microenvironmental conditions of soil and plant water
status due to tree removal is likely to cause shifts in botanical composition of
graminoid species with direct implications on nitrogen sequestration, species
biodiversity, and productivity.
