LEAF STOMATA CONDUCTANCE, LEAF WATER POTENTIAL AND SOIL WATER STATUS IN PANICUM MAXIMUM (JACQ.) IN DISTURBED AND NON-DISTURBED MICROSITES IN A SEMI-ARID ECOSYSTEM IN KENYA

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.