Water relations strategies of two grass and shrub species as influenced by prescribed burning in a semiarid ecosystem in Kenya.

Abstract

Burning of vegetation is common in most Kenya rangelands and has been done since time immemorial. However, little is known of the effects of burning on soil and plant water status. To investigate these effects, measurement of soil water potential, atmospheric variables, and xylem tension, transpiration rate and diffusive resistance of Acac ia mellifera, Commiphora riparia, Digitaria macroblephara, and Chloris roxburghiana were taken from burned and unburned plots at the National Range Research Station, Kiboko, during 1982-83. Results showed that burning had minimal effect on plant water status of the' four species. Most significant differences observed were numerically small and perhaps not biologically meaningful.Few large significant differences were observed but the cause for the differences was unknown. Burning did not significantly influence soil water status.Transpiration rates of the plants in the burned and in the unburned plots were observed to be primarily affected by atmospheric variables when soil water potential was favorable. On the other hand, xylem tensions of the plant species varied in response to variation of the soil water potential within a season.It was concluded that there was little or no competition for use of soil water among the plant species. The four species seemed to avoid competi tion among one another through different avoidance mechanisms such as variation in leaf size, leaf shedding, and different root biomass and distribution characteristics.