Land-use and land-use change effects on nitrous oxide emissions in the seasonally dry ecosystems of Zimbabwe: A review

Abstract

Nitrous oxide (N2O) is a greenhouse gas (GHG) with a considerable warming potential and involvement in the destruction of stratospheric ozone. The conversion of savannas to agricultural land has the potential of changing the characteristics and gas exchange of the ecosystems dramatically. The savanna woodlands cover over 95% of Zimbabwe’s forest area, and are divided into five woodland types: Acacia, miombo, mopane, teak (Baikiaea Plurijuga) and Terminalia-Combretaceae. This review is aimed at exploring the effects of land-use changes and land management practices on N2O emissions in Zimbabwe. Available data on N2O emission were collected from standing and deforested miombo woodlands, grasslands and agricultural lands. Estimated mean annual N2O emissions from savanna ecosystems in Zimbabwe were 17.1 Gg N2O, while annual fluxes from arable land (cultivated and fallow) was 3.19 Gg N2O. Biogenic N2O emissions were mainly concentrated in the wet season as N2O production is strongly enhanced by high soil moisture. During the dry season pyrogenic emissions were also important sources of N2O, contributing, an estimated 6.7 Gg N2O annually. Land use change in the form of biomass burning and conversion to grassland or arable land may be considerable source of N2O, whereas current agricultural practices do not seem to provide a large source of N2O in Zimbabwe. Seasonally dry savanna ecosystems, thus, constitute an important source of N2O, which should not be ignored in national and regional estimates of emissions of N2O. Land-use change from savanna to agricultural production results in an immediate increase in N2O emissions. However, the emissions will decrease with time. The current estimates are associated with large uncertainties, thus, there is need for more detailed studies on the effects of land-use change on N2O emissions and on spatial and temporal variations in N2O emissions from the different savanna ecosystems.