Detecting the onset of rangeland degradation using soil respiration and boundary lines: preliminary findings from the Nama Karoo

Abstract

Mean annual soil respiration correlates with net primary productivity and therefore provides an indication of ecosystem functioning. Soil respiration, however, varies considerably in space and time owing to the influence of factors such as soil nutrient content, temperature and water content. Comparing soil respiration across a fence-line separating rangelands in contrasting condition can potentially isolate effects of rangeland management from other abiotic variables. To explore this idea, soil respiration was measured from 260 different collars across a fence-line contrast in the Nama Karoo, near Beaufort West, over a period of four days in May 2005. Differences in soil respiration across the fence-line were only evident when the data were analysed in relation to soil temperature. The large data set enabled delineation of boundary lines relating soil respiration to temperature on the two farms. The boundary line analysis showed that constraint on soil respiration was between 0.2 and 0.4 umol CO2 m−2 s−1 greater under high compared to moderate stocking density. It was concluded that measurement of soil respiration is likely to be useful for detecting changes in ecosystem function as a result of over-utilisation of Karoo rangeland.