Short-term response of rangeland following an unplanned fire in terms of soil characteristics in a semi-arid climate of South Africa

Abstract

Unplanned fires are a natural phenomenon in southern African rangelands. The influence of fire on soil characteristics (soil-water content, soil compaction, soil temperature, infiltration ability, soil properties especially organic matter, pH, exchangeable Ca, Mg, K, Na and extractable P) of a semi-arid rangeland was therefore quantified over two growing seasons (2000/01–2001/02) following an accidental fire. The decrease ( p⩽0.01) in basal cover due to fire (head fires) exposed the soil more to the natural elements and therefore to higher ( p⩽0.01) soil temperatures and soil compaction in turn leading to lower ( p⩽0.01) soil-water content and a decline in soil infiltrability. Two growing seasons after the fire, the decrease or disturbance in soil characteristics has still not been lifted. An increase in soil temperature of as much as 9°C on top of the soil surface occurred during the first year following the fire. One growing season following the fire, the highest soil temperatures (50 mm depth) for the burnt and unburnt rangeland were 39°C and 34°C, respectively, and occurred during December. Only 4 months after the fire, the soil-water content (0–300 mm depth) was already 31% lower due to the fire and 61% lower at the end of the first growing season. Over the first 0–50 mm soil layer, fire reduced ( p⩾0.01) organic carbon (C) and total nitrogen (N) content (as measures of organic matter content) and extractable P, but increased ( p⩽0.01) the pH and concentration of exchangeable Ca, Mg, Na and K in the soil. With depth, organic matter and K decreased and Ca increased ( p⩽0.01) between surface (0–50 mm) and lower (50–100 mm) layers due to burning. Accidental or unplanned fires contribute towards the so-called man-made droughts, while also influencing the short-term sustainability of the rangeland ecosystem.