Influence of fire on litter production and root and litter turnover in a semi-arid grassland of South Africa

Changes in litter production following back and head fires, some soil characteristics and root and litter turnover were quantified over two growing seasons for a semi-arid grassland. Sampling of litter production took place at approximately bi-monthly intervals to account for major seasonal changes over the 2000/01 and 2001/02 seasons. Soil compaction was determined by a simple rod penetrometer, soil temperature by mercury thermometers and soil-water content by a neutron hydroprobe. Litterfall of 5.88% and 1.13% (as a proportion of annual aboveground phytomass production) for unburnt and burnt grassland, respectively, was obtained. Two seasons following the fire, litter was still 47% lower due to fire. The litter production was not significantly different between the head and back fires. The fire, while causing a lower plant cover over the two years following burning, also significantly increased soil compaction and soil temperature. The biggest difference in soil temperature between burnt and unburnt grassland to a depth of 50 mm was 7 °C. After only two months the soil-water content over the first 900 mm depth decreased by 23% due to burning. Fire lengthened the period for replacement of the total root system by about a year and decomposition of litter by three months. Small changes caused by fire to the fragile ecosystems of semi-arid climates may have long-lasting consequences. The overall effects of fire on belowground systems and the resulting processes that feed back to aboveground systems are complex.