Short-term response in productivity following an unplanned fire in a semi-arid rangeland of South Africa

摘要

During the dormant winter period the semi-arid rangeland areas of South Africa are characterized by unplanned fires, either by lightning or negligence by man. The quantification of the impact of burning in terms of the above- and below-ground phytomass production, rain-use efficiency (RUE), crude protein, root/shoot ratios and plant density of the grass sward was conducted in a semi-arid rangeland over 2 years (2000/2001-2001/2002 growing seasons) following an accidental fire. Fire (head fire) had a significant (p<0.01) influence on plant density. Grass species with larger tufts (Cymbopogon plurinodis and Themeda triandra) suffered the most dieback due to the fire. The initial advantage in quality (crude protein) accompanying the fire does not neutralize the reduction in half of above-ground phytomass production and poor (p<0.01) RUE occurring in the first season following the fire. Burnt rangeland takes at least two full growing seasons to recover in terms of above- and below-ground phytomass production, litter and RUE. Fire lowered (p<0.01) RUE for both growing seasons especially during the first four months. The average RUE was 3.72 and 2.86 kg ha~(-1) mm~(-1), respectively, for unburnt and burnt rangeland for the 2 years. Root mass decreased (p<0.01) by 59% over the first 100 mm depth due to fire. More than 80% of the root mass was found in the top 0-300 mm soil layer. The below-ground growth is more sensitive to burning than above-ground growth. Fire reduced the root/shoot ratio from 1.44 to 1.30. These results can serve as scientific guidelines in claims for damages and short-term risk management of semi-arid rangeland after an accidental runaway fire driven by August winds.