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The impact of fire (head and back fires) on the seasonal change in above-and belowground production in grass species, was quantified over two growing seasons (2000/01 and 2001/02) for semi-arid grassland. The behaviour of the head and back fires was also identified. Roots were extracted to a depth of 900mm with 50mm intervals, using a core and then separated from the soil by wet sieving and flotation. Sampling of both above- and below-ground phytomass, took place at approximately bi-monthly intervals to account for major seasonal changes. The intensity of the back fire was higher than the head fire at ground level. Most of the grass roots were found in the first 150mm soil layer. While fire increased grass root distribution over the first 100mm depth, it was decreased deeper in the soil. Root mass in semi-arid grassland is strongly seasonal, with the most active growth during the months of March and April when aboveground parts are dormant. Both above-and belowground phytomass production decreased significantly over the first year following burning. The above- and beIowground phytomass (900mm depth) was respectively 806kg ha-1 and 2 002kg ha-1 less due to burning, over the first year after burning. The seasonal root/shoot ratios for the unburnt and burnt grassland ranged between 1.62 to 2.80 and 1.20 to 3.12 respectively. It seems that root mass exceeds aboveground biomass for this semi-arid grassland. Over the short-term, fire decreased productivity and could subsequently influence the sustainable fodder production of a semi-arid grassland ecosystem. [ABSTRACT FROM AUTHOR]

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 50mm was 7°C. After only two months the soil-water content over the first 900mm 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. [ABSTRACT FROM AUTHOR]

During the dormant winter period the semi-arid grassland areas of South Africa are characterised by planned and unplanned fires, either by lightning or negligence by man. The influence of burning (head and back fire) on the germinability of grass species in the soil seed bank was quantified in the greenhouse over the 2000/01 to 2001/02 growing seasons for a semi-arid grassland. The behaviour of the head and back fires was also monitored. Soil seed bank samples were collected immediately after burning and then every third month over a two-year period from O.25m2 blocks 50mm deep. The same was done on unburnt grassland. At ground level, the back fire exceeded 100°C, while the head fire had temperatures of less than 100°C. The fire caused a flush of seedlings from the seed bank over the first season after the fire. The head fire stimulated seedling density significantly (P ≤ 0.01) more than the back fire. The mean (head and back fire) seed bank density the first season following the fire, for burnt and unburnt grassland, was respectively 84.6 and 52.1 grass seedlings m-2 for September, 50.5 and 21.9 grass seedlings m-2 for December and 347 and 58 grass seedlings m-2 for March. The pioneer species Aristida con gesta and Tragus koelerioldes only occurred in the soil seed bank of the burnt grassland, while the climax species Cymbopogon plurinodes, Digitaria eriantha and Panicum stapfianum only germinated in the unburnt grassland seed bank. The Era grostis species showed the highest germination due to fire. The burning of semi-arid grassland did have a quantified impact on the soil seed bank over the short-term. [ABSTRACT FROM AUTHOR]

The influence of burning (head and back fire) on seedling recruitment and survival of different grass species in a semi-arid grassland were quantified over the 2000/01 to 2001/02 growing seasons. The behaviour of the head and back fires was also monitored. Soil temperature and soil-water content were recorded once a week at 10mm and 50mm depth intervals respectively. At ground level, the back fire exceeded 100B0C, while the head fire recorded temperatures of less than 100B0C. Due to the lower basal cover (28% lower than for unburnt grassland over the first year after the fire) of the burnt grassland, the soil temperature, daily and seasonal to a depth of 50mm, increased (P < 0.05) while the soil-water content decreased (P < 0.05). The seedling survival was significantly lower due to the fire, which can possibly be ascribed to the lower basal cover and resultant change in micro-climate. The average seedling density of the surviving seedlings in burnt (average of head and back fires) and unburnt grassland at the end of the first season after burning, were 0.48 and 0.86 seedlings m-2 respectively. Fire influenced the species richness negatively. Pioneer grass species (Aristida congesta and Tragus koelerioide) intruded in the burnt grassland, which were not present in the unburnt grassland. The seedling establishment of Eragrostis chloromelas, Themeda triandra and Elionurus muticus were heavily decreased by fire. Eragrostis chloromelas was the species forming most seed culms per tuft over the growing season regardless of burning, with Elionurus muticus most stimulated for seed formation due to the fire, and Themeda triandra not much influenced by fire. The burning of semi-arid grassland did have an important impact on the seasonal survival of seedlings over the short-term, and therefore the resultant functioning of the grassland ecosystem. [ABSTRACT FROM AUTHOR]