Main Article Content
Fire and the dynamics of semi-arid grassland: influence on plant survival, productivity and water-use efficiency
Abstract
There is a lack of knowledge concerning the effect of fire behaviour on
the vegetation dynamics of semi-arid climates. Arising from this, an investigation
was initiated to characterise the behaviour of fires burning with the
wind (head fire) and against the wind (back fire). The behaviour of these
fires was related to the response of the vegetation by monitoring the
recovery and productivity of the grass sward after only one burn over
a two year period (2000/01 to 2001/02 seasons). The results showed that
head fires had significantly greater flame height and rate of spread than
back fires. However, at ground level back fires were more intense and
had a negative effect on recovery of the grasses, resulting in lower litter,
yield and water-use efficiency (aboveground phytomass or crude protein
produced per unit of evapotranspiration). Fire had a significant effect
on plant density and cover, with basal cover 68% lower than that of unburnt
grassland two months after the fire. Cymbopogon plurinodis with
large tufts had the most die-back of all the species. With the exception
of plant cover and density, which takes longer to recover, it takes approximately
two complete growing seasons to recover from most of the detrimental effects
of fire. The initial increased crude protein content of the plant material
caused by fire did not off set the approximately 50% reduction in plant
production the first growing season after the fire. Fire significantly
decreased WUE (water-use efficiency), with an average over the two growing
seasons of 3.06kg ha-1 mm-1
and 2.45kg ha-1 mm-1 for unburnt and burnt grassland respectively. In
various semi-arid grassland areas, the use of fire as a management tool
is questionable if there is no specific purpose for it.
Keywords: back and head fires; basal cover; crude protein content; grass sward recovery; tuft mortality
African Journal of Range & Forage Science 2003, 20(1): 29–39
the vegetation dynamics of semi-arid climates. Arising from this, an investigation
was initiated to characterise the behaviour of fires burning with the
wind (head fire) and against the wind (back fire). The behaviour of these
fires was related to the response of the vegetation by monitoring the
recovery and productivity of the grass sward after only one burn over
a two year period (2000/01 to 2001/02 seasons). The results showed that
head fires had significantly greater flame height and rate of spread than
back fires. However, at ground level back fires were more intense and
had a negative effect on recovery of the grasses, resulting in lower litter,
yield and water-use efficiency (aboveground phytomass or crude protein
produced per unit of evapotranspiration). Fire had a significant effect
on plant density and cover, with basal cover 68% lower than that of unburnt
grassland two months after the fire. Cymbopogon plurinodis with
large tufts had the most die-back of all the species. With the exception
of plant cover and density, which takes longer to recover, it takes approximately
two complete growing seasons to recover from most of the detrimental effects
of fire. The initial increased crude protein content of the plant material
caused by fire did not off set the approximately 50% reduction in plant
production the first growing season after the fire. Fire significantly
decreased WUE (water-use efficiency), with an average over the two growing
seasons of 3.06kg ha-1 mm-1
and 2.45kg ha-1 mm-1 for unburnt and burnt grassland respectively. In
various semi-arid grassland areas, the use of fire as a management tool
is questionable if there is no specific purpose for it.
Keywords: back and head fires; basal cover; crude protein content; grass sward recovery; tuft mortality
African Journal of Range & Forage Science 2003, 20(1): 29–39
