The effect of different fire regimes on plant diversity in southern African grasslands

Summary

Study 1

Fire may be an important component in managing grasslands for grazing mammals and maintaining grassland diversity. However, the effects of fire in southern African grasslands are poorly understood. In this study, the effects of long-term burning treatments on biodiversity in mesic grassland was investigated.

Study site: The effects of long-term burning treatments on  mesic grassland was investigated at the University of Natal research farm, Ukulinga (840 m.a.s.l.), 8 km south-east of the town of Pietermaritzburg.

Burn treatments: Plant diversity was examined under a range of burning treatments in a randomly allocated, replicated block design. The treatments were:

1) biennial (i.e. two years between fires) and triennial autumn burns;

2) annual, biennial and triennial winter burns;

3) annual, biennial and triennial spring burns;

4) no-burn.

Each treatment was replicated in three 14 m x 18 m plots for 48 years. During burning, a back burn was lit on the down wind side of the plot and a head burn lit on the opposite side. The head burn was carried across the plot by the prevailing wind, until it met the back burn.

Sampling: The importance-score method was used to sample plant diversity, providing estimates of species richness and abundance. A series of concentric nested sub-quadrats (1, 2, 5, 10, 20, 50 and 100 m²) were used, measuring from the smallest to largest sub-quadrat size. Each plant species was awarded a score depending on the first sub-quadrat in which it was encountered. Thus, the first encounter of a common species should be in the smaller sub-quadrats (the 1 m² quadrat holding a score of 7), whereas of a rare species in the larger quadrats (the 100 m² quadrat holding a score of 1). Average species richness was calculated for each treatment for the 1 and 100 m² quadrats.

Species richness showed no consistent, clear responses to frequency or season of burning. Comparing species compositions, no-burn treatments had different communities to burn treatments, with more woody species being present. When no-burn was removed from the analysis, the communities separated out according to block and not burning regime. Also, the sod-forming grasses Aristida junciformis, Cymbopogon excavatus and Tristachya leucothrix decreased with increasing fire frequency, whereas the bunch grasses Themeda triandra and Diheteropogon amplectens increased with increasing fire frequency.

 

Study 2

Fire may be an important component in managing grasslands for livestock grazing and maintaining grassland diversity. However, the effects of fire in southern African grasslands are poorly understood. In this study, the effects of long-term burning treatments on biodiversity in moist montane grassland was investigated.

Study site: The effects of long-term burning treatments on biodiversity in moist montane grassland was investigated at Cathedral Peak (1,890 m.a.s.l) in the Mlambonja Wilderness Area of the Drakensberg mountain range, KwaZulu/Natal (South Africa).

Burn treatments: Plant biodiversity was examined under a range of burning treatments in a randomly allocated, replicated block design. The treatments were:

1) biennial (i.e. two years between fires) summer burn;

2) annual and biennial autumn burns;

3) annual and biennial winter burns;

4) annual, biennial, and quinquennial spring burns;

5) no-burn (control).

Each treatment was replicated in three, 25 m x 25 m plots for 19 years. During burning, a back burn was lit on the down wind side of the plot and a head burn lit on the opposite side. The head burn was carried across the plot by the prevailing wind, until it met the back burn.

Sampling: The importance-score method was used to sample biodiversity, providing estimates of species richness and abundance. A series of concentric nested sub-quadrats (1, 2, 5, 10, 20, 50 and 100 m²) were used, measuring from the smallest to largest sub-quadrat size. Each plant species was awarded a score depending on the first sub-quadrat in which it was encountered. Thus, the first encounter of a common species should be in the smaller sub-quadrats (the 1 m² quadrat holding a score of 7), whereas of a rare species in the larger quadrats (the 100 m² quadrat holding a score of 1). Average species richness was calculated for each treatment for the 1 and 100 m² quadrats.

Species richness suggests that plant diversity in southern African montane grasslands is highest with biennial autumn or winter burns. Species richness in 1 m² quadrats decreased with longer intervals between spring burns, but there was no relationship between frequency of spring burns and species richness in 100 m² quadrats.

Comparing species compositions, no-burn treatments had different communities to burn treatments, with more woody species being present. When no-burn was removed from the analysis, the communities separated out according to block and not burning regime. Also, the sod-forming grasses Harpochloa falx and Tristachya leucothrix decreased with increasing fire frequency, whereas the bunch grasses Themeda triandra and Koeleria capensis increased with increasing fire frequency.

 

Study 3

Fire may be an important component in managing grasslands for grazing mammals and maintaining grassland diversity. However, the effects of fire in southern African grasslands are poorly understood. In this study, the effects of long-term burning treatments on biodiversity in semi-arid grassland in South Africa was investigated.

Study site: The effects of long-term burning treatments on biodiversity in semi-arid grassland was investigated at Honeydale (550 m.a.s.l), the University of Fort Hare’s research farm, located 5 km east of the town of Alice (Eastern Cape).

Burn treatments: Plant diversity was examined under a range of burning treatments in a randomly allocated, replicated block design. The treatments were:

1) annual, biennial (i.e. two years between fires), triennial, quadennial winter burns;

2) annual, biennial, triennial and quadennial spring burns;

3) no-burn.

Each treatment was replicated in two 10 m x 10 m plots for 26 years. During burning, a back burn was lit on the down wind side of the plot and a head burn lit on the opposite side. The head burn was carried across the plot by the prevailing wind, until it met the back burn.

Sampling: The importance-score method was used to sample biodiversity, providing estimates of species richness and abundance. A series of concentric nested sub-quadrats (1, 2, 5, 10, 20, 50 and 100 m²) were used, measuring from the smallest to largest sub-quadrat size. Each plant species was awarded a score depending on the first sub-quadrat in which it was encountered. Thus, the first encounter of a common species should be in the smaller sub-quadrats (the 1 m² quadrat holding a score of 7) whereas of a rare species in the larger quadrats (the 100 m² quadrat holding a score of 1). Average species richness was calculated for each treatment for the 1 and 100 m² quadrats.

Species richness suggests that there is a small increase in diversity in southern African semi-arid grasslands with decreasing burn frequency. Comparing species compositions, no-burn treatments had different communities to burn treatments, with more woody species being present. When no-burn was removed from the analysis, the communities separated out according to block and the no burning regime. Also, the sod-forming grass Cymbopogon plurinodis decreased with increasing fire frequency, whereas the bunch grass Themeda triandra increased with increasing fire frequency.


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