Fire alone, and in combination with grazing, influence established individual plants, and their
respective regeneration potential variously with consequences on species dynamics. This study
gives attention to the effects of fire alone, and in combination with grazing in underutilized,
problem rangeland communities. Firstly, the question exists whether annual fire in fire
prone Hyparrhenia hirta dominated veld could be one of the factors that promote the
persistence of this veld type in the Gauteng Highveld. Secondly, the impacts of fire and heavy
grazing on species and associated changes in veld condition characteristics are documented in
Cymbopogon validus dominated veld in the Eastern Cape.
The grazing value of Hyparrhenia hirta dominated rangelands is often managed through
frequent burning aimed at encouraging palatable re-growth. Despite this widely adopted
practice, research on the effects of fire on H. hirta seed production (seed banks) and seed
dynamics and therefore its regeneration potential, is lacking in South Africa. This study
quantified and compared H. hirta soil seed bank density, and seedling emergence in the field in
an annually burned site versus a > 2 year fire return interval site. It was hypothesized that H.
hirta seed bank densities and seedling emergence would be greater in annually burned veld
compared to > 2 year fire return interval veld. The seedling emergence method was used to
determine seed bank densities of soil samples collected from the two sites. Seedling emergence
was quantified and monitored under individual treatments within burn (clipping, soil
disturbance, control) and unburned sites (soil disturbance, litter, clipping, and control) over a single growing season. Results revealed that H. hirta seed bank densities were nearly two fold
higher in the annually burned site but not significantly so. In the seedling emergence trial, no
consistent trend was identified in individual treatments but emergence was generally favored
in control plots (associated with standing vegetation), and reduced in clipped plots (associated
with a short sward). However, analysis of the pooled data (annually burned site versus > 2 year
fire return interval site) revealed a significant increase (p<0.0001) in emergence in the annually
burned site. It was concluded that frequent burning of H. hirta dominated stands may be one of
the factors that facilitates its dominance, through increasing seed additions to the seed bank.
This is likely the case where H. hirta is underutilized after burning, therefore allowing seed to
set and encouraging its availability in the seed bank. Furthermore, underutilization
inadvertently results in burning in subsequent years with accumulative effects on the soil seed
bank, and subsequent emergence patterns.
In the high rainfall, sourveld grasslands of the Eastern Cape, the eradication of underutilized
stands of Cymbopogon validus has been directed through burning and intensive grazing on the
farm Glen Gregor, outside Bedford. At this study site, species composition of standing
vegetation, basal cover, tuft diameter and standing biomass were sampled in top and bottom
slopes of five camps representing a gradient of fire and grazing management intensity.
Additionally, the composition of the soil seed bank was determined through the seedling
emergence method from soil collected from the same sites. Results showed that the success of
C. validus eradication was not determined by burning alone, as burning without the required
post fire grazing maintained a dominance of C. validus. Cymbopogon validus decreased along
the grazing gradient according to the total number of seasons that a camp was grazed after
burning. Heterogenous topography in camps with steep top slopes and gentle bottom slopes
meant grazing was concentrated in bottom areas, reflected by significant reductions of C.
validus compared to top slopes. In contrast, even utilization in camps of uniform topography
reduced the prevalence of C. validus over the whole camp, reflected by similar frequencies in
top and bottom slopes. Cymbopogon validus dominated sites were associated with large areas
of bare ground between large tufted individuals. In contrast, C. validus eradication through fire
and intensive grazing went hand in hand with the occupation of large bare spaces by other species, predominantly Sporobolus africanus, Cynodon dactylon and other subclimax species
which lead to increases in basal cover. Cymbopogon validus was increasingly absent from the
seed bank as its frequency was reduced in the sward. The presence of other species in the seed
bank, regardless of C. validus dominance could indicate a highly functional role of the seed bank
in this mesic environment. It is proposed that once established (as C. validus is suppressed) it is
these individuals that will provide the source of additional seed for subsequent population
establishment. Windows of opportunity for establishment are facilitated by cycles of intense
grazing that prevent C. validus from growing out and dominating the canopy. After 17 years,
the sward is increasingly composed of a variety of species with favorable grazing characteristics.
Prior to targeting C. validus with fire and heavy grazing, areas occupied by C. validus dominated
veld were in a poor condition and offered zero contribution to livestock production. Through
burning and intense grazing, management was primarily able to make use of underutilized C.
validus swards. Veld condition improved as the consequent species replacement that followed
now caters for breeding stock, thus increasing livestock production in previously unavailable
Both H. hirta and C. validus are competitive Increaser I species (species increasing in
underutilized veld) that dominate in end point or climax grassland states. That these species are
prone to underutilization (low quality mature sward) means fire is a common and often
necessary tool used to stimulate higher quality forage. However, this study has shown that
annual burning of H. hirta (without grazing) increases seed banks and therefore maintains a
consistent source of seed to maintain its dominance. The value of burning C. validus veld is only
realized when combined with intense and efficient post fire grazing. A sustained cycle of heavy
grazing and rest eliminates this unpalatable climax community and facilitates the development
of a sub climax sward with improved veld condition characteristics favoring livestock
production. In conclusion, both studies emphasize the importance of post fire grazing to
manage and control unpalatable climax swards.