Effect of fire frequency on herbivore distribution and behaviour in the Kruger National Park, South Africa.
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Date
2012
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Abstract
Fire plays an important role in structuring and maintaining savanna grassland ecosystems.
Although regular fires are a characteristic feature of savannas, the effects of fire frequency on
these systems are less well known, particularly with respect to how frequency of fire influences
large herbivore distribution and behaviour. The expectation is that large herbivores should be
attracted to frequently burned sites as a consequence of changes in forage quality and quantity,
and/or vegetation structure and composition. The former could be driven by alterations in soil
nutrients, such as N and P. Alterations in vegetation also could be important in determining risk
of predation. For example, an increase in woody vegetation could decrease predator visibility
making large herbivores more vulnerable to predation. The objectives of this study were to
investigate the effects of long-term alterations in fire frequency on herbivore distribution and
behaviour, as well as the mechanisms (soil nutrients, vegetation structure and composition, and
forage quality and quantity) potentially driving the distribution of large herbivores. To address
these objectives, I conducted large herbivore surveys on a bi-weekly basis from 2009-2010 in a
series of plots in the Experimental Burn Plots (EBPs) burnt at different frequencies (annual,
triennial and unburnt) over the last five decades at three study sites in the Kruger National Park,
South Africa. Surveys also were conducted on new plots that were established adjacent to the
long-term plots. These new plots have a fire return interval of 4 years which is similar to the
triennially burned plots of the EBPs. They were established in the landscape adjacent to the
EBPs to assess whether the responses of herbivores to fire observed in the EBPs reflected was at
landscape level.
The distribution of all large herbivore species combined and of grazers (e.g. zebra) or browsers (e.g. kudu) only were not affected by fire frequency. In contrast, the abundance of mixed-feeders, such as impala, was significantly higher in the unburnt (control) and annually
burned plots than the triennially burned plots. Although season did not have a significant impact
on the distribution of browsers and mixed-feeders, overall more grazers were recorded across all
burn treatments in the dry season compared to the wet season. Similar patterns of herbivore
distribution were observed between the new plots and the triennially burned EBP plots,
suggesting that responses observed to the long-term fire frequency treatments reflects herbivore
responses at the landscape level. The long-term fire frequency treatments significantly affected
soil nutrients (N, organic C, P, and K were significantly lower with annual burning), vegetation
structure (abundance of woody plants were greater in unburned plots), and forage quantity
(unburned plots had higher biomass) but not quality. More frequent fires improved visibility by
reducing tree height and density and herbaceous biomass, thereby potentially reducing predation
risk, when compared to less frequent burning. As a result, herbivores selected sites with more
frequent fires. The behaviour of the herbivore species investigated was predominantly influenced
by seasonal-induced changes to their environment rather than fire frequency. In the wet season
irrespective of the burning treatment visibility was low due to high rainfall that increases plant
biomass, whereas in the dry season visibility was improved because there is little to no rainfall.
This potential alteration in predation risk likely resulted in herbivores being more vigilant in the
wet season than the dry season. Overall, results from this study suggest that the combination of
fire frequency and season drive herbivore distribution and behaviour by altering mainly the
vegetation structure which can influence predation risk.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
Keywords
Rangelands--Fire management--Mpumalanga--Kruger National Park., Herbivores--Behaviour--Mpumalanga--Kruger National Park., Herbivores--Geographical distribution., Herbivores--Seasonal distribution--Mpumalanga--Kruger National Park., Plant communities--Mpumalanga--Kruger National Park., Theses--Grassland science.