Late summer burns

Conventional, or rather dogmatic, conservation practise dictates that management burns should be restricted to the end of winter just prior to the onset of the rainy season.

Although natural lightning strikes are responsible for a lot of natural fires at this time, the exclusion of fire throughout the rest of the year does not necessarily make good conservation sense.

If the purpose of conservation management is to maintain the natural functioning of ecosystems, then one has to take cognisance of the processes that were instrumental in shaping the landscape. Geology and climate are considered to be the key determinants of savanna ecosystems at very broad spatial and temporal scales. At finer scales, however, herbivory and fire are considered to be the key determinants, with fire playing an important role as a disturbance process in maintaining the grass/tree mix that characterises savannas.

Historically, fires in savannas would have been started by lightning strikes at the onset of the rainy season, but there is also a lot of evidence to suggest that anthropogenic fires, or fires started by people, played a critical role in shaping savanna vegetation structure. The numerous and widespread pastoralist communities that inhabited the savannas of Africa set fires to supplement the nutrition of domestic stock during the dry season and hunters set fires to attract game. These fires would have occurred randomly throughout the dry season and would not have been restricted to the short period at the end of winter prior to the onset of the rainy season. The exclusion of these anthropogenic fires has therefore been questioned and as a result, conservation managers are increasingly applying fires throughout the year in an effort to simulate the historical influence of anthropogenic fires.

The Waterberg represents a moist infertile savanna dominated by broadleaf deciduous trees and tall, unpalatable perennial grasses. The accumulation of fuel in moist savannas suggests a fire return interval of between one to three years. However, it is reasonable to assume that large tracts of the Waterberg burnt annually prior to anthropogenic landscape fragmentation. This can be assumed from the high levels of primary production and thus fuel accumulation combined with low levels of grass consumption by herbivores and high incidence of lightning strikes. Given the low grazing value of the Waterberg during the dry season, it is reasonable to expect that the area was not directly subject to anthropogenic fires but may well have burnt as a result of anthropogenic fires moving into the mountains from the surrounding plains.

Previously, Welgevonden management adopted a laissez-faire approach to fire management in that naturally occurring lightning fires were permitted to burn provided they did not threaten infrastructure or threaten to escape onto neighbouring properties. However, the presence of numerous artificial barriers in the landscape (such as roads, firebreaks, fencelines etc) greatly restricts the spread of natural lightning fires across the landscape and the laissez-faire approach is not sufficient to replicate the historical influence of fire. Consequently, management has taken the decision to implement a more pro-active burning regime which entails burning up to 10% of the reserve each year at the end of summer. This is to replicate the presumed influence of anthropogenic fires and we expect that the green flush resulting from these late summer fires will provide valuable grazing into the long dry season and as such will improve the fecundity of the large herbivore populations.

This year, a large block of around 3500 hectares in the central-north section of the reserve has been burnt and the late rains received at the beginning of May have contributed to the rapid emergence of a vigorous green flush that is being greatly appreciated by the grazing herbivore populations.

August 2009

Approximately 3600 hectares were burnt using lodges in the block as point ignition sites so as to create a secure firebreak around the lodges. The purpose of the late summer burning programme is to mimic the historical influence of pastoralists on the landscape and to re-establish fire as an important disturbance process in maintaining ecosystem function.

Shortly after the burn, the reserve received several days of good rainfall and this has contributed to the emergence of a vigorous post-burn green flush which is being greatly appreciated by the populations of grazing herbivores. We anticipate that the green flush will provide good grazing for an extended period into the dry season and in doing so we hope that it will promote herbivore recruitment through the provision of nutritious grazing during the mating season.