Fire is an important and crucial driver within savanna ecosystems and is necessary in maintaining ecosystem functioning. However to use fire as a management tool clear objectives have to be agreed on and the consequences must be clearly understood and effects thereafter need to be monitored and learnt from.
Globally and in South Africa, climate change has had very tangible effects on our ecosystem. Changes in rainfall patterns, increases in air temperature with knock on effects on a decrease in relative humidity continue to steadily increase fire risk of our landscapes.
Over the past decade it has been noted that extreme fire weather patterns has generally increased and fire frequency, size and intensity to levels that we would not have previously experienced historically. A firestorm is a fire which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires forest fires, and wildfires.
The Black Saturday bushfires (Australia February 2007), the Great Peshtigo Fire (USA October 1871) and the Ash Wednesday (Australia February 1983) fires are examples of extreme firestorms. Such fires are usually beyond human intervention and subside only upon the consumption of all combustible material within its locality or when environmental conditions no longer support the continued spread of the fire.
Unfortunately, in the aftermath associated with these extreme fire events are losses of lives (human and animal), habitat, infrastructure and property of unprecedented levels, which translates into economic losses that amounts to the thousand if not millions of Rand.
If the weather parameters are changing, fuels are increasing and sources of ignitions are not limiting thus favouring more firestorm events. The question now begs as to how were predict, prepare, utilise and manage for these events during our fire seasons.
Research undertaken by Professor William Bond, Catherine Browne and Jeremy Midgley from the University of Cape Town has recently demonstrated that these firestorm events should not only be seen for their negative effects on the ecosystem but can possibly be used to tackle the increasing problem of densification of indigenous woody vegetation into our grassland systems. Woody plant cover is currently being favoured as never before in whole history of savannas.
This is mainly due to the fact that the current CO2 (carbon dioxide) level is higher than at least the last one million years and higher CO2 makes woody plants grow faster, sprout better after fire and build defences (spines, tannins) more easily.
Due to this competitive advantage of woody vegetation over savanna grasses, which have evolved under lower CO2 conditions, the encroachment of woody vegetation into our grasslands has increased significantly over the past few decades. This translates into a potential loss of a crucial biome, the savannas, which makes up approximately 11percent of the global and 46 percent of Southern Africa's land cover and provides essential goods and services for millions of people which sustain their livelihoods.
Further work undertaken by Prof Bond and his team in Hluhluwe-Imfolozi Park in Kwa-Zulu Natal, investigating the potential tools that are available to managers to stop forests from wiping out high rainfall savannas under high CO2, include that of herbivory by elephants and other megafauna.
However, elephants and other browsers seem to avoid thickets and do not have an impact. The use of fire under current policies has not worked in Hluhluwe despite high fire frequencies but these fires are burnt too early, under too mild fire weather conditions and are therefore of too low intensities to move into the forest/grassland boundaries.
A recent fire event in Hluhluwe has shed some new light and information in tackling the woody densification phenomena in the park. In September 2008 the newly formed thickets and a forest section in the park burnt down.
Usually fires do not penetrate the forest and thickets stands but the weather conditions (air temperature greater than 30 degrees, relative humidity less than 30% percent and wind speed greater than 30km/hour) under which this particular fire burnt was such that the fire would be deemed a firestorm and was able to move through the stand of thickets and forests and cause severe top-kill or kill many of the encroaching woody tree species.
Analysis of the climatic data from Hluhluwe from 2001 to 2008 demonstrated that the alignment of the 303 weather conditions is very rare, with only 70 hours or 2.9 days allowed for firestorm conditions. Preliminary data from the project in Hluhluwe suggest that burning the veld under weather conditions conducive to firestorms, provides an opportunity to managers to reclaim invaded grasslands by re-introducing frequent late season grass fires.
There are however many safety issues, such as good fire training, equipment and man-power that need to be taken into account before these fires can be effectively and safely be used. Finally the world that we live and manage within is certainly not the same as it used to be and therefore management tools, policies and actions will have to adapt as never before. These situations also serve as a good reminder that when we're out enjoying nature, we do need to be particularly careful about fire - not only causing it, but possibly being caught up in it. photos: Prof William Bond and SAVFIRE
By Navashni Govender