Blazing or grazing – the great fire debate
Fire is a natural ecological process that has occurred for millennia on the grasslands of Africa. One of South Africa’s leading fire ecologists, Prof Winston Trollope, explains:
“The African continent is prone to lightning fires and has an ideal fire climate with dry and wet periods. African ecosystems evolved in the presence of early man who has been burning for more than a million years; this is why we need to include lightning and humans in our understanding of fire and fire systems.”
His research in the Kruger National Park showed that lightning accounted for 10% of veld fires, while 90% were caused by humans. While fire, humans and herbivores may have evolved together, there are differing schools of thought as to whether the use of fire as a management tool, in the form of prescribed burning, promotes or undermines grassland and veld condition.
Some ecologists, including Prof Trollope, maintain that burning is critical in herbivore management and is necessary for the ecological well-being of grassland and savannah ecosystems. Holistic grazing pioneer Allan Savory counters this approach saying that burning is a key contributor to the decline and desertification of grasslands. Allan says that while fire can play a useful role in land management, it should be cautiously used with an understanding of soil and plant life. He explains that fire is used excessively by too many farmers; an approach that contributes to soil erosion.
“Africa is burning about a billion hectares a year, causing immense carbon emissions that are significantly contributing to climate change and destroying the soil. Soil is a living organism like skin; if you burn too much of it, it dies. Dead soil cannot support healthy vegetation and each time you burn you destroy plants and the litter between them,” says Allan.
“Exposed soil inhibits the establishment of new plants that require cover and moisture. Water absorption is reduced as run-off on exposed soil increases. We need plants to be closely spaced to bind the soil and make the rainfall more effective. “To achieve healthy soil and healthy vegetation in our grasslands certainly requires disturbance, but many people think this means burning, when animal impact achieves the same results without the adverse effects of fire,” he explains.
Allan says that numbers of large herbivores, such as cattle, can graze in contained groups continuously on the move to simulate the grazing patterns of migratory antelope. Prof Trollope agrees there are many merits to holistic planned grazing and that the use of fire should always be carefully considered. “While my approach to fire is different to Allan’s, farmers must be aware that fire is an extreme defoliation treatment and they should be absolutely clear about the reasons for burning. It is definitely kinder to graze than to burn but it is not always practical, particularly when farmers are dealing with tight financial margins,” he says.
For example, using animals to graze down moribund veld takes much longer than burning it down. Allan stresses that the true cost of fire is higher in terms of soil and plant damage and atmospheric pollution. Explaining the atmospheric pollution, Prof Trollope says, “Fire certainly results in a cyclic release of carbon dioxide through the combustion process, but this is re-absorbed in the following growing season via photosynthesis during grass regrowth.
“In the African grasslands and savannahs, fire does not contribute to net elevated levels of carbon dioxide. This is not the same as using fire to convert tropical forest to cultivated pastures.” Prof Trollope acknowledges that misuse of fire can be damaging and costly and emphasises that burning is a specific tool to be used for specific purposes. Routine burning, carried out as a seasonal habit, can lead to long-term, negative changes in grassland composition. Many farmers habitually burn without thoroughly understanding what they are doing.
“Farmers are people of habit and like to do things on a routine basis. The practice among farmers in the sourveld grasslands is to burn every four years to remove moribund and unpalatable grass material and to prevent shrub species encroachment. “When a grassland is burnt too often the cover declines, resulting in accelerated soil erosion. It also leads to a predominance of pioneer/Increaser II grasses, lower canopy cover, diminished species diversity and veld condition.”
Prof Trollope says it is better to have a variable burning frequency in response to variations in rainfall and stocking rate, and to base decisions on the ecological status of the veld. “We must clearly understand the reasons for burning, the condition of the veld and how to manage the veld after burning,” he explains.
Burning to remove moribund material
It is a good idea to burn if the grass is self-shading and is becoming overgrown and unpalatable. Removing moribund vegetation also helps to reduce the tick load. The herbage mass or the dry weight of the combustible material can be assessed using a disc pasture meter calibrated for use in African grasslands. Visual assessments can be used by more experienced veld managers. When the grass reaches or exceeds 4 000kg/ha it is considered moribund and can be burnt. Under these conditions stockmen should reassess their stocking rates as the rangeland is probably under-utilised as a result of understocking.
“It is equally important to understand how different species respond to fire,” says Prof Trollope. He agrees with Allan that growth of woody species, such as the sickle bush (Dichrostachys cinerea), common in bushveld areas throughout South Africa, is often stimulated by fire.
“A plant with one stem before a fire can be stimulated into multi-stem growth post-burn. Only a few woody plants are killed by fire and repeated burning without a sound grazing and browsing system can reduce woodland biodiversity.” Prof Trollope explains that the bossieveld in the Karoo is governed by the same rule and certain species such as bitterbos (Chrysocoma ciliata) start to dominate.
“If we look at the encroachment of fire-resistant woody species in the Bedford/Adelaide area of the Eastern Cape, such as sweet thorn acacia (Acacia karroo) and blinktaaibos (Rhus lucida), we can trace this encroachment directly back to early settler farmers who shot out the large browsing wildlife species (such as elephant, giraffe and rhino),” he says.
“On top of this, the settlers generally did not like goats so this component was absent and the remaining browsers, such as kudu and bushbuck, were not present in sufficient numbers to control the bush.” Since July 2001 Prof Trollope has conducted several controlled burns to deal with bush encroachment on Lochart Ainslie’s farm, Glen Gregor, in the Bedford area.
“Once you have burned you need to keep regrowth under control by using species such as impala and nyala in wildlife areas and domestic livestock in farming areas,” says Prof Trollope. The time of the burn and the intensity of the fire are other critical aspects of fire management – to remove moribund material burn after the first rains when the fire hazard is low. For a hotter fire, to control woody encroachers, burn before the first rains.
“Burn when the grass is dormant (in winter) and burn as close to spring as possible so that the grass regrowth is fairly quick,” says Prof Trollope. “The least damage is done when grass is dormant. When grasses frost off in winter their growing points are at soil level away from the impact of the fire. If growing points are elevated there will be high mortality from fire.”
Prof Trollope emphasises that farmers should be cautious around fire and ensure that there are adequate firebreaks, sufficient well-trained personnel and equipment. “Farmers should familiarise themselves with the National Veld and Forest Fire Act (No 101 of 1998),” he adds.
Allan is generally opposed to farmers using fire as a management tool as he feels the damage to grassland ecosystems is severe, while Prof Trollope believes that the controlled use of fire can be highly beneficial to grassland ecosystems and improve the carrying capacity of the veld. Both approaches have been thoroughly researched over many years and both Allan and Prof Trollope have been widely published.
To gain a better understanding of the complexities of grassland and savannah ecosystems, farmers are encouraged to take the time to understand the dynamics of fire climax regimes. Commonly held theories are constantly assessed and reassessed as advances are made in grassland science.
Temperature and weather conditions are critical
To remove moribund and unpalatable grasses plan a cool fire. The heat intensity of a fire is determined by fuel load, air temperature, relative humidity, grass curing and wind speed. Moribund veld with a grass fuel load of >4 000 kg/ha has sufficient fuel for a fire. Burn when the sward is dormant, after the first rains. Set the fire when the air temperature is less than 20°C and the relative humidity above 40%.
These conditions are good for a cool burn. Wind speed should be a maximum of 15km/ hr but 10km/hr is more ideal. A cool burn will achieve a ‘mosaic’ or ‘patch burn’ effect, irrespective of the size of the land. Patch burning results in a mosaic of burnt and unburnt areas, which reduces the fire hazard and provides biodiversity ‘islands’ for a range of species.
When burning woody thickets and species such as renosterbos (Elytropappus rhinoceratis), a hot fire is required with temperatures of 25°C and above and a relative humidity less than 30%. In hot, dry conditions, like those of a Berg wind, a ‘clean’ burn can be achieved. High temperatures cause combustion to take place more readily and the flammable material does not have to absorb heat energy to be raised to ignition temperatures. A fire of this intensity will kill the upper canopy in trees and shrubs up to a height of 3m and make vegetation available for shorter browsers.
Rangeland fire management practices
Prof Trollope says that for a burn to take place there should be sufficient fuel to support the fire and the veld should be in good condition, reflected by adequate cover and the required species composition. Decreasers are palatable, productive forage grasses while Increaser I species are less palatable and indicate undergrazing or selective grazing. Conversely, Increaser II species are pioneers that are less productive and increase with overgrazing.
Grass species that dominate when grassland is subjected to moderate intensity and frequency grazing. Rooigras (Themeda triandra) is a familiar decreaser.
Grass and herbaceous species that dominate when grassland is subjected to low intensity and frequency grazing. Turpentine grass (Cymbopogon plurinodis) is an Increaser I.
Grass and herbaceous species which dominate when grassland is overgrazed with high intensity and frequency grazing. Steekgras (Aristida congesta) is an Increaser II. In veld dominated by decreasers, burning is ecologically permissible, but only necessary if the grass fuel load is >4 000 kg/ha. In Increaser I dominated veld, burn to adapt to a decreaser status. Conversely, if the veld is dominated by pioneer Increaser II species, it is ecologically sensitive and should not be burnt. In decreaser, Increaser I and Increaser II dominated veld, one can use high density, short duration grazing to rehabilitate or invigorate veld, followed by rest periods – from a few months to one year. It will simply take far longer than burning.
“Conventional wisdom dictates that veld should be rested after a burn to allow the grass to recover. Sweetveld should be rested for a growing season and sourveld should be allowed to recover until it reaches a height of about 10cm,” Prof Trollope explains.
“However, research conducted by Professor Kevin Kirkman of the University of KZN and Dr Peter Zacharias who conducted his research at the Dohne Research Station found that veld can be grazed immediately after a burn once sufficient greenery has emerged. This will ensure optimum animal performance and good grass cover and vigour, if the veld is managed using a sound grazing and resting system,” he adds. “Veld should be rested for a year every three to four years to maintain the vigour and cover of the grass.”
Originally published on farmersweekly.co.za