To maintain their vigour and reproductive power all grasses are dependent on being defoliated either by grazing and/or by the use of fire. Which is preferable – grazing or blazing or a combination of both?
Fire is a natural ecological factor that has been occurring since time immemorial in savannas and grasslands on the continent of Africa, as South Africa’s leading fire ecologist Dr Winston Trollope explains:
“The African continent is highly prone to lightning fires and it has an ideal fire climate with dry and wet periods. The ecosystems in Africa also evolved in the presence of early man who has been burning for over 1-million years; hence we need to include both lightning and people in our understanding of fire and fire systems,” says Winston whose research in Kruger National Park shows that lightning accounts for only 10% of burns, the other 90% is by people.
But while fire, humans and herbivores might have evolved together, there are two widely differing schools of thought as to whether the use of fire by humans today – in the form of prescribed burning – promotes or undermines grassland and veld condition.
The first school maintains that the use of burning is critical in herbivore management and is necessary for ecological wellbeing of grassland and savanna ecosystems (Dr Winston Trollope).
The second school maintains that burning is one of the key contributors to the decline and desertification of grasslands (holistic pioneer Allan Savory).
Allan says that while burning sometimes has a useful role to play in land management, it should only be used with the greatest circumspection and understanding of soil and plant life. He asserts that fire is used excessively by far too many farmers and that this approach is contributing to the situation where farmers are producing more eroding land than food at present.
“Africa is burning approximately 1-billion hectares a year and causing immense carbon emissions that are significantly contributing to climate change and destroying the soil. Soil is a living organism like skin, where, if you burn too much of it, it dies,” Allan says. “Dead soil cannot support healthy vegetation and each time you burn you destroy the plants and the litter between the plants. Exposed soil inhibits the establishment of new plants that require litter and moisture, and ultimately the space between plants gets greater and greater, and water effectiveness is reduced as it runs off exposed soil. This is the opposite of what we want to achieve because we need the plants to be closely spaced to bind the soil and make the rainfall more effective.
“To achieve healthy soil and therefore healthy vegetation in our grasslands certainly requires disturbance, but many people think this means using fire when animal impact can be used to achieve the same end but without the adverse effects of fire,” he explains. “By animal impact I mean large numbers of large herbivores, particularly cattle, on the land, tightly herded together, grazing, trampling, dunging and urinating on a piece of veld and then moving on after a brief period, just as the great wildlife herds once did,” he explains.
Winston agrees there are many merits to holistic planned grazing and that the use of fire should be carefully considered. “While my approach to fire is different to Allan’s, I am absolutely clear about the fact that fire is an extreme defoliation treatment and that one must be absolutely clear about the reasons for burning. It is definitely much kinder to graze than burn but it is not always practical, particularly for farmers who are dealing with tight financial margins,” he says, explaining that the system of using animals to graze down moribund grasses, for example, takes far longer than burning.
Allan disagrees that fire is ‘cheaper and quicker’ but adds that the true cost is often higher in terms of soil and plant damage and atmospheric pollution. Winston has a different opinion on atmospheric pollution: “Fire certainly results in a cyclic release of carbon dioxide through the combustion process, but this is reabsorbed again the following growing season via photosynthesis during the regrowth of the vegetation (grass),” he says. “Therefore in the case of African grasslands and savannas burning does not result in a nett contribution to elevated levels of carbon dioxide as happens with using fire to convert tropical forest to cultivated pastures.”
Winston nevertheless acknowledges that misuse of fire can be extremely damaging and costly, which is why he emphasises that burning is a specific tool that must only be used for specific purposes and not simply carried out as a habit. Too many farmers habitually burn without thoroughly understanding what they are doing.
“Humans are creatures of habit and we like to do things on a regular basis – hence the perceived necessity in the sourveld areas amongst farmers to burn approximately every four years to remove moribund and unpalatable grass material and/or to prevent the encroachment of shrub species like renosterbos (Elytropappus rhinoceratis) and harpuis (Europs species),” says Winston.
“I need to emphasise that the damage done by burning too often is that grass cover declines, resulting in accelerated soil erosion. This also leads to a predominance of pioneer/Increaser II grass species (these obviously differ from areas to area), a decline in canopy cover, species diversity and veld condition.”
Winston says it is far better to have a variable burning frequency in response to variations in rainfall and stocking rate of livestock and to base your decision on whether or not to burn on the ecological status of the veld. “In other words we need to clearly understand the reasons for burning, the condition of the veld that is being considered for burning and how to manage the veld after burning,” he explains:
Reasons for burning:
1) Removing moribund material/grasses
If the grass is suffering from self-shading and is becoming overgrown and unpalatable (moribund) and has bare areas developing between the tufts it is appropriate to burn. Removing moribund vegetation can also reduce the incidence of ticks. Determining whether your grass is moribund is fairly simple: it can either be assessed with the eye or with the use of a disc pasture meter, which is available in South Africa and produced by Brian Clarke the former chief technician in the Science Workshop at the University of Fort Hare. Whenever the grass cover reaches or exceeds four tons per hectare, it is moribund and can be considered for burning. Under these conditions it is also advisable to reassess your stocking rate and grazing system because you might well be understocked.
2) Control of encroaching undesirable plants, bushes and trees (indigenous or alien).
“It is equally important to understand how different species respond to fire,” says Winston who agrees with Allan that the growth of woody species, such as the sickle bush (Dichrostachys cinerea), which is common in bushveld areas throughout South Africa, is often stimulated by fire.
Where one stem existed before the fire, afterwards this can lead to several more emerging. He says that only a few woody plants are killed by fire and that fire, particularly the repeated use of fire without a sound grazing and browsing system, can reduce woodland biodiversity. The same applies to bossieveld in the Karoo where certain species such as bitterkaroo/bitterbos (Chrysocoma cilliata) can 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 the early settler farmers who shot out the large browsing wildlife species (such as elephant, giraffe and rhino),” he explains. “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 in sufficient numbers to control the bush.”
Since July 2001 Winston has conducted several controlled burns to deal with severe bush encroachment on the farm Glen Gregor belonging to Lochart Ainslie in the Bedford area. He is extremely satisfied with the results.
“Once you have burned you need to keep regrowth under control by using species like impala and nyala in wildlife areas and domestic livestock in farming areas,” says Winston.
This brings us to another critical aspect if you are going the burning route: which season to burn and the intensity of the fire.
“Burn when the grass is dormant (in winter) and burn as close to spring as possible so that the grass will grow soon,” says Winston. “The least damage is done to the grass when it is dormant because when grasses frost off in winter their growing points are at soil level and away from the impact of the fire, whereas if they are green then the growing points are elevated and there will be high mortality from fire.”
Winston emphasises that farmers should never forget that fires are dangerous and that they need to ensure that there are adequate firebreaks, sufficient well-trained personnel and equipment. “Farmers should also be familiar with the National Veld and Forest Fire Act (No 101, 1998),” he adds.
In synopsis, Allan is generally opposed to farmers using fire because the damage to grassland ecosystems is severe, while Winston 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 Winston have been widely published. Farmers are encouraged to take the time to better understand fire because commonly held theories are being assessed and reassessed all the time towards a better understanding of our complex grassland and savanna ecosystems on this, the continent of fire.
Winston says that if you are going to burn you should burn according to the ecological status of the veld as reflected by the proportion of Increaser and Decreaser grass species in the veld, as he explains:
In general Decreaser grass species are both palatable and productive forage species while Increaser I & II grass species are less palatable and productive.
Grass and herbaceous species that dominate when grassland is subjected to moderate intensities and frequencies of grazing when rangeland/veld is neither under- or overgrazed i.e. it is correctly grazed. A common decreaser species is rooigras (Themeda triandra).
INCREASER I SPECIES
Grass and herbaceous species which dominate when grassland is subjected to low intensities and frequencies of grazing i.e. when rangeland/veld is under- or selectively grazed eg turpentine grass (Cymbopogon plurinodis).
INCREASER II SPECIES
Grass and herbaceous species which dominate when grassland is subjected to high intensities and frequencies of grazing i.e. when rangeland is overgrazed eg steekgras (Aristida congesta).
If the veld is dominated by Decreaser species, from an ecological point of view burning is permissible as the veld is in a good condition, but burning is only necessary if it is in a moribund condition i.e. grass fuel load is >4000 kg/ha.
If it is Increaser I dominant, you can consider burning in order to adapt to a Decreaser status. Conversely if the veld is dominated by pioneer Increaser II species it is an ecologically sensitive condition and should not be burnt.
Alternatively, in Decreaser, Increaser I and II dominated veld one can use high density, short duration grazing to rehabilitate or invigorate the veld, followed by adequate rest periods – from a few months to one year. It will simply take far longer than burning.
In order to remove moribund and unpalatable grass (including suurpol (Merxmuellera disticha), a cool fire should be used. The intensity (heat) of a fire is determined by fuel load, air temperature, relative humidity, grass curing (greenness or dryness of the grass) and wind speed. If the veld is in a moribund condition (>4000 kg/ha), the fuel load is adequate to carry a fire. Grass should be burnt when in a dormant state i.e. during the winter period. Fire should be set when the air temperature is less than 20-degrees Celsius and the relative humidity is above 40%, this will result in a cool burn. It should generally be a cool day and the wind speed should be a maximum 15kms per hour but preferably 10kms an hour.
A cool burn will achieve a ‘mosaic’ or ‘patch burn’ effect, irrespective of the size of the piece of land. Patch/mosaic burning originates in northern Australia where Aborigines would ignite a fire and let it burn, resulting in a mosaic of burnt and unburnt areas, which reduces the fire hazard of a continuous fuel load and provides biodiversity ‘islands’ for a range of species.
When burning woody thickets and thicket species such as renosterbos (Elytropappus rhinoceratis) and harpuis (Europs species), a high intensity (hot) fire is required – temperatures of 25-degrees and above and a relative humidity less than 30%. Generally it should be a hot day, almost approaching Berg wind conditions as this will achieve a clean burn. Berg wind conditions have high air temperature and low humidity, the high temperature causes combustion to take place more readily and the fuel does not have to absorb heat energy to raise the fuel to its ignition point. Relative humidity determines the moisture content of the fuel.
“Conventional wisdom states that one should rest the veld after a burn to allow the grass to recover and that in the sweetveld it should be rested for a whole growing season and that in the sourveld it should be allowed to recover until it reaches a height of approximately 10cm,” Winston explains.
“However, research conducted by Professor Kevin Kirkman from the University of KZN and Dr Peter Zacharias who conducted his research at the Dohne Research Station found that veld can be grazed immediately i.e. as soon as possible after a burn once sufficient greenery has emerged, which will ensure optimum animal performance, good grass cover and vigour, provided the veld is managed using a sound grazing and resting system,” he adds. “Kevin and Peter recommend that burnt veld is rested every three to four years for a whole year to maintain the vigour and cover of the grass.”