A fire break a year later
The photograph on this post was taken of a 2010’s firebreak, which was not repeated in 2011. The new growth on the break is distinctly different from the surrounding (unburnt) grassland as may be expected. However, closer examination shows that the growth on the firebreak is almost entirely Hyparrhenia hirta (thatch grass) with some Cymbopogon excavatus (turpentine grass). What is significant, is that when Egoli Granite Grassland is considered degraded, Hyparrhenia hirta dominates.
GJ Bredenkamp explains that “anthropogenic Hyparrhenia hirta dominated grassland” is what replaces the threatened Egoli Granite Grassland. In other words, the activity of man – in the burning of a fire break – is transforming the grassland.
The study quoted above references “Vegetation in Southern Africa” by RM Cowling, DM Richardson and SM Pierce (2004); V International Conference on Forest Fire Research, 2006
These authors state:
Fire is widely used for management purposes in more humid “sourveld” grasslands to maintain the vigour and palatability of the grass sward. Fires are burnt at annual or biennial frequencies (1-2 year intervals), since fuel accumulates rapidly in these systems. Season of burn is determined by efforts on sward productivity and composition, the condition of plant cover in relation to wind and water erosion and the hazards of runaway fires. In general fires in the dormant season or early in the growing season are most favoured for maintaining grass productivity and composition. Fires in the summer growing season have detrimental effects on grass cover and composition. Many grasslands are also being colonised by invasive alien species (including Australian Acacia species and pines (especially pinus patula). Frequent fires can be used to suppress the invasion process.
The key principle driving the use of fire for controlling bush encroachment involves burning at frequencies and intensities that will prevent juvenile trees from escaping the height where the canopy is no longer killer by fire. Fires burnt at the end of the dry season, after trees have leafed out but before rains have initiative grass growth, are most effective at reducing tree biomass. Fires burnt during or toward the end of the rainy season, favour woody plants at the expense of grass.
Fire and Conservation
Fire prescriptions developed for livestock farming have often been applied to nature reserves to promote the large mammal component. Recently this farming approach to fire has come under criticism, since it might promote some components of the biota at the expense of others.
…in Grass and Savanna biomes, calls have been made for more variable fire-regimes (varied frequencies, varied seasons, varied burn intensities) in conservation areas in line with the objectives of conserving biotic diversity.
Where feasible “natural” fire regimes have been proposed, meaning in practice, the lightning fires be allowed to burn and other fires suppressed. The rationale is that the fire regime under which the biota evolved is most likely to ensure survival.
One problem with this approach is that it has no predictive value. A “Natural” fire-regime may produce undesirable changes in terms of other management objectives, but the cause of these changes requires understanding of fire/plant interactions.
Humans have ignited fire in the region for hundreds of thousands of years at unknown season, frequencies and intensities. The spread of the fires from an ignition site has been curtailed by extensive fragmentation of nearly all fire-prone vegetation by roads, buildings, croplands, etc. Fires ignited by lightening in most contemporary landscapes will not be able to travel as far as they did in the past, this confounding the attempts to recreate “natural” fire-regimes. Nevertheless, for economic reasons along, fire management is likely to become more expensive and fire-regimes less rigid in conservation areas in the future.