Gondwana comprises of Fynbos and Rensoterveld areas. Both Fynbos and Rensosterveld are critically endangered biomes with, renosterveld being close to extinction. These biomes have a fascinating relationship with fire and their plant richness relies heavily on this element. In this post I will focus predominantly on Fynbos as the factors that affect Renosterveld are similar and affect Renosterveld in the same way.
There is an intricate relationship between fire and Fynbos and the cycles between burns determine the health and the sustainability of this extremely precious biome. On Gondwana Game Reserve, every time our Reserve Manager, Joe plans to burn a block my heart leaps with excitement as for months to come there will be a new landscape to explore with new plants germinating weekly – sometimes daily!
Fynbos can be described as fire-loving or pyrophylic as it is dominated by plants that have adapted to fire.
Naturally fire can occur in intervals of 10 to 30 years. Some fynbos plants survive fire by re-sprouting however many are in fact killed and survive in the form of seeds. Fynbos plants have a highly evolved way of producing fire-resistant seeds. Seeds can survive in the canopy of plants, such as non-sprouting proteaceae. Other species have fascinating ways of storing their seeds in seed stores underground. Germination of the seed is stimulated directly by heat or smoke, and indirectly by altered environmental conditions. Other plant species also called re-sprouters can germinate from woody underground root stock that is stimulated to sprout by fire.
Fire acts as a wonderful mineralizing agent for our nutrient poor soils. The ash left by fire returns valuable minerals that were previously held above ground by the plants, back to the soil. Although a burnt landscape looks barren and “dead”, it ensures that water, nutrients, and light are more available after a burn which is important to rejuvenate soil otherwise considered to be nutrient poor. We could assume that the fire stimulated germination that Fynbos is renowned for could be an evolutionary reaction to an increase in the availability of nutrients and resources and the lack of competition after fire. Fire certainly enhances the bio-diversity of fynbos. Many bulbs and shrubs cannot compete with masses of overgrown Fynbos and may remain dormant for years until a fire clears the landscape and makes space for them to grow.
The relationship between fire and fynbos is a delicate cycle. There are factors such as fire frequency, location, season, and intensity will determine the positive or negative affect that fire may have on Fynbos.
Fire that occurs too frequently can destroy seedbanks and plants before they have a chance to drop their seeds. It can take up to seven years after a fire for some plants to mature enough to produce seed. Frequent fires can reduce biodiversity, cause erosion and death or migration of important pollinators and predators. In general fires should occur between 10-15 years to ensure specie richness, however it is better to determine this by examining the veld. When 50% of the population of the slowest growing species within a given area has flowered for at least 3 consecutive seasons, then this is a good time to burn.
Location plays a factor in determining when fynbos should be burnt, and this is largely dictated by aspect and the climatic and rainfall cycles of a given area. Fynbos that is situated in moist mountain and lowland areas should burn every 12 to 20 years. Fynbos in arid areas should only burn approximately every 25 years. These conditions determine the rate of growth and this directly affects when the Fynbos should be burnt.
Fynbos burnt in different seasons is affected differently. The season generally determine the intensity of the fire. Naturally most fires occur in summer. Fynbos plants seem to produce the most seedlings after late summer and early autumn fires. However extremely hot summer fires can destroy seed stores whereas cooler fires can promote germination. Seasonal fires affect the diverse species of fynbos differently. Bulbs survive fire is burnt in the right season. Burning them in winter or spring when they are pushing out their leaves or flowering can cause irreversible damage.
The presence of alien vegetation can also increase the intensity of a fire. Alien vegetation can hold highly flammable oils. This together with the concentration of it’s biomass can create more intense fires.
There is no doubt that fire is critical in the sustainability and the promotion of biodiversity in Fynbos (and Renosterveld). However, the intervals between fire need to be managed carefully and monitored as although fynbos has adapted to surviving fires, there are many species that will become extinct should fires occur too frequently.
Text: Raquel de Castro Maia