Verloren Valei is typified by its grasslands, and understanding them is essential to managing the reserve and preserving its huge biodiversity.
By Mike Zingel
When they think of Verloren Valei, people associate the place with orchids, birds or wetlands generally. But in reality it’s the grasses that are this unique reserve’s most defining feature. Grasses are the dominant vegetation, covering the entire reserve, including the Ramsar wetlands, which are unique in that they are not open freestanding water as is the case, for example, at nearby Lakenvlei.
The geology and consequently soils on the reserve are important determinants of the grass cover. Verloren Valei is characterised by hard silicate ridges separated by more erodible dolerite intrusions that were laid down many millions years before the evolution of grasses. Erosion over the years has removed around one kilometre of depth of the original formations.
The soils on the ridges are shallow and sandy due to the silicate parent material, while on the midslopes and valley bottoms the soils are deeper, have a higher clay content and are more fertile thanks to the dolerite parent material. The midslopes are the areas with most grass and are consequently much frequented by game.
Grasses appeared just prior to the fifth extinction event 66 million years ago, and survived into the subsequent Cenozoic Era in which we currently live. Grasses have evolved over the same time period as the equally successful orchids, which are also a feature of Verloren Valei. The grass family Poaceae and orchid family Orchidaceae are within the top five plant families in the world today in terms of numbers of species.
The evolutionary paths of both grasses and orchids have followed parallel courses, with both developing strong symbiotic relationships with soil microflora, particularly mycorrhiza fungi. Among orchids these are frequently species-specific, while with grasses this is less so. Seeds of some orchid species will not germinate unless their specific mycorrhiza is present. Similarly, these mycorrhiza die out if their particular orchids are not present.
Grasslands are effective carbon sinks
The fact that grasses have a less specific relationship with mycorrhiza fungi is an evolutionary adaptation that makes it easier for new grass species to enter existing grass communities.
This symbiosis between grasses and soil microflora, including mycorrhiza, is vital to building up soil organic material of which carbon is a basic component. Grasslands are now considered to be prime carbon sinks on earth, surpassing forests in sequestrated carbon per hectare.[1] Topsoil in healthy grassland can sequester up to 4% carbon as compared with a national average of under 1% for South Africa as a whole. The lower national figure is due to crop farming and inappropriate veld and pasture management.
At present carbon content of the midslopes soil of Verloren Valei would probably be at the higher level. A rough calculation estimates that the carbon in these soils would be equivalent to carbon in aviation fuel sufficient for over 5,000 return flights from South Africa to Europe by Boeing 747. Verloren Valei’s ecological value in terms of sequestrated carbon is clearly very high.
Anatomy of Verloren Valei’s grasslands
Verloren Valei can be broadly divided into three vegetation units, each characterised by a distinctive plant species:
- Tristachya leucothrix (Hairy Trident Grass) Grassland, covering 70% of the reserve, chiefly on the midslopes
- Coleochloa setifera (a species of sedge) covering 20%, mainly on the crests, but extending into rocky parts of the midslopes
- The wetlands, some of which are Phragmites australis (Common Reed) Wetland and the rest Andropogon appendiculatus (Vlei Bluestem Grass) Wetland.
The positions of vegetation units are determined by the nature of the environment (or biome), and consequently do not vary over the short term. However, plant population dynamics are constantly at work within the units, with the species present, and their relatively proportions, constantly changing. The grass component is the quickest to respond to external impacts, including grazing and burning, making it a good barometer of the health of the overall vegetation unit.
In places were the climate is characterised by harsh, long, dry winters and summer rainfall, we typically see competition between grasslands and savannas. There is dynamic competition between grasses and trees.
Verloren Valei, and the Dullstroom area, is typically grassland. Grasses grow prolifically in summer, providing abundant fuel for fires started by lightning strikes. Because grasses recover from fire much more quickly than trees, the predominance of grasslands becomes stronger.
Managing grasslands
Managing grasslands is clearly vital, particularly at Verloren Valei, but it is very difficult owing to a number of factors.
The first point to notice is that grasslands evolved over hundreds of thousand years to cope with being grazed by herds of tightly packed grass-eating animals that migrated seasonally over vast distances. Close packing in the herds was due to pressure from large carnivores. The consequence was heavy grazing, copious dung deposits and urination plus hoof action on the soil. Because the animals were so densely packed, selective grazing was not possible, and palatable and unpalatable grasses alike were grazed. Dung and urine returned nutrients to the soil and some additional organic material. Hoof action promoted regeneration of the veld due to seeds being incorporated into the top layer of the soil. Because the land was effectively “empty”, the herds had vast areas in which to roam, giving the heavily grazed grasslands time to recover.
Traditional pastoralists in Africa and elsewhere mimicked these patterns of exhausting the grazing in one place before moving onto the next.
However, once the land was cut up into farms and confined reserves and at the same time large carnivores were substantially reduced, the delicate balance between animals and grasses was fundamentally destroyed. As a consequence, veld in Southern Africa and similar regions of the world (like the North American prairies where huge herds of Bison ranged) have degenerated.
Because the migratory patterns of the game and pastoralists’ herds are no longer possible, the grasslands become simultaneously understocked and overgrazed: understocked because the smaller areas of individual farms can only sustain small populations of animals on a permanent basis as compared to the much larger populations of the migrating herds; and overgrazed because the lower concentrations of animals have the time and space to graze selectively. In turn, this means that the palatable grasses are never given enough time to recover and so the unpalatable ones spread.
The consequential reduction in grass cover and drop in soil microflora causes large amounts of carbon to be released into the atmosphere.
Some possible solutions
In the Dullstroom area, including Verloren Valei, the farmers used to practice a form of transhumance, a seasonal movement of livestock from winter pastures in the Lowveld to summer pastures on the high-lying ground. This meant that the veld in each area was flattened but then had time to recover. Nowadays, farmers and the reserve management at Verloren Valei mimic this pattern to some extent by periodic block burning in spring.
The spring block-burning is complemented by mosaic burning at the end of summer. At this time, patches of unpalatable grass that have not been grazed and are now dry and inflammable are burned while surrounding grazed veld that is still green will not burn. This process reduces the less desirable species.
However, these efforts by farmers and reserve managers are by no means a complete solution, and the overall condition of grasslands managed in this way is likely to deteriorate steadily. The more palatable grasses will be persistently overgrazed with not enough time to regenerate, allowing the less palatable species to proliferate. One potential approach is being pioneered at the Herding Academy in Graaf Reinet, where shepherds are learning to mimic the migratory habits of game and almost-forgotten traditional knowledge. Perhaps this kind of thinking could be applied more widely in other biomes.
Turning the clock back 100 000 years obviously can’t be done, but the rising generation will have to develop sustainable solutions if the vast rangelands of the world, nature reserves and farms alike are to be restored and fulfil their roles both as carbon sinks and habitats for animals.
[1] See, for example, UC Davis, “Grasslands more reliable carbon sink than trees”, Phys.org (9 July 2018), available at https://phys.org/news/2018-07-grasslands-reliable-carbon-trees.html.
