The perennial grass known as Red Oat Grass, or Themeda triandra, is a foundational species across the African savanna ecosystem. This grass forms dense tussocks, often turning a characteristic reddish-brown color as it matures. Its abundance makes it the most common grass in African natural grasslands. The grass’s palatability, especially when young, establishes it as a major food source, supporting a complex web of herbivores that rely on its abundance for survival.
Primary Consumers: Migratory Herds
The most impactful consumers of Red Oat Grass are the migratory herds of ungulates that move across the savanna in search of forage. The Great Migration relies on the seasonal flush of highly nutritious grasses like Themeda triandra. These large grazers are attracted to the grass when it is young and green because it offers a higher concentration of crude protein. Research indicates that the crude protein content can range from 2.8% when mature to over 12% in its early vegetative stage.
Wildebeest and plains zebra form the bulk of these migratory groups, with each species occupying a slightly different niche in consuming the grass. Zebras, as bulk grazers, generally arrive first, preferring the taller, coarser parts of the grass, which helps them meet their high energy demands. Their less selective grazing prepares the landscape for the wildebeest, which are more selective and prefer the shorter, younger shoots closer to the ground. This sequential grazing pattern ensures a more complete utilization of the Red Oat Grass biomass across the savanna.
Other large migratory antelope, such as the Hartebeest and Topi, also feed heavily on Themeda triandra during their local movements. While mature Red Oat Grass offers a lower nutritive value and higher fiber content, the sheer quantity of the grass allows these animals to maintain their body weight during the dry season.
Secondary Consumers: Resident Grazers and Insects
Smaller, resident herbivores and invertebrates also consume Red Oat Grass. Non-migratory antelopes like Impala and Thomson’s gazelle feed on the grass, often switching between grazing and browsing on shrubs depending on the season and grass maturity. Gazelles frequently consume the new shoots that emerge after the larger herds have passed, which is a form of facilitation in the grazing succession. The Southern African leopard tortoise is a specialist grazer in some regions, relying on Red Oat Grass as a significant part of its diet.
A less visible but widespread consumption comes from the savanna’s insect populations. Grasshoppers feed directly on the leaves and stems, with swarms capable of stripping large areas of vegetation. Termites, such as harvester ants, also collect the grass and seeds to store in their mounds, influencing local nutrient cycling. These smaller consumers ensure that even the biomass that is not eaten by the large migratory herds is processed.
How Grazing Maintains Grassland Health
The consumption of Red Oat Grass by this diverse range of herbivores is essential for the grass itself. Grazing acts as a form of biomass removal, preventing the grass from becoming choked with old, moribund growth. Removing this dead material promotes the emergence of new, healthy shoots, which are more vigorous and nutritious.
The actions of the grazers also assist in the grass’s reproductive cycle. As the animals move, their hooves disturb the soil, which helps to break up the dense grass tussocks and create microsites for seed germination. Furthermore, the characteristic awns on the seeds enable them to attach to the fur of passing animals. This attachment facilitates long-distance seed dispersal, ensuring that the Red Oat Grass can colonize new areas and maintain its dominance across the vast savanna landscape.