Grass & Ecology

Grass plays an essential role in nature, especially as a source of food, but also to provide shelter and nesting material. There are few food chains that do not include grass in some from or another. The reason for this is that grass occurs very widely over the subcontinent and is virtually always edible. It is usually the animals at the bottom of the food chain that utilise grass. Most predators are therefore indirectly dependent on grass. Let us examine the most important groups of animals that utilise grass:

Grazers

Grazers eat the most grass by far and have the greatest impact on the grass stand. These animals are mainly found in areas with enough grass and may even migrate, or at least have migrated in the past, in search of better grazing. They consume large quantities of grass and form the base of many food chains. They are not only dependent on grass, but grass also depends on them. Grazers remove old plant material, stimulate new growth, and also provide fertilizer in the form of manure. Examples of typical grazers are buffalo, zebra, blue wildebeest and hartebeest; usually animals found in large herds. Today the habitat of many of these animals has been taken over by cattle and sheep.

Rodents

Most rodents, including the larger species such as spring hares and cane rats, eat grass seeds and/ or the base of grass culms. Reserve nutritious matter is stored in the base of the grass culms, making this a very nutritious part of the plant, of which animals are particularly fond.

Birds

Apart from birds such as the sociable weaver and finches which use grass to make their nests, or which hide in reeds, there are many species which only feed on grass seeds. The most common of these is the red billed quelea (Quelea quelea). Quelea finches are the most common birds on earth and there are estimated to be as many as 1,5 billion of the in Africa. They are unfortunately a big problem as they consume thousands of tons of grain, particularly wheat and sorghum, from cultivated pastures annually. Seed-eating birds such as finches and doves mainly eat grasses with round seeds and probably play and important role in the dispersal of these seeds. Such grasses, such as Panicum maximum, Panicum deustum, Setaria megaphylla, Setaria sagittifolia, Brachiaria deflexa and Sporobolus panicoides, often grow in the shade under the trees where birds often congregate. These grasses grow best in nitrogen-rich soil that has been enriched with guano.

Insects

Many insect species use grass for food and shelter. Locusts and termites, in particular, can consume large quantities of grass material in their large numbers. The brown locust (Locustana pardalina) is known to occur in swarms of up to 3 million and can remove tons of grass from the veld in a very short space of time. A similar plague, the Sahara Desert locust, occurs in North Africa. Harvester termites (Macrotermis species) or fungus growers, as they are also known, cut the grass culms, leaves and other organic material up into short pieces and carry them to the bottom of their nests. This material is planted in ‘gardens’ and used to cultivate fungi, which serve as food.

(Guide to Grasses of Southern Africa, Frits van Oudtshoorn)