Enviro Perspectives on Succession with Dave Rushworth
SuccessionThe concept of succession is normally related to physical aspects but it can be used to describe the inter-related processes in animal behaviour and activities. In the inter-relationships of life, we will all be aware of 'actions and reactions' - 'cause and effect', etc.
Everything has some effect on something else around it and nothing can exist in complete isolation to its surroundings. There are many examples of natural sequences that take place as a result of some initial activity and it is worth highlighting some of these events. Rather like the 'chicken and the egg', one could argue where it all begins. Ignoring the effects of geology, soils and climate, focus will be on the succession of animal activities with particular emphasis on some species which appear to start a sequence of activities. These animals we will call 'trigger species'. They 'cause' things to happen while other species follow on with the 'effects'.
These trigger species are often the most important to conserve in the management of other species that rely on their activities. There are many minor, but not less important, species not mentioned here. Spiders that provide building material; wood pecking birds, various types of weaver birds and hammerkops, whose nests are used by others; hippo, fish, reptiles and many others, all deserve consideration.
TermitesThere are numerous species of termite active in a great variety of habitats. Some are mound builders while others are subterranean or surface foragers. Without going into the complicated life histories of termites, most of them can be considered trigger species in their recycling of nutrients and in their recovery of minerals from deep in the soil. As a direct source of food for other species or because of their mineral-rich mounds, they create conditions for the survival of other animals and plants.
The clay mounds are islands of food and moisture that are very attractive to animals and seed growth. Good tree growth provides attractive habitat for more animals which deposit more nutrients - and thus an island of high activity is created - all started by the termites.
Old termite mounds are used by a variety of reptiles and small mammals, such as mongooses, and the dispersing nutrients enrich the surrounding grasses for large ungulates. With exception of those destroying valuable property - all termites deserve protection.
Aardvarks (Antbears)These termite-eating mammals are normally nocturnal and rarely seen but are extremely important in our savannah systems. Attracted to deeper soils, their foraging diggings may only serve to catch run-off water while their deep, residential burrows are a real 'starter pack'. When aardvarks move to new feeding areas, their holes are taken over by a variety of other animals that unable to dig or have difficulty in constructing their own burrows.
Warthogs are well known followers that would find it hard to reside in an area without the refuge of antbear holes, down which they sleep and breed. The same applies to hyenas and a host of other mammals that rely on these burrows.
Where there are no sand banks, the walls of unoccupied burrows are excavated by certain birds for nesting holes. The rare blue swallow is recorded constructing nests on the walls of antbear burrows in the highveld. Many reptiles and insects use the burrows in a sequence of occupation that make aardvarks a true trigger species.
Buffalo (Elephant And Rhino)These large mammals are obvious trigger species. Apart from the pan-constructing activities of mud-wallowing, these large mammals 'survey' and open up 'main roads' through thick bush and over long distances. Black rhino access dense thickets. Elephant lower the browse for other species and provide ground cover for small mammals and ground birds. They open up water holes in dry river beds and trigger many habitat changes beneficial to other animals.
In areas of grass too thick and coarse for access by smaller mammals, buffalo are nature's mowing machine. In the dry months preceding the rains, buffalo herds gather in large aggregations of up to several thousand animals. Apart from this activity simulating a cattle sale - where breeding animals may change herds - a more important land-management activity takes place.No grazing area is sufficient for such numbers for any length of time, so the aggregation has to keep moving. Even when not grazing, their feet are churning up the soil surface and their numerous droppings are fertilising the area. They trample open unpalatable grass growth and flatten the vegetation for protection of the loosened soil.
Like a huge mowing machine they keep on the move through the thickest grass areas until the onset of the rains, when they break up again into their smaller herds. Other large ungulates also aggregate during the dry season - possibly for breeding purposes - but probably don't have the same effect on the veld as the heavy buffalo.In the wake of the buffalo, new growth attracts more delicate grazers - tsessebe, hartebeest and others. As grass growth progresses, sable, roan and others will feed among the long stems shunned by wildebeest, zebra and impala, until it becomes too dry and coarse - when the cycle starts all over again. This grazing sequence - or 'succession' - is much more beneficial to grasslands than burning.
Organic composition is maintained with good cover and nutrients intact. Moribund (tall, dead) grass will shade itself out if not opened up to the light - but fire is a very second-best management tool, destroying nutrients, decomposers and ground cover. Large buffalo aggregations are an excellent example of a trigger-species in grazing succession.
ConsiderationsExcept in very large, wild areas, it is almost impossible to retain the dynamic, natural aggregations. Fences imprison and constrict wild species from their natural functions. Like human prisoners, they are 'jobless' and restricted to an existence of mere survival for the benefit of ownership and greed. Rearguard management activities can not match nature's diverse systems.
Until humanity learns to share and conserve, gradual destruction of resources will continue. One thing we can try and preserve in our restricted spaces are those trigger species that stimulate the continuation of natural processes. There are many. Think about them and do something to ensure their survival until humanity regains true consciousness.