September 2022

The dead trees of the Kruger National Park


The dead trees of the Kruger National Park

The one thing you notice when you are on safari is the vast number of dead trees scattered across the landscape, like perfectly placed ornaments adding depth to any scene they stand in. Unlike ornaments that just serve to be visually pleasing, dead trees serve various purposes in the bush, but before we go into the ‘how’ we need to discuss the ‘what’.

The acts of nature include, but are not limited to, lightning which will strike the tree directly, sending current from the top to the bottom of the tree or indirectly hitting the tree near enough to get affected. At times a single stroke of lightning can heat the air around it to 30 000°C, so in cases of lightning strike the tree will essentially be killed by the electric current and heat. Natural fires can also lead to the death of some trees, more specifically trees whose bark system has been destroyed by the flames but the inner support structure of the tree remains intact. In addition fires burning under the surface of the soil can destroy root systems which will kill the tree. During the dry season most trees will stop supplying water to the leaves to save water to aid in the survival of the rest of the tree, and leaves will start falling off. If a drought comes and the expected rain doesn't arrive most of these types of trees will start drying up. Drought also causes changes in ground water level, specifically dropping the ground water levels causing the death of trees.

Dead leadwood tree at sunset

There are a number of plants that cause the death of trees, such as creepers that creep up to the top of the tree trunk. Once they reach the canopy of the tree they begin to spread out and grow to an extent where their own leaf canopy covers the host leaf canopy, blocking it of any sunlight which leads to the death of that tree. Strangler figs do a similar thing beginning their journey as seeds on the top of the tree top and, as they grow, their root systems descend on the host trunk, eventually outcompeting with the host tree in a parasitic manner where they outcompete for the soil nutrients, water, and the sunlight as their tree canopy gets larger, but also, as its name suggests, its roots begin constricting/strangling the hosts trunk, leading to its death.

The death of trees in a natural system is nothing to mourn as it is very important to have dead trees in an ecosystem because many animals and plants make use of these dead trees to aid in their survival, such as big birds that specifically perch/roost on these dead trees, birds like eagles, storks and vultures who enjoy the convenience of being able to land and take off from them easily and the great 360 degree visibility they give. Termites and borer beetles feed on these dead decomposing trees. Some orchids grow on them. They are used as a rubbing post for many animals.

And over all the reduction of the tree numbers in this area keeps the habitat balanced ensuring these trees do not “over run” this type of habitat which could lead to these unchallenged trees growing into maturity, and if unchallenged their canopies would block out the sun rays from reaching the grasses and shrubs that are left in their shadows, which would mean the death of those sun-loving shrubs and grasses. In turn animals relying on feeding on those shrubs and grasses would move off, changing the biodiverse ecosystem.

All of these elements acting on the death of trees are playing a niche role in maintaining this environment as we know it, which allows us to enjoy the diversity that it offers.

By Walter Mabilane
Field Guide