How do Tree Seedlings Survive all the Hungry Herbivores

SCI volunteers fitting mesh cage around marula seedling.
? Georgette Lagendijk

By Michele Hofmeyr

Trees produce countless thousands of seeds over the years but do all of these seeds grow into trees? Georgette Lagendijk, PhD student from the school of biological and conservation sciences at the University of KwaZulu-Natal in Durban is busy investigating whether browsing antelope (like impala and kudu) are eating the young seedlings as they start to grow and if this is having an effect on the survival and growth of particular tree species. Trees under the spotlight include the distinctive bushveld marula (Sclerocarya birrea), knobthorn (Acacia nigrescens) and buffalo-thorn (Ziziphus mucronata).

Using a detailed field experiment Georgette has been planting out seedlings of the selected species in the Greater Makalali Private Game Reserve (GMPGR). This 24,000 hectare reserve is situated in the central Lowveld region of the Limpopo Province, close to the Kruger National Park.

With the fantastic help of volunteers, from the Siyafunda Conservation Initiative (SCI) based in GMPGR, the immense task of planting out the 450 seedlings was certainly made easier.

As part of the experimental design, certain seedlings are protected from hungry herbivores by wire mesh cages. This is because Georgette needs to compare the amount of browsing the unprotected seedlings experience with the seedlings inside the mesh cages.

To make sure the young seedlings survive being out in the veld, each of them will be watered initially to make sure they keep on growing. To see if there are any herbivores in the area, a few small plots will be cleared to see what spoor are left behind and additional dung counts will be done in the area. Herbivores may often move through the veld but may not be seen, so spoor and dung counts give an idea of numbers of animals in an area.

The unprotected seedlings in the veld will be frequently monitored to see how many of them are being eaten or damaged. With time it will be possible to see how they cope with being a green leafy snack that is potentially very attractive to a hungry herbivore.

Over the next year Georgette hopes to unravel some of the mysteries of how small seedlings manage to grow into our most favourite bushveld trees.



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