Kruger Park Econews | How are the personal lives of trees affected by elephants?

From germination to death, how does a particular tree species cope with the hazards of life in a savanna environment filled with elephants? Kruger’s scientific services have launched an ambitious new initiative that will contribute to the elephant management debate – but this time from the perspective of what goes on in the personal lives of the trees in the park. Does a particular species of tree produce a lot of babies (seeds) in its lifetime? Are the babies picky, only thriving in perfect soils and high rainfall, or are they happy to flourish in all soils and weathers?

Does the tree fight back when picked on by herbivores by filling its leaves with nasty-tasting chemicals? Does it roll over and die when a branch is broken off, or does it produce lots more shoots out of the wound in defiance of destruction? Is the tree simply a sour character from the time its first leaves poke out the ground, making elephants strike it off the menu? Of course, the questions the scientists are asking are not couched in quite those terms, but they deal with those sorts of issues. Kruger wants to know about the private lives of some 507 species of tree, shrub, liana and succulent that occur in the park, so that they can judge their vulnerability to local extinction as a result of elephant utilisation.

The first steps in this ambitious task were recently taken at a workshop held in Skukuza. In an initiative led by Dr Rina Grant, Kruger has teamed up with renowned savanna ecologist Prof Tim O’Connor to create a profile of all Kruger’s woody plants by using the known characteristics of the tree, how it grows and how often elephants select it as a food source. The task is not a simple one, and it is likely to take a long time to fill in all the blanks for more than 500 species. An obvious first stop is the scientific literature, looking for any information that has previously been recorded. The researchers also plan on picking the brains of everyone from field rangers to professors of botany with side trips into the minds of traditional healers.

Two post graduate student volunteers, Lindy Thompson and Michal Zrust, have already started picking the brain of someone who knows all about the reproduction of Kruger’s trees – the green-fingered Ona Davies who runs the Skukuza nursery. Ona has grown thousands of Kruger’s woody plants from seeds collected in the park, and she knows which plants grow fast or slow, which produce lots of seeds, which you need to plant a hundred seeds for in the hopes of a single germination, which are vulnerable to insect attack, and a mountain of other useful information.

However, what grows well in the nursery is not always the same as what grows well in the veld, so there will also be a strong field component in the research. Along with knowing how woody plants cope with elephants, the researchers also need to know about their distribution in the park. A tree might be very tasty to an elephant but if it mostly grows in places where elephants can’t reach, like the top of hills, then it is not likely to be as vulnerable to local extinction by elephants. Each of the 500 plus species will be rated according to how often the leaves or shoots are eaten; how easily it can be ringbarked or pushed over; how it recovers from any damage; how many adult trees die as a result of being pushed over or debarked; how well the plant grows from seed and how fast it grows; and how well is the plant protected in the area where it grows.

Depending on how all these factors combine will give a measure of vulnerability for each species, and point out which species need to be looked at more closely. Preliminary findings will be presented next January at an ecosystem modelling workshop being held in Skukuza.