Fertilising Bush Gives Sanparks Scientists Food For Thought

It is a dilemma that probably bothers the odd tourist to the Kruger National Park (KNP), has almost certainly bothered more than one elephant, and is currently at the forefront of a number of scientific minds. If you eat 180kg of vegetation each day, where on earth do you find it all, and what makes the nicest meal?

Perhaps more precisely, what the scientists have been asking relates to the distribution of elephants and other herbivores in conservation areas in relation to the nutrient status of the vegetation. Now they hope that Tembo can give them the answers. Tembo, or more specifically, The Elephant Movements and Bio-economic Optimality programme, is a five-year programme run jointly by the Wageningen University in the Netherlands and the University of Kwa-Zulu Natal.

The project is funded by WOTRO (a Dutch funding agency for research in the tropics). The main objective of the Tembo project is to predict the distribution of elephants in conservation areas in relation to the nutrient status of the vegetation, in order to carry out a cost-benefit analysis for the optimisation of resource management for commercial purposes and conservation.

Ecologists from Sanparks Scientific Services in the Kruger National Park visited the projects Tembo are currently running in the Timbavati Private Nature Reserve. The group was shown various sites by Cornelis van der Waal and Yolanda Pretorius, both Tembo PhD students working in the Timbavati. In the main experiment, various sized plots had been fertilised with three different levels of phosphorous and nitrogen from low to high concentrations. The size of the fertilised patches varies from 2x2m to 50x50m in size.

This experiment is conducted in an area of 30ha on the farm Sumatra in the Timbavati. The purpose of this study is to investigate how differences in soil nutrient availability (soil fertility) affect grass production and palatability or tastiness. These plots will also show the different responses of trees and grasses to fertiliser applied in small and large patches in the low nutrient mopane savannas.

The experiments will also look at the effect of fertilisation on the shoot growth and leaf numbers of mopane trees. The soil nutrients also influence the quality of the grass, which in turn will influence the types and numbers of animals that will come to the area to graze. The second site shown was an exclosure experiment where 1m x1.5m cages keep out herbivores from the fertilised patches of grass and make it possible to see the effect of fertilisation on grass production and utilisation. 

The preliminary results show that fertilisation increased grazing off-take more than 10 fold. A third project currently running in the Timbavati is looking at how animals utilise these fertilised patches. This research is being conducted by Yolanda Pretorius. This project will look at how foraging behaviour of small to large herbivores is affected by patch size and nutrient concentration. To do this, Yolanda is counting spoor and dung piles in cleared sand areas near fertilised patches, while also monitoring how long it takes for dung piles to decompose.

The results so far are showing that for the most abundant herbivore species in the area, larger animals such as buffalo select large fertilised patches while smaller herbivores like impala are more sensitive to local nutrient concentration. "It is very useful for us to see the results of these fertilisation experiments in reserves neighbouring the Kruger National Park" said Dr Rina Grant, systems ecologist for Scientific Services, based in Skukuza.

"We are interested in how nutrients affect the distribution of animals in our savanna systems and considerable information can be gained from detailed experiments such as these. We can use these findings to better understand changes in the system and build these into our monitoring programmes that in turn inform management plans" explained Dr Grant.

By Michele Hofmeyr and Raymond Travers

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