Response of marula to simulated browsing on a productivity gradient
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Date
2015
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University of Zululand
Abstract
Marula (Sclerocarya birrea) is a heavily utilisedsavannah tree species and is widely used by people and animals for its leaves, bark, fruits and roots. Because of its importance in terms of economy, ecology, cultural values and dominance in some low veld areas of South Africa, it is therefore of importance to understand responses of marula trees to environmental factors. Two key factors in regulating savannah functioning are browsing and soil fertility. The aim of this research was to assess the effects of simulated browsing on the physical and chemical properties of marula trees growing on a productivity gradient in a controlled environment. The hypothesis to be tested was that, marula saplings respond to browsing intensity by showing a trend of increasing treee height, stem diameter, old shoot extension, number of new shoots, new shoot length, leaf biomass and foliar nitrogen along a productivity gradient. Conversely, marula saplings showed a trend of decreasing flavonoid content, condensed tannin concentration, Neutral-detergent fibre, acid-detergent fibre, and acid-detergent lignin in response to to increasing browsing intensity along a productivity gradient. Browsing was simulated bu clipping the saplings at a range of intensities and a productivity gradient was achieved by applying fertiliser at a range of levels. The interaction between clipping and fertiliser treatments had a significant effect in explaining final tree heigh (P<0.001), stem diameter (P<0,001), old shoot extension (P=0.028), and number of new shoots (P=0.040) but the significance of the interaction for final tree height and stem diameter was influenced by both initial tree height and initial stem diameter as covariates. New shoot length and leaf biomass were significantly influenced by fertiliser and clippings separately not by their interaction (P=0.005, P=0.001; P=0.043, P,0.001) respectively. Clipping treatment significantly influenced ADL at the end of the experimental period (P=0.048). None of the studied fixed factors significantly influenced N, flavonoids, CT, NDF, and ADF at the end of the experiment. Marula saplings growing along a productivity gradient tend to compensate by new shoot productivity (number and length) in response to intermediate clipping but this response did not reflect the compensatory ability of total aboveground biomass, because tree height and stem diameter were not increased. Severe clippings and defoliation treatment induced defence responses regardless of fertiliser rates, thus suggesting carbon limitations. The results from this study also indicated that physical responses nto a single clipping event persist for longer than chemical responses do.
Description
A thesis submitted to the Faculty of Science and Agriculture in fulfillment of the requirements for the Degree of MSc (Agriculture, Animal Science) in the Department of Agriculture at the University of Zululand, 2015
Keywords
carbon-based secondary mrtabolites --Sclerocarya birrea, condensed tannins --growth --herbivory --plant defences