Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Master → Afrique du Sud → 2010 → The effects of browsing on growth, structure and physiological aspects of Acacia grandicornuta and Combretum apiculatum

University of Zululand (2010)

The effects of browsing on growth, structure and physiological aspects of Acacia grandicornuta and Combretum apiculatum

Mamashela, Charlotte Thandeka

Titre : The effects of browsing on growth, structure and physiological aspects of Acacia grandicornuta and Combretum apiculatum

Auteur : Mamashela, Charlotte Thandeka

Université de soutenance : University of Zululand

Grade : MASTER OF SCIENCE (BOTANY) 2010

Résumé partiel
Very little is known about plants growing in savannas, especially how woody plants respond to browsing and variations in resources. It is assumed that growth rate and concentrations of defenses are inversely related, but will be affected by resource availability. It can be postulated further that increased growth and photosynthesis would be observed concomitant with reduced tannin concentration when water and nutrients are abundant at the beginning of the wet season. Growth in terms of shoots length, thorn length and plant height would increase in terms of increasing photosynthetic rate on browsed plants compared to unbrowsed plants. Therefore, research was conducted to investigate the effects of browsing on Acacia grandicornuta and Combretum apiculatum. Research was conducted at the Nkuhlu experimental exclosures (Kruger National Park) on these two tree species. The exclosures were designed so that there were three broad levels of browsing pressure : no mammal herbivores excluded, elephants and giraffes excluded and all mammal herbivores bigger than hares excluded, all of which incorporate the catena from sodic footslope to sandy crests. The focus was on heavily browsed plants between the heights of 0.7-1.7 m. Ten trees per species per treatment (full, partial and no exclosure) were sampled and height and stem circumference were measured in the early and late wet season. Five new shoots per tree were marked ; these shoots were re-measured at intervals to monitor their growth. Leaves were harvested from other short trees of both species in all the exclosures. Leaves were dried, milled and analysed for phosphorus (P), nitrogen (N) and condensed tannins (CT). Photosynthetic measurements were also recorded at the same time from short individual trees of C. apiculatum from the full and non exclosure. The results showed that there were no significant effects of the treatments and no significant growth on shoot and thorn length of A. grandicornuta in all the treatments from October to December 2007. There was significant growth in the shoot lengths of C. apiculatum from October to December 2007 in all the treatments (full exclosure t = -4.65, df = 10.20 and P = 0.001, non exclosure t = - 4.67, df = 7.90 and partial exclosure t = - 8.86, df = 7.30 There was a significant effect of the treatments on the shoot lengths of C. apiculatum during December 2007. There was no significant growth in heights and stem circumference of A. grandicornuta from September 2007 and March 2008 There was significant growth in the height of C. apiculatum in the full exclosure (t =2.33, df = 17.10 and the stem circumference of C. apiculatum was significantly smaller in the partial exclosure (t =3.71, df =8.00 September 2007 compared to March 2008. The pattern for both A. grandicornuta and C. apiculatum in all the treatments was a decreasing P concentration from October 2007 to March 2008. Nitrogen decreased in A. grandicornuta where mammals were excluded and also decreased in the non exclosure. In the partial exclosure there was no change in N concentration from October 2007 to March 2008. For C. apiculatum, N concentration decreased in all the treatments from October 2007 to March 2008.

Présentation

Version intégrale (1 Mb)

Page publiée le 11 mars 2011, mise à jour le 27 mars 2020