The influence of rainfall variability on savanna tree seedling establishment

My thesis investigates the rainfall requirements necessary for tree seedling survival of different savanna species in the first year of growth. Results from a field drought experiment showed that dry season survival for seedlings of Acacia nigrescens and Philenaptera vialacea was not related to wet season length. Instead mortality was highest immediately after germination despite irrigation to minimize dry spells. Furthermore there was no relationship between seedling size and the length of the dry spell seedlings of Acacia nigrescens and Philenaptera vialacea grown in basalt clay in the greenhouse, could survive. This was in contrast to seedlings of Scleracarya birrea and Terminalia sericea grown in granite sand, where number of dry days survived increased with number of growth days received. There was no significant differences in rainfall variability (t-test: tL III = 1.56, P = 0.121, F-ratio = 1.13) between a semi-arid (Satara) and semi-mesic (Pretoriuskop) site within the Kruger National Park despite significant differences in rainfall totals (t-test: tl, III = 4.40, P < 0.000, F-ratio 3.41). Results from a soil-water model show that seedling recruitment can occur at least twice a decade in the Satara area, which should be frequent enough to allow a transition to a woodland state over time. These results suggest that a mechanism other than the effect of rainfall variability on seedling establishment is required to explain the co-existence of trees and grasses at Satara. The lack of field germination, the absence of a seed bank and the germination of added seed at the field experiment site after rainfall emphasizes seed limitation as an important bottleneck at Satara. Higher herbivore biomass at Satara compared to Pretoriuskop may limit seedling establishment opportunities by destroying seed and seedlings of tree species.

Grantor dc:publisher.institution

Department of Biological Sciences

Year dc:date.issued

2006

Author dc:creator

• Botha, Susan

Advisors dc:contributor.advisor

• Bond, William J
• February, Edmund C

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/6238

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/6238