Browsing by Author "Burger, Niel"

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    Disturbance ecology and size class structure of the Mulanje cedar of Malawi, Widdringtonia whytei and associated broadleaved forest
    (2010) Burger, Niel; February, Edmund C
    The disturbance ecology and regeneration patterns of the emergent conifer, Widdringtonia whytei, and five broadleaved species, Aphloia theiformis, Rapanea melanophloeos, Maesa lanceolata, Maytenus accuminata and Psychotria mahonii, were inferred from population size structures in the mixed conifer-broadleaved forests of Mt. Mulanje, Malawi. The size-class structures of the emergent cedar populations were characterised by even-sized, disjunct frequency distributions. Seedling recruitment was found in recently burnt sites and not in middle-aged or oldgrowth forest. This indicates reliance on the catastrophic mode of regeneration for W. whytei, which takes advantage of the well-lit, competition free environment after large-scale disturbances provided by fire. The sub-canopy angiosperms primarily had all-sized frequency distributions, with at least some individuals found in each class within their size range, indicating continuous regeneration under a closed forest canopy. These results emphasize the dependence of long-lived conifers such as the Mulanje cedar on large-scale disturbance for regeneration and long-term persistence of the species.
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    Flammability traits of fynbos species with different post-fire regeneration strategies
    (2010) Burger, Niel; February, Edmund C
    Wild fire is an important disturbance regime that shape global biome distributions and maintain the structure, function and biological diversity of plant communities in fire-prone environments. Physical, chemical and architectural properties are known to affect plant flammability, but few studies explore how these traits contribute to fire properties at the individual level and how flammability is influence by regeneration strategy. The flammability and traits that contribute to it is investigated in 15 co-occurring fynbos and forest species with burning experiments performed at Bain's Kloof Pass, Western Cape of South Africa. Eight species are characterised by fire-stimulated (mostly seeders) and seven by non-fire-stimulated recruitment (mostly resprouters). Results across all species are consistent with other studies which indicate that the proportion of dead and fine fuel is significant predictors of flammability. Significantly higher flame temperatures and values for % fuel burned were recorded for FSR's relative to NFSR's and these differences are attributed to significant differences in % fuel dead, fuel bed porosity and packing ratio. This is consistent with the hypothesis that flammability is most like to be selected for in fire-stimulated recruiters (first colonisers after fire) where a combination of increased flammability and recurrent success enhance their fitness in the fire-prone environment. This study indicates that cultivation of the highly flammable species E. rhinocerotis, Stoebe sp., M. muricata, Erica sp. and P. amplexicaulus on urban fringes should avoided to reduce fire-risk and thus increase human safety.