Browsing by Author "Bond, W J"

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    Seed development, morphology and quality testing in selected species of the nut-fruited Restionaceae
    (Elsevier, 2002) Newton, R J; Bond, W J; Farrant, J M
    Seed germination is poor in species of the nut-fruited Restionaceae. Investigations of seed morphology and development, seed collection and sorting, and seed viability were conducted in species of Cannomois Desv., Hypodiscus Nees and Willdenowia Thunb. to supplement existing knowledge, and to determine whether poor seed quality resulted in the poor seed germination identified in previous studies. Suitability of collection methods and the effectiveness of sorting techniques were evaluated using x-radiography. Shaking and ground collection methods yielded consistently higher proportions of full seed than extracting seed from cut shoots. However in species with bony bracts and few seeds per plant, the cutting method was more suitable. Floating was a better seed sorting technique than weighing for separating full from incompletely filled seeds. Seed viability in seed collections that had been sorted to contain only fully developed seeds was assessed using tetrazolium salts. Viability was generally high (mostly >80%), suggesting that poor germination in studies with well-sorted seeds is likely to be due to seed dormancy.
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    What controls South African vegetation - climate or fire?
    (2003) Bond, W J; Midgley, G F; Woodward, F I
    The role of fire in determining biome distribution in South Africa has long been debated. Acocks labelled veld types that he thought were ‘fire climax’ as ‘false’. He hypothesised that their current extent was due to extensive forest clearance by Iron Age farmers. We tested the relative importance of fire and climate in determining ecosystem characteristics by simulating potential vegetation of South Africa with and without fire using a Dynamic Global Vegetation Model (DGVM). The simulations suggest that most of the eastern half of the country could support much higher stem biomass without fire and that the vegetation would be dominated by trees instead of grasses. Fynbos regions in mesic winter rainfall areas would also become tree dominated. We collated results of long term fire exclusion studies to further test the relative importance of fire and climate. These show that grassy ecosystems with rainfall > 650mm tend towards fire-sensitive forests with fire excluded. Areas below 650mm showed changes in tree density and size but no trend of changing composition to forest. We discuss recent evidence that C4 grasslands first appeared between 6 and 8M years BP, long before the appearance of modern humans. However these grassy ecosystems are among the most recently developed biomes on the planet. We briefly discuss the importance of fire in promoting their spread in the late Tertiary.
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    Will water abstraction from the Table Mountain Aquifer threaten endemic species? A case study at Cape Point, Cape Town
    (2004) February, E C; Bond, W J; Taylor, R; Newton, R
    THE PRINCIPAL SOURCE OF CAPE TOWN’S future water needs is the Table Mountain Group aquifer. The floral characteristics of the region overlying this aquifer are unique with five endemic and one near-endemic families. Many of these endemics are restricted to areas such as wetlands and marshes that are supplied by aquifer water, making them vulnerable to groundwater abstraction. Here we report the results of a study undertaken at two sites in the Cape Point Nature Reserve using stable hydrogen isotopes to determine the water source of plants to establish dependence on a permanent water supply. The results from the Suurdam site suggest that Erica labialis has a more diverse rooting strategy than Erica multumbellifera, with two plants sourcing water close to the surface, whereas others extract water much deeper down. The results from the Anvil Hill site, however, suggest that the rare Mimetes hirtus uses water very close to the surface that has undergone extensive isotopic fractionation. These results indicate that this species is shallow-rooted and dependent on surface soil water for survival. As such, it would be vulnerable to an even slight lowering of the water table during the dry summer months, when the surface soil water would be replenished mainly from the permanently saturated zone of the wetland. These results have implications for other endemic plant families with the same water requirements.