Browsing by Author "February, E C"

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    A dendrochronological assessment of two South African Widdiringtonia species
    (Elsevier, 2003) February, E C; Gagen, M
    In southern Africa long-term regional rainfall data sets are very limited such that the variability of rainfall across the region is poorly understood. With available climate records so limited the development of strong proxy records are vital to develop drought management plans. In our continuing efforts to develop such proxy records we present the results of an investigation into the dendrochronological potential of Widdringtonia nodiflora and Widdringtonia schwarzii. We sampled W. schwarzii, from the area it is endemic to, the Baviaanskloof wilderness area, in the Langkloof region of the Eastern Cape Province. Widdringtonia nodiflora samples were collected from the Grootvadersbosch Nature Reserve near Heidelberg in the Western Cape Province. The results indicate that inconsistencies in ring width combined with poorly defined ring boundaries and converging rings make cross-dating between different trees from the same locality an impossible task for both species using manageable sample numbers. Without cross-dating, chronology development is an equally impossible task for both W. nodiflora and W. schwarzii. As with W. cedarbergensis, W. schwarzii may avoid drought stress by accessing deep water. This may explain the many false rings and poorly defined ring boundaries apparent in this species. This study concludes the dendrochronological assessment of all of the Widdringtonia species with only two South African conifers not evaluated (Podocarpus henkelii and P. elongatus). Widdringtonia cedarbergensis is the only South African conifer that has been successfully cross- dated, however, there are no significant correlations between ring width indices and climate variables for this species.
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    Open Access
    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.