Volume 14, Number 22: 1 June 2011
M.T. Hoffman of the University of Cape Town's Botany Department and R.F. Rohde of the University of Edinburgh's Centre of African Studies write that "global circulation models predict broad-scale habitat loss in the semi-arid winter rainfall region of southern Africa in the coming decades," citing Midgley et al. (2005), while noting that "several different 50-100 year climate change scenarios have been developed which suggest a 25% drop in winter rainfall and a 2°C rise in temperature, as well as significant drying during the winter and spring months in the semi-arid winter rainfall areas between the Kamiesberg mountains and the coast," citing Midgley et al. (2005) and McKellar et al. (2007). In addition, they report that "such predictions, coupled with niche-based modeling methods for plant species common to the succulent karoo biome, suggest that there will be a 40% reduction in the bioclimatically-suitable environment for most species by 2050," and that Musil et al. (2004) "have shown experimentally that plant mortality of succulent karoo species increases significantly with prolonged exposure to the kind of temperature regimes predicted under future climate change scenarios."
So what's been happening over the last several decades in the ill-fated part of South Africa? Has it been anything like what's been predicted to occur?
To find out, the two researchers reviewed a number of prior studies that assessed the extent of change in plant cover at 32 sites using historical photographs that covered a time span of 36-113 years, focusing on river systems and their associated riparian vegetation. This work provided, as they describe it, "little evidence that the vegetation cover has declined over time," citing the studies of Hoffman and Rohde (2007), Rohde and Hoffman (2008) and Hongslo et al. (2010). In fact, they report that "the observed trajectories of vegetation change recorded in these studies suggest that the historical trend in plant cover has been in the opposite direction to that which is suggested by the general aridification hypothesis proposed for the future (Midgley and Thuiller, 2007)," and they state that "vegetation cover has generally increased and not decreased over the course of the 20th century." More specifically, they indicate that in the majority of sites there has been a significant increase in the cover of riparian vegetation in both the channel beds of the region's rivers and adjacent floodplain environments, and they state that "the most important species to have increased in cover across the region is Acacia karroo."
Once again, therefore, climate alarmists appear to have widely missed the mark by way of their overly pessimistic prognostications.
Sherwood, Keith and Craig Idso
Hoffman , M.T. and Rohde, R.F. 2007. From pastoralism to tourism: The historical impact of changing land use practices in Namaqualand. Journal of Arid Environments 70: 641-658.
Hoffman, M.T. and Rohde, R.F. 2010. Landscape change and ecological processes in relation to land-use in Namaqualand, South Africa, 1939-2005. South African Geographical Journal 91: 63-74.
Hoffman, M.T. and Rohde, R.F. 2011. Rivers through time: Historical changes in the riparian vegetation of the semi-arid, winter rainfall region of South Africa in response to climate and land use. Journal of the History of Biology 44: 59-80.
McKellar, N.C., Hewitson, B.C. and Tadross, M.A. 2007. Namaqualand's climate: Recent historical changes and future scenarios. Journal of Arid Environments 70: 604-614.
Midgley, G.F., Chapman, R.A., Hewitson, B., Johnston, P., De Wit, M., Ziervogel, G., Mukheibir, P., Van Niekerk, I., Tadross, M., Van Wilgen, B.W., Kgope, B., Morant, P., Theron, A., Scholes, R.J. and Forsyth, G.G. 2005. A Status Quo, Vulnerability and Adaptation Assessment of the Physical and Socio-Economic Effects of Climate Change in the Western Cape. Report to the Western Cape Government, Cape Town, South Africa. Report No. ENV-S-C 2005-073. Stellenbosch: CSIR.
Midgley, G.F. and Thuiller, W. 2007. Could anthropogenic climate change threaten biodiversity in Namaqualand? Journal of Arid Environments 70: 615-628.
Musil, C.F., Schmiedel, U. and Midgley, G.F. 2004. Lethal effects of experimental warming approximating a future climate scenario on Southern African Quartz-Field Succulents: A pilot study. New Phytologist 165: 539-547.
Rhode, R.F. and Hoffman, M.T. 2008. One hundred years of separation: The historical ecology of a South African "Colored Reserve." Africa 78: 189-222.