Changes in rainfall pattern in the eastern Karoo, South Africa, over the past 123 years

Rainfall is a key driver of ecosystem processes, especially vegetation dynamics, in semi-arid regions. Rainfall amount, including droughts and extended wet periods, seasonality, and, possibly, concentration, influence vegetation composition in the eastern Karoo. A monthly rainfall record of 123 years from Grootfontein was analysed to search for evidence of cyclicity in rainfall amount, seasonality, and concentration. Rainfall was substantially higher during the late 1800s and after 1990 than it was during the rest of the 20th century. Extended sequential below-average runs of years characterised the drought periods of the early 20th century and the 1960s. There was strong evidence of an approximately 20-year rainfall cycle, except for spring rain. Additionally, annual and seasonal rainfall showed evidence of a longer cycle, between 44 and 77 years, which may be related to the southern oscillation index. The additive effects of the two cycles described annual and seasonal rainfall with R2 values typically > 0.5. Rainfall seasonality was also related to the longer-term cycle, while rainfall concentration showed some evidence of having entered a new, more concentrated state since 1988. The analysis reveals that rainfall at Grootfontein is not a random process, but rather appears driven by cyclical processes. Rainfall at the site is predicted to decline over the next approximately 20 years, and the high levels of variation and complex causal factors will make it difficult to discriminate between natural variation and possible effects of climate change on rainfall.Keywords: semi-arid, rainfall concentration, rainfall seasonality, periodicity, cyclicit

Research NoteEarly survival and growth of vegetatively propagated indigenous grasses in a clear-felled timber plantation in KwaZulu-Natal, South Africa

Transformation of natural landscapes can result in the local extinction of many plant species. If the new land use is discontinued, many original species will not recolonise the area, necessitating their reintroduction for rehabilitation purposes. One method is to fragment local grass tufts into tillers and plant these into the degraded area. This project determined the survival and growth rates of various grass species planted into a recently cleared pine plantation near Nottingham Road, South Africa. Tufts of twelve grass species were collected locally, fragmented, kept on a mist bed for four weeks, and planted. Plants from all species were alive after nine months, although the average survival rate varied between species (from 92% for Eragrostis curvula to 39% for E. racemosa). Tuft area differed between species. The often-invasive species E. curvula had the highest average survival rate and the largest tuft area. The often-dominant, unpalatable Aristida junciformis demonstrated surprisingly low survival and growth rates. Themeda triandra and Tristachya leucothrix, species often dominating good-condition native grasslands, had average survival rates of 82% and 65%, respectively. This study indicates that tuft fragmentation and replanting is a useful way to re-establish locally extinct grass species into transformed habitats,  but that success rates are species-specific. African Journal of Range & Forage Science 2009, 26(2): 97–10

Research NoteSpecies/defoliation/drought interactions on tuft survival and tiller and phytomass production in four sourveld grass species in KwaZulu-Natal, South Africa

Productivity and mortality of grass plants following drought may be controlled by interactions between defoliation and severity of the drought. Prudent grassland management might mitigate deleterious changes in species composition in multispecies grasslands. This study, conducted in a horticultural tunnel, explored the interactions of drought duration, and the period of uninterrupted postdrought growth before defoliation, on phytomass, tiller production and mortality of Aristida junciformis, Eragrostis curvula, Hyparrhenia hirta and Themeda triandra. Pretreatment tiller production was highest for Aristida and Eragrostis, followed by Hyparrhenia and then Themeda. Mortality was positively related to tuft size and drought duration. Tiller mortality was controlled by a species × drought interaction and the covariate tuft-size. All species lost tillers following a 28-day drought, with the highest loss in Eragrostis and lowest in Themeda. Phytomass production was positively related to recovery, and inversely related to drought duration. Species-specific differences in production were apparent only in the no-drought treatment, where Hyparrhenia produced more phytomass than Themeda and Eragrostis. Aristida had the lowest phytomass production and showed little plasticity across drought treatments. Results indicated that postdrought rest is important for phytomass production, and that species may exhibit a tradeoff between productivity and survival.Keywords: fodder production; rehabilitation; tradeoff; water stressAfrican Journal of Range & Forage Science 2010, 27(1): 57–6

Research NoteTebuthiuron residues remain active in soil for at least eight years in a semi-arid grassland, South Africa

The non-selective, soil-applied herbicide tebuthiuron (1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea) is registered for the control of the indigenous encroacher shrub Seriphium plumosum (Asteraceae) in South Africa. The use of tebuthiuron on a farm in the Cymbopogon–Themeda  veld type in the Zastron district of the Free State has led to the formation of bare patches in the grass layer. This study investigated patterns of emergence and survival of monocotyledonous oats (Avena sativa) and dicotyledonous cabbage (Brassica oleracea) in soils collected from bare patches resulting from the application of tebuthiuron between two and eight years earlier. Untreated soils provided a control. Both oats and cabbage emergence was high and not related to herbicide application. After about two weeks, plants growing in tebuthiuron-treated soil began to die, and after 60 d only four of the 299 emerged seedlings were alive, but showed signs of mortal phytotoxicity. Mortality in the control was low. It was concluded that tebuthiuron residues in the bare patches may preclude recolonisation by seed for at least eight years  following application.African Journal of Range & Forage Science 2012, 29(2): 85–9