Pretoria, South Africa
Pretoria, South Africa

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Granger J.E.,SAEON | Granger J.E.,Knight Piesold Pty Ltd | O'Connor T.G.,SAEON | O'Connor T.G.,University of Witwatersrand
African Journal of Range and Forage Science | Year: 2015

Mining for copper and cobalt generates extensive mounds of removed topsoil and subsoil, and tailings with toxic levels of copper and cobalt. The threat of soil erosion in a high rainfall regime can be countered with rapid establishment of a sod-forming grass, such as Cynodon dactylon, that covers and binds the soil. An experiment was initiated in early 2013 to investigate whether planting vegetative material (plugs) was more effective than sowing of seed, and whether soil amelioration (fertilisation) was necessary on a substrate-specific basis. The experiment was assessed at the end of May 2013. Aerial vegetative cover was correlated with above-ground dry mass. Planting of plugs in combination with fertilisation was overall the most effective. On tailings, seed without fertilisation was a complete failure and fertilisation was essential for growth of plugs. Fertilised plugs resulted in a high density of stolons but fertilised seeds did not, although the response was delayed on tailings. Once phyto-stabilisation has been achieved, C. dactylon might serve as a nursery bed for establishing locally adapted cuprophytes of conservation significance. © 2015 NISC (Pty) Ltd.

O'Connor T.G.,SAEON | O'Connor T.G.,University of Witwatersrand | Page B.R.,University of KwaZulu - Natal
Biological Conservation | Year: 2014

Elephant populations at high density commonly transform their habitat, but a low density population would not be expected to have a marked impact. Re-introduction of elephants into the Venetia-Limpopo Nature Reserve (320km2) in the early 1990s established a low density population for the period of survey (0.16-0.33 individuals km-2). Accordingly, their impact on the composition and structure of the woody vegetation of three riparian and nine dryland vegetation types was measured between 1997 and 2010 using 148 permanent transects. Riparian habitat showed a greater change in composition and diversity, and also a greater decline of species richness, density of tall trees or total basal area, than dryland habitat. Change of dryland Commiphora Woodland was comparable to changes of riparian types. These conspicuous changes were a consequence primarily of severe use by elephants. Some species within these vegetation types declined markedly in abundance. Vegetation types dominated by Colophospermum mopane showed an increase in total basal area and relatively minor change in composition or structure, resulting mainly from the impact of moisture stress. Vegetation types that were severely impacted by elephants constituted <10% of reserve area; lightly impacted dryland C. mopane types constituted >70% of area. Some uncommon, selected dryland species were heavily impacted by elephants. A number of species may therefore be trending toward local extirpation. It was concluded that the coexistence of elephants and some plant species in this medium-sized, contained reserve was not possible. © 2014 Elsevier Ltd.

du Toit J.C.O.,Grootfontein Agricultural Development Institute | O'Connor T.G.,SAEON
Transactions of the Royal Society of South Africa | Year: 2016

Minimum temperatures and frost are ecologically and agriculturally important parameters as they can cause mortality in plants and livestock, shape the position of biome boundaries, influence the lifecycles of pests and diseases, and influence the availability and quality of livestock feed. This study examines minimum temperature data from 1916 to 2014 for a site on the Nama-Karoo/Grassland biome ecotone. Temperatures of at least −6 °C occur almost every year, while temperatures of below −10 °C occurred in 15 of the years on record. Temperature data did not exhibit a random pattern, but rather showed the period from 1935 to 1960 to be particularly cold in terms of absolute minimum temperatures, the probability of occurrence of frost and the duration of the dormant (frost) season. The results provide a platform for interpretation for ecological and agricultural processes that have been recorded in several long-term trials at Grootfontein. The patterns of variation in the data indicate that short (c. 50-year) temperature datasets may give misleading indications in trends in temperature, and for an empirically-based interpretation of climate change, long-term datasets of approximately a hundred years are needed. © 2016 Royal Society of South Africa

Everson C.S.,SAEON | Everson T.,University of KwaZulu - Natal
African Journal of Range and Forage Science | Year: 2016

Natural grasslands deliver essential ecosystem services through plant production, which enhances water supply, nutrient cycling, soil retention and greenhouse gas mitigation. Although the condition of montane grasslands for provision of ecosystem services is maintained by regular annual or biennial burning, controversy exists over the impact of different frequencies and seasons of burning on grassland productivity. The objective of this study was to determine the long-term effects of different burning regimes on primary production and quality of the montane grasslands of the KwaZulu-Natal Drakensberg. There were no significant differences in the mean standing live mass between 30 years of annual winter and biennial spring burning. However, in unburnt areas productivity was 20% lower (118.2 g m−2) than in regularly burnt grassland (144.7–154.5 g m−2). Crude protein did not vary between the annual winter and biennial spring treatments (95–113 kg ha−1), but was significantly lower in unburned areas (45 kg ha−1). However, an infrequent fire in a protected area caused a temporary spike in crude protein (16%) compared with regular burning (5–10%), which can benefit wildlife. We conclude that montane grasslands can be burnt annually or biennially in the dormant season to promote long-term productivity. © 2016 NISC (Pty) Ltd

O'Connor T.G.,SAEON | Kuyler P.,University of the Free State | Kirkman K.P.,University of KwaZulu - Natal | Corcoran B.,World Wildlife Fund
African Journal of Range and Forage Science | Year: 2010

The relative benefit of different grazing management practices for maintaining grassland biodiversity integrity was assessed. Practices considered were grazing system, stocking rate, animal type, grazing season, fire-grazing interaction, plus burning regime. Sparse empirical data indicated that stocking rate, cattle-to-sheep ratio, and increased fire intervals can affect plant diversity. Certain species behave as increaser or decreaser species in response to stocking rate or cattle-to-sheep ratio. Plant diversity appears robust in the face of variation in fire regime except for preclusion of fire. Multicriteria analysis was used to assess the relative impact of grazing systems (continuous, conventional, or high-intensity grazing by sheep, cattle, or sheep plus cattle) on grassland biodiversity integrity. Selected indicators covered landscape composition, structure and functioning. High-intensity systems and continuous sheep grazing have the most, and continuous grazing with beef the least, negative impact, depending on stocking rate. The relation between veld condition and plant diversity needs to be tested further before veld condition is used as a management tool for maintaining biodiversity. Proposed research priorities include inventory of management systems used, rapid expansion of the empirical data base, an improved understanding of patterns of plant diversity across the biome, and evaluation of the pyro-grazing diversity paradigm. © NISC (Pty) Ltd.

Canopy tree survival and compositional change of the Greefswald forest on the Limpopo River, South Africa, were monitored between 1990 and 2007 in response to a severe drought (cessation of flow in 1991/2), water abstraction commencing in 1991, a mega-flood in 2000 and increasing impact of elephants since 2000. Aerial photographs confirmed that forest area had not decreased during the 35-years prior to the study. In total, 25% of 428 canopy trees tagged in 1990 had died by 2005. Tree density was reduced from 22.8 to 16.3 trees per hectare. Forest was thus transformed to woodland. Mortality was attributed mainly to drought stress (47%), drought in combination with creeper infestation (30%) and the flood (21%). Of the nine main canopy species, mortality was highest for Acacia xanthophloea (56%) and Faidherbia albida (37%) mainly because of drought-related stress, and Ficus sycamorus (25%) mainly because of the flood. Water extraction increased drought-related mortality in the area of extraction by 45%. Creepers rendered microphyllous but not broad-leafed species more vulnerable to drought-induced mortality. Elephants were responsible for a further 3% mortality between 2005 and 2007. Composition has shifted towards 'drought-tolerant' species not selected by elephants, namely Philenoptera violacea, Xanthocercis zambesiaca and Schotia brachypetala. Initial concern about water abstraction was eclipsed by a rapid, unpredictable concatenation of a series of rare events that transformed forest to woodland in less than 15-years. © 2009 The Author. Journal compilation © 2009 Ecological Society of Australia.

O'Connor T.G.,SAEON | O'Connor T.G.,Dohne Agricultural Development Institute | de Ridder C.H.,Dohne Agricultural Development Institute | Hobson F.O.,Dohne Agricultural Development Institute
African Journal of Range and Forage Science | Year: 2010

Seed ecology may play a role in the widespread increase of Acacia karroo in savanna and grassland. Accordingly, fecundity, predation, mortality by fire, dispersal by livestock, and seed longevity were studied. Seed production per tree (P of pod production, pods per tree) was positively related to tree height, negatively related to tree density, and was greater for sites receiving run-on. Predispersal predation by bruchids, cerambycids, and wasps depleted seed production by 18%. The ant Messor capensis effectively eliminated surface seed except during the early dry season following seed shed. Rodent predation of seed was minimal. Fires >100 °C killed most exposed seed but a thin layer of soil increased survival and maintained germinability. A greater proportion of ingested seeds passed through cattle (57%) and sheep (50%) than through goats (15%). 50% of seeds were recovered within 48 h. During passage, soft seeds were digested, some hard seeds were softened, but most were egested as hard seeds; germinability was not increased. Cattle were confirmed as dispersal agents. Using experimental seed banks, it was shown that buried or surface-exposed seeds did not persist for longer than a year, but 24% of surface-shaded seeds persisted for two years. Most seeds germinated but most buried seeds died before emergence. Seed persistence in deep shade should facilitate invasion into grassland. Seed banks of A. karroo did not exceed 18 seeds m -2 because of the above-described effects. Seed availability (fecundity, dispersal by cattle, seed longevity) is concluded to contribute to the invasiveness of A. karroo, but use of fire may offer partial control of seed availability. © NISC (Pty) Ltd.

Reduced grazing pressure is expected to promote recovery of degraded semi-arid savanna. Transformation of degraded livestock ranches to a wildlife reserve in 1982 created a system with about one-third of the grazing pressure, which was maintained until 2011. Herbaceous composition and condition were monitored on four occasions between 1982 and 2011. Baseline measurements were taken following eight years of above-average rainfall conditions. Palatable perennial grasses and sward condition deteriorated markedly in response to severe, sustained drought during the early 1990s. Perennial grasses did not respond to a single record high rainfall season (2000) but recovered following a sequence of four above-average years (2008–2011). This monitoring study illustrated that recovery of a degraded semi-arid savanna may require decades of reduced grazing pressure for some degree of recovery in the absence of intervention. An appropriate time frame for management of these systems is in the order of a century. © 2015 NISC (Pty) Ltd.

O'Connor T.G.,SAEON | Chamane S.C.,SAEON
African Journal of Range and Forage Science | Year: 2012

Bush encroachment is a vegetation dynamic of global interest. This study describes the pattern of succession of bush clumps in the Eastern Cape, South Africa, using a space-for-time substitution. Clumps formed following establishment of mainly Acacia karroo in grassland through nucleation via animal dispersal. A total of 49 tree or shrub species were recorded in 40 clumps. With increasing clump size, there was a corresponding increase in woody basal area, species richness and diversity, but not evenness. Correspondence analysis showed that the pattern of compositional variation was closely related to clump size; differences resulting from clump establishment disappeared as clumps developed. Population size structure of 20 (of 21) species was dominated by small individuals, indicating that regeneration has increased over time. Coddia rudis was prolific on a clump periphery; Scutia myrtina and A. karroo were dominant within clumps. Seven shrub and nine tree species were encountered more frequently within a clump than on its periphery. All species other than A. karroo had fruits suited to dispersal by birds or mammals. The overall pattern of bush clump succession shows close parallels with that initiated by invasion of Prosopis glandulosa into grassland in Texas, USA. © 2012 Copyright NISC Pty Ltd.

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