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South African Journal of Botany 2003, 69:1–6
Copyright© NISC Pty Ltd, www.nisc.co.za
‘Enough to be considered useful’: John Acocks’ contribution to South African botany
MT Hoffman1* and RM Cowling2
1 Institute for Plant Conservation, Botany Department, University of Cape Town, Private Bag Rondebosch 7701, South Africa
2 Southern African Hotspots Programme, Conservation International, Terrestrial Ecology Research Unit, University of Port Elizabeth, PO Box 1600, Port Elizabeth 6000, South Africa
* Corresponding author, email: [email protected]
Received 25 November 2002, accepted in revised form 29 November 2002
John Acocks died in 1979 after working for nearly 50 years as a botanist in South Africa. His scientific contributions have had a profound influence on southern African ecology and this introductory article which includes a biographical sketch of his life, places his contribution in perspective. The 10 articles which appear in this issue have been prepared not only as a tribute to his contribution but also as an assessment of its current utility. Scientific thought is constantly changing and an attempt has been made to indicate where Acocks’ views are still supported by current evidence and where revision is necessary. His contribution lay in three main areas. Firstly, his description of the vegetation (or Veld Types) of South Africa remains a work of considerable importance and will probably never be repeated at the same level of scale, by a single individual, again. Three articles show that when assessed at a smaller scale his Veld Type concept is robust in some, but not all, cases. Differences between Acocks’ views and current treatments of the data are highlighted for the Bankenveld and for the vegetation of the Subtropical Thicket and Nama-karoo biomes. Acocks’ second important influence concerns his views on pre-colonial vegetation and the extent of human impact. He could not have presaged the explosion of palaeoenvironmental techniques which have arisen since his death and which have provided a somewhat different view of pre-colonial environments from the one he articulated, particularly with regard to the influence of fire on grasslands, savannas and forests. Although his views on the expansion of the eastern Karoo are not upheld in the light of recent findings there is good evidence for significant changes in the fauna and flora of the Karoo over the last 300 years. Acocks’ final contribution lay in the field of veld restoration and grazing management where he continues to have an influence on a small sector of the farming and range science community today. Not only has John Acocks provided a rich theoretical framework for scholars to test but he has also left a legacy of well-organised data for future generations. The final two papers in this special issue indicate the utility of his archives which will gain in value over the years. Challenges to Acocks’ views will continue apace and much of what he has written will undoubtedly be revised. This doesn’t detract from his contribution in any way but serves to highlight the importance of the foundation that he created during his lifetime and which we acknowledge in this special issue.
South African Journal of Botany 2003, 69:7–26
Copyright© NISC Pty Ltd, www.nisc.co.za
A reappraisal of Acocks’ Bankenveld: origin and diversity of vegetation types
GJ Bredenkamp1* and LR Brown2
1 African Vegetation and Plant Diversity Research Centre, Department of Botany, University of Pretoria, Pretoria 0002, South Africa
2 Applied Natural Sciences, Technikon SA, Private Bag X6, Florida 1710, South Africa
* Corresponding author, e-mail: [email protected]
Received 2 October 2002, accepted in revised form 15 November 2002
The great variety of vegetation types found in the Bankenveld was assessed by randomly selecting 220 relevés, representing the major vegetation types, from 23 phytosociological studies from data stored in the TURBOVEG database at the University of Pretoria. These relevés were classified by using TWINSPAN and then refining the result in MEGATAB. The phytosociological table was reduced to 120 relevés which represent 16 major vegetation types found in the Bankenveld. An assessment was made to relate the vegetation types to various phytochoria and it is concluded that the Bankenveld has definite floristic affinities to the grassland of the interior plateaux of South Africa, the savannas of the Sour Bushveld and Sourish Mixed Bushveld, the Drakensberg Afromontane vegetation and the Kalahari vegetation.
South African Journal of Botany 2003, 69: 27–51
Copyright© NISC Pty Ltd, www.nisc.co.za
Acocks’ Valley Bushveld 50 years on: new perspectives on the delimitation, characterisation and origin of subtropical thicket vegetation
JHJ Vlok1*, DIW Euston-Brown1 and RM Cowling1, 2
1 Department of Botany, Terrestrial Ecology Research Unit, University of Port Elizabeth, PO Box 1600, Port Elizabeth 6000, South Africa
2 Southern African Hotspots Programme, Conservation International, Terrestrial Ecology Research Unit, University of Port Elizabeth, PO Box 1600, Port Elizabeth 6000, South Africa
* Corresponding author, e-mail: [email protected]
Received 15 October 2002, accepted in revised form 26 November 2002
We present the approach and results of an intuitive, expert-based mapping exercise to identify subtropical thicket (including Acocks’ (1953) Valley Bushveld, Noorsveld and Spekboomveld) vegetation types as features for conservation planning. The study area comprised 105 500km2 in southern and south-eastern South Africa, the planning domain for the Subtropical Thicket Ecosystem Planning (STEP) Project. We developed a four-tier typological hierarchy based on geography, floristics, structure and grain. This yielded 112 unique thicket vegetation types, 78 of which comprised thicket clumps in a matrix of non-thicket vegetation (mosaics). By identifying mosaics, we expanded the subtropical thicket concept and increased its extent in the study area by between 1.8 and 2.8 times that of earlier assessments. We also compiled a list of plant species that yielded a rich flora of 1 558 species, 20% of which are endemic to our expanded thicket biome. Consistent with previous studies, endemics were strongly associated with succulent members of the Aizoaceae, Asphodelaceae, Euphorbiaceae, Apocynaceae and Crassulaceae. We discuss our results in terms of Acocks’ (1953) typology as well as those of more recent treatments, and comment on the evolution of subtropical thicket vegetation. Although some confusion regarding the delimitation and characterisation of thicket was resolved by this study, much more research is required to develop and test hypotheses on the determinants of thicket boundaries and the origins and evolution of thicket species.
South African Journal of Botany 2003, 69: 52–61
Copyright© NISC Pty Ltd, www.nisc.co.za
Nama-karoo veld types revisited: a numerical analysis of original Acocks’ field data
MC Rutherford1*, L Mucina2 and LW Powrie1
1 Kirstenbosch Research Centre, National Botanical Institute, Private Bag X7, Claremont 7735, South Africa
2 Department of Plant Sciences, University of the Free State, Private Bag X13, Phuthaditjhaba 9866, South Africa
* Corresponding author: [email protected]
Received 15 November 2002, accepted in revised form 28 November 2002
This paper assesses Acocks’ veld types against a reclassification of his own data for the Nama-karoo using a suite of multivariate techniques. The analysis showed that the vegetation of Nama-karoo can be partitioned into three major clusters with the most clearly defined cluster corresponding to areas in the arid north-west. Within these clusters the species groups or pools substantiated a number of Acocks’ veld types and some of their subdivisions. Notable in this regard are the veld types Orange River Broken Veld and Arid Karoo as well as some of their subdivisions. The findings suggest that some of these subdivisions could well have been raised to full veld type status. Also confirmed was the nebulous nature of Central Upper Karoo and False Arid Karoo with gradual transitions to most neighbouring veld types.
Not supported by the analysis are False Succulent Karoo and several veld types, or parts of veld types in the south-eastern Nama-karoo. Non-coincidence with the units of the numerical analysis in the latter area may also be a consequence of a mismatch between Acocks’ large sample areas and his relatively fine mapping scale in this particular region.
South African Journal of Botany 2003, 69: 62–67
Copyright© NISC Pty Ltd, www.nisc.co.za
John Acocks and the expanding Karoo hypothesis
ME Meadows
Department of Environmental and Geographical Science, University of Cape Town, Rondebosch 7701, South Africa
e-mail: [email protected]
Received 8 June 2002, accepted in revised form 17 September 2002
John Acocks’ ideas on the recent and future changes of vegetation in South Africa occupy an important conceptual position in the first and subsequent editions of Veld Types of South Africa. Arguably the most prominent idea embodied in his discussion of vegetation changes is the hypothesis that various Karoo veld types were expanding eastwards and northwards into areas that would otherwise be occupied by grassland, and that this process was a direct result of mismanagement of the semi-arid rangelands. The invasion of Karoo vegetation amounts to a systematic consideration in South Africa of what would ultimately become known as desertification. This paper examines Acocks’ interpretation of the vegetation changes associated with expanding Karoo and desert veld types and his evidence that this was indeed occurring. It places the apparent degradation into an appropriate historical context in relation to the evolving views of other South African and international scientists. The paper shows how Acocks’ understanding of vegetation dynamics influenced agricultural policy, both immediately following publication of Veld Types and subsequently. Finally, a critique of the spreading Karoo hypothesis is developed in relation to current theory on desertification and its implications for management of the semi-arid rangelands of South Africa today.
South African Journal of Botany 2003, 69: 68–78
Copyright© NISC Pty Ltd, www.nisc.co.za
Did the flora match the fauna? Acocks and historical changes in Karoo biota
WRJ Dean* and SJ Milton
Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch 7701, South Africa
* Corresponding author, e-mail: [email protected]
Received 8 June 2002, accepted in revised form 17 September 2002
Years of observation in Karoo veld convinced JP Acocks that the perennial grasses that he occasionally encountered in barren Karoo landscapes were remnants of pre-colonial vegetation. He maintained that desertification, caused by overgrazing and alteration of drainage systems, had destroyed key grazing resources, reducing the carrying capacity of the vegetation for large herbivores. We attempt to test this notion by reconstructing the fauna for sample areas of the Karoo from farm names, plant common names and travellers records, and by examining the flora of these areas for evidence of co-evolution with large herbivores. We concluded that names of mapped features and farms that refer to animals do reflect the historical distribution of these animals. However, within Karoo sampling units of approximately 500km2, we could find no close relationship between historical records of large herbivores and herbivore-adapted defence and dispersal traits of plants. This weak evidence for co-evolution might have been because many of the large herbivores were not permanent residents in the Karoo. Alternatively it might be an artefact caused by lack of abundance data for plant guilds. There is evidence that post-colonial land use of the Karoo has changed vegetation structure and productivity within the areas we sampled.
South African Journal of Botany 2003, 69: 79–91
Copyright© NISC Pty Ltd, www.nisc.co.za
What controls South African vegetation — climate or fire?
WJ Bond1*, GF Midgley2 and FI Woodward3
1 Botany Department, University of Cape Town, Private Bag Rondebosch 7701, South Africa
2 Climate Change Research Group, National Botanical Institute, P/Bag X7, Claremont 7735, South Africa and Conservation International, Center for Applied Biodiversity Science, 1919 M St, NW, Washington DC 20036, USA
3 Department Animal and Plant Sciences, University of Sheffield, Sheffield, UK
* Corresponding author, e-mail: [email protected]
Received 21 June 2002, accepted in revised form 2 October 2002
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.
‘Temperature
and moisture are the two master limiting factors in the distribution of life on
Earth’
Krebs
(2001)
South African Journal of Botany 2003, 69: 92–98
Copyright© NISC Pty Ltd, www.nisc.co.za
‘Nature’s method of grazing’: Non-Selective Grazing (NSG) as a means of veld reclamation in South Africa
MT Hoffman
Institute for Plant Conservation, Botany Department, University of Cape Town, Private Bag Rondebosch 7701, South Africa
e-mail: [email protected]
Received 17 September 2002, accepted in revised form 13 November 2002
Acocks was concerned with the past, present and future state of South Africa’s vegetation and in the 1960’s, together with several farmers in the eastern Karoo, developed a grazing system which he thought would restore the vegetation to its former pristine condition. Acocks felt that the grazing systems advocated by the Department of Agriculture at the time were partly responsible for the degraded vegetation of the region as these systems encouraged livestock to graze selectively, thereby overgrazing the more palatable species in the vegetation. He felt that by forcing animals to graze all species non-selectively, the more palatable elements would be able to out-compete the less palatable species and dominate the vegetation as he believed they once did in pre-colonial times. Acocks found theoretical support for his argument which also relied on relatively long rest periods between grazing events and suggested that this non-selective grazing system simulated the way in which the pre-colonial ungulate herds utilised the vegetation. Although Acocks never conducted the key experiments needed to test his ideas, his approach was supported by several farmers in the eastern Karoo who conducted trials on their farms to test the principles of the method. The approach advocated by Acocks, however, was in direct contrast to that proposed by the Department of Agriculture who were concerned about the comparatively high stocking rates advocated under Acocks’ Non-Selective Grazing (NSG) system. Their own experiment on NSG found that it reduced plant cover and increased erosion and they believed that it would lead to further widespread degradation if implemented. Although Acocks was employed by the Department of Agriculture as a Botanical Survey Officer he was not a Pasture Research Officer and it was this latter group of employees who had the responsibility of researching and advocating appropriate grazing systems for South Africa’s rangelands. Acocks was, therefore, instructed not to promote NSG in his official capacity. Despite this, Acocks’ writing in the last ten years of his life is infused with the ideas of NSG which continue to influence the development of range management systems to the present.
South African Journal of Botany 2003, 69: 99–104
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ACKDAT: a digital spatial database of distributions of South African plant species and species assemblages
MC Rutherford*, LW Powrie and GF Midgley
Kirstenbosch Research Centre, National Botanical Institute, Private Bag X7, Claremont 7735, South Africa
* Corresponding author, e-mail: [email protected]
Received 12 November 2002, accepted in revised form 20 November 2002
The fieldwork that underpins John Acocks’ work on the Veld Types of South Africa, was recorded in a set of field notebooks, which were preserved after Acocks’ retirement. These are adequately geo-referenced to allow the construction of a relational database linking more than 7 000 species’ presence, abundance and site location data at more than 3 000 sites throughout much of South Africa. The database is described with reference to data quality, representivity and spatial precision. Some appropriate and inappropriate types of uses of the data are illustrated.
South African Journal of Botany 2003, 69: 105–115
Copyright© NISC Pty Ltd, www.nisc.co.za
Change in land use and botanical composition of KwaZulu-Natal’s grasslands over the past fifty years: Acocks’ sites revisited
TG O’Connor1*, CD Morris2 and DJ Marriott1
1 Range and Forage Resources, University of Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
2 Range and Forage Institute, Agricultural Research Council, c/o Range and Forage Resources, University of Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
* Corresponding author, e-mail: [email protected], address: PO Box 379, Hilton 3245, South Africa
Received 10 January 2002, accepted in revised form 1 April 2002
Acocks measured representative sites of good condition grassland in the 1940’s that were re-sampled approximately 50 years later in order to compare the effect of commercial versus communal grazing on compositional change. Most of the Mistbelt ‘nGongoni Veld had been afforested, a third of Highland Sourveld or Northern Tall Grassveld had been transformed by cultivation or afforestation, while most of Southern Tall Grassveld had remained as grassland. For untransformed sites sampled in 1996, the composition of communally and commercially grazed land differed distinctly, although differences depended on an altitudinal gradient reflecting water availability. Sites under communal grazing supported a higher proportion of short-lived, perennial grass species, often of poor grazing value. From measurement of the extent of compositional change of each site, commercially grazed sites showed no consistent pattern of change, and the average extent of change was small. By contrast, communally grazed sites had on average changed considerably, although the direction of change had depended on the physical environment. Basal cover increased with altitude, with that of commercial rangeland consistently 5% higher than that of communal rangeland. Notwithstanding sampling problems of accurate relocation of his plots and adequately matching his subjective method of data collection, Acocks’ data has provided an invaluable opportunity for examining vegetation change over an appropriate time scale for vegetation comprised of perennial plants.