Succulent Thicket Research Articles

The rediscovery of Ornithogalum britteniae (Hyacinthaceae) and an amendment to the description

Ornithogalum britteniae F.M. Leight. ex Oberm., described in 1978 and until now only known from the type specimen of uncertain origin, was recollected near Grahamstown in 2001 enabling the description and illustration of leaf surface, pollen, capsule, seed and habitat for the first time. The conservation status is assessed following the current IUCN red data criteria and a status of Vulnerable (VU A3cD2) is applied. The habitat, an ecotone between Succulent Thicket and Nama-Karoo, is discussed in light of the high succulent plant diversity and several rare and localised endemic species found there.

Comparing biodiversity between protected areas and adjacent rangeland in xeric succulent thicket, South Africa: arthropods and reptiles

Summary 1. Although it is widely assumed that protected areas conserve species that would not survive elsewhere, this assumption is seldom tested. The aim of the study was to determine the respective roles of a nature reserve and commercial and subsistence rangeland in preserving terrestrial arthropods and reptiles in xeric succulent thicket in the Eastern Cape, South Africa. 2. Faunal diversity on a nature reserve (the Great Fish River Reserve Complex) was compared with a historically overgrazed commercial farm, an intensively managed, conservatively stocked commercial farm and a communal grazing area. Terrestrial arthropods and reptiles were caught in paired pitfall traps inside and outside the nature reserve, specimens being sorted into recognizable taxonomic units (RTU). The taxa occurring in each land management unit were compared using RTU diversity, a hierarchical richness index (HRI), community similarity and uniqueness. 3. The nature reserve contained more RTU and a greater HRI than adjacent land for most arthropod groups, and also supported more unique taxa than the other study localities. 4. Snakes and lizards, in contrast, were almost twice as abundant in the communal grazing area as elsewhere, although reptile species diversity was similar at all localities. 5. Each individual locality contained fewer than 62% of the total number of arthropod RTU and 55% of the total reptile RTU; the communal grazing area contained only 37% of the total number of arthropod RTU collected in the study area. 6. Nineteen (73%) of the ant, 18 (69%) of the weevil, 60 (70%) of the spider and 12 (60%) of the grasshopper RTU and 10 (66%) of the reptiles were shared by the three land uses. Six new weevil species and probably several new arachnid species were collected, but all the new weevils were confined to the nature reserve. 7. The communal grazing area differed most from the nature reserve in richness and community composition, followed by the conservatively stocked commercial farm. The historically overgrazed commercial farm was most similar to the nature reserve. 8. The communal grazing area was characterized by xeric‐adapted reptiles and predatory arthropods whose ranges are centred in the semi‐arid parts of South Africa. In contrast, the nature reserve and commercial farms supported more mesic‐adapted reptiles and herbivorous arthropods. 9. Synthesis and applications. The data show how protected areas are key to conserving those species that decrease under heavily grazed and disturbed conditions. However, they also illustrate that diverse land‐use mosaics promote gamma diversity in the xeric succulent thicket of South Africa. Conservation policies that include protected space in the wider environment and conserve habitat diversity are likely to both promote regional richness and support scarce species.

Predicting the extent of succulent thicket under current and future climate scenarios

Using data from the distribution records of the facultative CAM succulent shrub Portulacaria afra, and high resolution climate response surfaces, we developed a spatially explicit model of the potential distribution of the species in the Thicket Biome of the eastern and southern Cape, South Africa. The resultant map shows a close relationship with the expected distribution of P. afra prior to the advent of intensive ranching by goats in the region. In field situations where P. afra is known to have been cleared by agricultural activities, the map showed the potential of the site for this species. It also demonstrated the absence of the species in areas where it does not occur e.g. fynbos, grasslands, forest and Nama-karoo. A weakness of the model is the lack of a measure of the density of P. afra. Under the CSM (coupled ocean-atmosphere model) climatic change scenario, 80.3% of the grid-cells would remain suitable and 19.7% would become unsuitable.

Landscape diversity in a conservation area and commercial and communal rangeland in Xeric Succulent Thicket, South Africa

Nature reserves in Xeric Succulent Thicket of South Africa contain a greater diversityof wildlife and correspondingly a greater diversity of disturbance agents thanadjacent, unconserved freehold and communal rangeland. Although more lightlystocked, it is unknown whether protected areas contain a higher diversity oflandscape patches (i.e., sub-landscape features such as bush clumps,termitariums, bare patches or animal wallows) which could influence thereflectance value of a single pixel depicting a 20 × 20 marea in a SPOT satellite image, than unconserved land. Our key questions were:How does patch diversity in a nature reserve compare with that on commercial andcommunal rangeland? Can pixel diversity in a SPOT satellite image be used toquantify these differences? And, is there a correlation between reflectancediversity in a SPOT image and patch diversity on the ground? As a first step,the coefficients of variation (CV) for 10 groups of 12 picture-element (pixel)values of a dry season SPOT satellite image were calculated for two commercialfarms and a communal rangeland. The same data were collected on a naturereserve, 50 to 100 m inside the boundary between the reserve andthe freehold or communal rangeland. Next, we recorded the variety of 20 ×20 m plots on the ground, also in groups of 12 plots, at the samegeographical coordinates as the satellite-based measurements. The means of thesatellite-based and ground-based indeces were significantly and positivelycorrelated. In addition, the nature reserve displayed significantly higher pixelCVs than the communal rangeland, and also contained significantly higherground-based diversity indeces than the freehold, and possibly the communal,rangeland. We postulate that the higher landscape patchiness in the naturereserve is a result of the diversity of disturbances caused by wildlife(especially megaherbivores) coupled with naturally low stocking rates, while thelower diversity in the communally managed rangeland is the result of continuousheavy grazing coupled with intensive fuelwood harvesting. The satellite-basedtechnique is useful for identifying potential sites of high biodiversity,wherein more intensive sampling at a finer scale can be undertaken. It is,however, important to use dry season imagery because of the temporary‘masking’ effect of ephemerals during the wet season.

Protecting plants from elephants: botanical reserve scenarios within the Addo Elephant National Park, South Africa

At current densities, elephants are having a severe impact on plant community structure and species richness in the Addo Elephant National Park (AENP), Eastern Cape, South Africa. Those species that are particularly vulnerable to elephants comprise the bulk of the regionally endemic, Red Data Book and rare species (special species) associated with succulent thicket, a vegetation type endemic to the Eastern Cape. The AENP is the only national park in South Africa that contains succulent thicket. Other thicket-containing reserves exist but have insufficient management resources. The AENP can be divided into 16 units based on management and grazing history. Using these units, we show a strong relationship between the duration of exposure to elephant impacts and the richness and density of special species in the Park. Using an iterative reserve-selection procedure, we identify a core system of five botanical reserves within the Park. This system would represent 91% of the Park's special plant species in less than 8% of its area. We recommend an implementation strategy based on the irreplaceability and vulnerability values of each unit, and each species. This involves the maintenance of three existing botanical reserves, the establishment of two additional reserves, the deproclamation of one existing reserve, and further conservation actions to ensure the protection of those special species not included within the core system of botanical reserves. We also provide suggestions for the resolution of the conflicts between elephant conservation and maintenance of plant biodiversity in the AENP.

The flora of the Addo Elephant National Park, South Africa: are threatened species vulnerable to elephant damage?

The Addo Elephant National Park in the warm-temperate Eastern Cape was proclaimed in 1931 to protect one of the four elephant populations in South Africa which survived into the present century. However, since the late 1970s, a major objective of the Park is to protect intact a viable example of succulent thicket – the regional ecosystem. Succulent thicket is endemic to the Eastern Cape and forms the major component of the Albany Centre, a floristic region of high diversity and endemism, especially among succulent shrubs and geophytes. This ecosystem is poorly represented in the reserve system and is highly threatened by overgrazing and clearing for agriculture. Under the present stocking rate of more than two elephants/km2, succulent thicket in the Park has been severely impacted: in particular, biomass, stature and plant diversity have been reduced. We show that the flora of the Park is of great regional significance. Of a total of 581 species, 12.4% were classified as regional endemics and/or Red Data Book species (collectively termed 'species’ of special concern), and 32.2% were not known to be conserved in any other succulent thicket protected area. Relative to the remainder of the flora, both categories of species were over-represented among succulent shrubs (predominantly Euphorbiaceae and Mesembryanthemaceae) and geophytes (predominantly Asphodelaceae and Hyacinthaceae). This taxonomic and biological profile coincides with that of species vulnerable to local extinction as a result of elephant impacts. The Park authorities will need to find a solution to the conflict between maintaining a large population of megaherbivores, and maintaining the structure and diversity of succulent thicket.

Changes to the vegetation of the mid‐Fish River valley, Eastern Cape, South Africa, in response to land‐use, as revealed by a direct gradient analysis

Degradation of natural rangeland is a serious problem throughout southern Africa. It has been suggested that incorrect grazing management practices have resulted in a decrease in the production potential of rangelands. In order to explore the nature and extent of degradation at the landscape scale, we selected a study site where a range of land‐use and rangeland management practices could be studied in parallel. The mid‐Fish River valley consists of three markedly different units of land management, namely, commercial rangelands, communal rangelands and nature conservation areas. Using a direct gradient analysis approach, the vegetation of the study area was classified into homogenous units. A shift in the vegetation composition in response to different land‐use treatments was investigated. The results of the classification showed three major plant communities present in the study area, namely, Short Succulent Thicket, Medium Succulent Thicket and Mesic Bushclump Savanna. The results revealed a definite grazing gradient within the study area. It showed that an increase in grazing intensity resulted in a transformation from vegetation synonymous to a mesic environment towards that found in an arid environment. As grazing pressure increased there was a decrease in palatable grasses, succulents and herbaceous species and an increase in dwarf karroid shrubs.

The impact of elephant and goat grazing on the endemic flora of South African succulent thicket

Succulent thicket is an important centre of endemism for succulents and geophytes. Both inside and outside reserves, this component is threatened by megahervibore and goat grazing, respectively. Goat grazing has greatly reduced the cover and diversity of endemic geophytes and succulent shrubs in succulent thicket has in the Addo Elephant National Park. Elephant grazing has had a more moderate effect on these plants and has not reduced the rich Crassulaceae flora in shrub microsites. All endemics noted in the study were present in ungrazed sites but fewer were recorded in the elephant- (63%) and goat- (53%) grazed treatments. There are several solutions to this problem: more botanical (ungrazed) reserves should be established; reserves should be enlarged to reduce the stocking density of elephants; and elephant and other game farming should be encouraged as an alternative to goat-farming outside reserves.

Effects of elephants and goats on the Kaffrarian succulent thicket of the eastern Cape, South Africa: G. C. Stuart-Hill, Journal of Applied Ecology, 29(3), 1992, pp 699–710

Effects of elephants and goats on the Kaffrarian succulent thicket of the eastern Cape, South Africa: G. C. Stuart-Hill, Journal of Applied Ecology, 29(3), 1992, pp 699–710

Effects of Elephants and Goats on the Kaffrarian Succulent Thicket of the Eastern Cape, South Africa

1. Kaffrarian succulent thicket is a dense, semi-succulent, thorny vegetation which is rapidly being eliminated under current pastoral systems. To understand why this occurs, the effect of defoliation by wild herbivores (mostly elephant) was compared with that of domestic ungulates (mostly goats) from surveys inside and outside the Addo Elephant National Park. 2. Both elephants and goats reduced canopy cover and increased shrub density in relation to control areas. Goats reduced the number of dominant shrub species per quadrat. 3. Replacing elephants with goats resulted in a fundamental change in the shrub community to one dominated by small, unpalatable shrubs with a few scattered umbrella-shaped trees

A syntaxonomic and synecological account of the vegetation of the eastern Cape midlands

An hierarchical syntaxonomic classification of the vegetation of the eastern Cape midlands is presented as a second approximation after the earlier work by Acocks (1988). Detail on geomorphology, geology, climate and early vegetation history is provided. The study area was stratified from Landsat MSS imagery and the community classification generated using two-way indicator species analysis (Twinspan). Tabular comparisons and final sorting of tables are according to the methods and techniques of the Zurich–Montpellier school of phytosociology. Syntaxonomic ranks are defined as five classes, nine orders and 17 communities. Classes are Grasslands (two orders, three communities), Karoo Shrublands (one order, five communities), Karoo Dwarf Shrublands (four orders, five communities) and Sub-tropical Transitional Thicket (one order, three communities), with one community representing the Riparian Thicket. In addition to diagnostic floristic elements, syntaxa are further characterized using structural and habitat criteria. The distribution of the syntaxa corresponds with the precipitation gradient experienced in the study area. Succulent Dwarf Shrublands occur in areas of low mean annual precipitation ( 450 mm per annum. Succulent Thicket occupies warm, dry sites on rocky, sloping landforms.

Plant communities of the Riversdale Plain

The vegetation of the Riversdale coastal plain was classified and described using Campbell’s (1985) approach. Data collected included a subset of Campbell’s structural and higher taxon characters, as well as dominant (> 10% cover) species, which would enable the recognition of communities to at least the subseries level in his hierarchy. The classification was produced using the Braun-Blanquet method of table sorting. Twenty zonal communities, at various hierarchical levels, were recognized and mapped. Non-fynbos communities included Afromontane Forest, Eastern Forest and Thicket, Kaffrarian Succulent Thicket and Dune Thicket Series in the Forest and Thicket Group, and Renoster Shrubland. Fynbos communities were Mesotrophic Grassy Fynbos, three subseries of Asteraceous Fynbos (Mesotrophic, Dune and Oligotrophic), Azonal Restioid Fynbos, Wet Proteoid Fynbos, Dry Proteoid Fynbos and six types of Mesic Proteoid Fynbos. The vegetation types could all be integrated into Campbell’s Fynbos Biome mountain vegetation concepts and modifications based on work on the Agulhas plain. The mapped communities are adequate for conservation planning and comprise an essential descriptive basis for future studies. The data on Proteaceae cover corresponds well to that of the Restionaceae for Proteoid Fynbos — together the two families comprise the only groups which could be used for a classification without requiring extensive floristic studies. Die plantegroei van die Riversdale seevlakte word geklassifiseer en beskryf deur gebruik te maak van Campbell (1985) se benadering. Die data wat versamel is, bevat ’n subgroup van Campbell se strukturele en hoër takson-karakters, sowel as dominante (> 10% bedekking) spesies, wat die uitkenning van gemeenskappe tot op die subserievlak in sy hierargie moontlik maak. Die klassifikasie is teweeg gebring deur gebruik te maak van die Braun-Blanquet metode van tabel-sortering. Twintig streeksgemeenskappe is op verskeie hierargiese vlakke geïdentifiseer en gekarteer. Nie-fynbos-gemeenskappe het die volgende ingesluit: Afromontane Woude, Oostelike Woud en Ruigte, Kaffrariese Sukkulente Ruigte en Duine Ruigte Series, in die Woud en Ruigte Groep, en Renosterstruikveld. Fynbos-gemeenskappe het Mesotrofiese Grasagtige Fynbos, drie subseries van Komposiet-Fynbos (Mesotrofiese, Duine en Oligotrofiese), Azonal Restioïede-Fynbos, Nat Proteoïede-Fynbos, Droog Proteoïede-Fynbos en ses tipes van Mesiese-Proteoïede-Fynbos ingesluit. Die gemeenskappe kan almal met Campbell se Fynbos-Bioom-plantegroeikonsepteen modifikasies daarop, gebaseer op werk in die Agulhasvlakte, geïntegreer word. Die gekarteerde gemeenskappe is voldoende vir die beplanning van bewaringsaksies en behels ’n essensiële beskrywende basis vir toekomstige studies. Die data oor Proteaceae-bedekking vergelyk goed met die van die Restionaceae in Proteoïede-Fynbos— gesamentlik is die twee families die enigste groepe wat vir ’n klassifikasie gebruik word sonder om verdere floristiese studies uit te voer.

The vegetation of the Karoo Nature Reserve, Cape Province. I. A phytosociological reconnaissance

A phytosociological survey according to the approach and methods of the Zürich–Montpeillier school was carried out on the Karoo Nature Reserve, Graaff-Reinet, South Africa. The study area is 160 km 2 in extent, and climatically it falls within the semi-arid zone. The complex climatological, geological, soil, vegetation and land-use gradients are emphasized. Eleven natural plant communities are recognized, reflecting a gradient from the warm, xeric conditions of the pediments to the cool, mesic conditions of the mountain ridges and plateaux. An hierarchical classification of the communities has been prepared, with the first division, corresponding roughly to the level of order, dividing the vegetation into Shrubland, Succulent Thicket and Dwarf Shrubland. The Shrubland is further divided into Open Shrubland on rocky slopes, Open Shrubland on dolerite upland and Grassy Open Shrubland. The Dwarf Shrubland is divided into grassy, succulent and degraded forms. ’n Fitososiologiese opname, waarin gebruik gemaak is van die benadering en metodiek van die Zürich–Montpellier-skool, is uitgevoer in die Karoo-Natuurreservaat, Graaff-Reinet, Suid-Afrika. Die klimaat is semi-aried en die studiegebied is 160 km 2 in oppervlakte. Die komplekse gradiente in klimaat, geologiese struktuur, gronde, plantegroei en bodembenutting word beklemtoon. Elf natuurlike plantgemeenskappe, wat die gradiënt van die warm, droë toestande van die vlaktes na die koel, klam toestande van die bergrante en plato’s, word beskryf. ’n Hiërargiese klassifikasie van die gemeenskappe is voorberei. Die eerste skeiding, wat min of meer met die vlak van orde ooreenstem, het die plantegroei in Struikveld, Sukkulente Bosveld en Dwergstruikveld ingedeel. Die Struikveld is verder in Ope Struikveld van die klipperige Randjies, Ope Struikveld van die Doleriet-hoogland en Grasagtige Ope Struikveld onderverdeel. Die Dwergstruikveld is in grasagtige, sukkulente en versteurde vorms ingedeel.

A classification of the subtropical transitional thicket in the eastern Cape, based on syntaxonomic and structural attributes

Subtropical transitional thicket, traditionally known as valley bushveld, covers a significant proportion of the eastern Cape. This paper attempts to classify the subtropical transitional thicket into syntaxonomic and structural units and relate it to other thicket types on a continental basis. Twelve sites along a rainfall gradient were sampled for floristic and structural attributes. The floristic data were classified using TWINSPAN. Results indicate that the class subtropical transitional thicket has at least two orders of vegetation, namely kaffrarian thicket and kaffrarian succulent thicket. Two forms of thicket were recognized for both these orders viz. mesic kaffrarian thicket and xeric kaffrarian thicket for the kaffrarian thicket and mesic succulent thicket and xeric succulent thicket for the kaffrarian succulent thicket. Ordination of site data by DECORANA grouped sites according to these vegetation categories and in a sequence along axis 1 to which the rainfall gradient can be clearly related. Variation within the mesic kaffrarian thicket was however greater than between some of the other thicket types, indicating that more data are required before these forms of thicket can be formalized. Composition, endemism, diversity and the environmental controls on the distribution of the thicket types are discussed. ’n Aansienlike gedeelte van die Oos-Kaap word beslaan deur subtropiese oorgangsruigte, wat tradisioneel as valleibosveld bekend is. Hierdie studie is ’n poging om subtropiese oorgangsruigte in sintaksonomiese en strukturele eenhede te klassifiseer en dit op ’n kontinentale basis in verband met ander ruigtetipes te bring. Opnames vir floristiese en strukturele eienskappe is op twaalf persele langs ’n reënval-gradient gedoen. Die floristiese gegewens was met behulp van TWINSPAN geklassifiseer. Resultate dui aan dat die klas subtropiese oorgangsruigte uit ten minstens twee ordes plantegroei, naamlik kaffrariese ruigte en kaffrariese sukkulenteruigte bestaan. Twee soorte ruigte was vir elke van die twee ordes herken. Die kaffrariese ruigte bestaan uit mesiese kaffrariese ruigte en xeriese kaffrariese ruigte, terwyl die kaffrariese sukkulenteruigte uit mesiese sukkulenteruigte en xeriese sukkulenteruigte bestaan. Ordening van data deur DECORANA het die persele van hierdie plantegroeitipes in ’n gradient langs as 1 gerangskik. Die reënvalgradient word langs hierdie gradient verteenwoordig. Variasie binne die mesiese kaffrariese ruigte was groter as tussen sommige van die ander ruigtetipes wat aantoon dat meer gegewens hier benodig word voordat hierdie tipes ruigte geformaliseer kan word. Samestelling, endemisme, diversiteit en die invloed van die omgewing op die verspreiding van die ruigtetipes is bespreek.

Phytochorology and Vegetation History in the South-Eastern Cape, South Africa

Using the results of a descriptive and an historical approach, hypotheses are presented on vegetation history during a glacial-interglacial sequence in the chorologically complex south-eastern Cape. In the descriptive approach 879 taxa from fynbos, renosterveld, subtropical thicket and Afromontane forest communities are classified into phytochorological groups according to their distribution relative to major African phytochoria. The relative occurrence of these phytochorological groups in the different communities are determined. Taxa typical of the Cape phytochorion predominated in fynbos communities, particularly in Mountain Fynbos; there was a strong CapeAfromontane linking element in Grassy Fynbos and Cape-Tongaland-Pondoland linking element in Dune Fynbos. Phytochorological spectra of renosterveld communities were complex and dominated by Cape linking elements. Afromontane endemics predominated in Afromontane forests while the spectra of subtropical thicket communities were dominated by taxa characteristic of the Tongaland-Pondoland Region. In mesic thicket there was a strong Afromontane component whereas karroid taxa were conspicuous in the drier succulent thicket. Levels of endemism were highest for Cape taxa in fynbos, and succulent karroid taxa in dry thicket. Very few subtropical and Afromontane endemics were recorded. In an historical approach, the palaeoenvironment of the Cape coastal region during the last glacial maximum to Holocene sequence is discussed briefly as a model for predicting vegetation change. Available data on phylogeny, speciation and endemism of taxa characteristic of S.E. Cape phytochoria are discussed in their historical perspective. From a consideration of the descriptive and historical components of the study the following hypotheses on vegetation history are generated. Cape fynbos has had a long history in the S.E. Cape and elsewhere in the Cape Region. Its distribution on edaphic 'islands' associated with infertile soils derived from quartzites and sandstones of the mountains would not have been disrupted to any extent, during a glacial-interglacial cycle. Renosterveld is a chorologically complex vegetation type whose distribution on the moderately fertile soils in the Cape Region would have fluctuated dramatically depending on prevailing climatic conditions. Subtropical thicket and grassland and Afromontane forest would have been largely displaced from the Cape Region during the last glacial and would have only become established on certain edaphic sites in the area, with the onset of a warmer, wetter Holocene climate. Karroid taxa have had a lengthy history in the S.L. Cape and during drier glacial times karroid communities would have occupied much of the terrain presently supporting renosterveld and thicket. *Present address: School of Biology, Western Australian Institute of Technology, Bentley 6102, Western Australia.