No previous scientific surveys have been conducted on inselbergs in the Drakensberg. The aim of this study was to collect specimens, identify, describe and name the vegetation clusters and assess biogeographical connections with other Afromontane regions. A total of 103 relevés where sampled from six inselbergs. The plant sampling was carried out according to the Braun-Blanquet method with the plant and environmental data entered in TURBOVEG and exported as a Cornell Condensed format file (CC!) into Juice. Classification was completed using TWINSPAN (Two-way Indicator Species Analysis) (modified), resulting in 4 major communities, 11 communities, 13 sub-communities and 18 variants. Ordination (indirect) was carried out using CANOCO (version 4.5) to investigate the relationship between species. The four major communities identified are
Studies of high-altitude inselbergs within the east and southern Afromontane region are few. Whilst studies of inselbergs in Africa have been concentrated more in West Africa (Barthlott, Gröger & Porembski
This article is the first phytosociological survey of the high-altitude inselbergs in the Drakensberg. Its aims are to (1) classify the inselberg alpine vegetation into communities and present the species composition, (2) examine environmental gradients to identify habitats and (3) identify and examine biogeographical affinities with previously described or identified plant communities. This new knowledge will contribute to the understanding and conservation management of high-altitude alpine vegetation and species unique to the Drakensberg.
The study sites are located in the Drakensberg, South Africa, and consist of six inselbergs, all over 3000 m in altitude (
Maps of study sites: (a) study area with KwaZulu-Natal uKhahlamba-Drakensberg Park (shaded) and (b) South Africa indicating Drakensberg Alpine Centre.
Photographs of inselberg vegetation in the Drakensberg: (a) typical inselberg vegetation of low, cushion-forming fynbos shrubs and bunch grass on Outer Buttress, with the sloping peak of Sentinel in the background, (b) the flat top of Inner Buttress showing three of the four habitats: sheet rock outcrops/gravel plains, alpine grasslands and deep soil, Helichrysum/Erica fynbos grassland. Devils tooth in the foreground, (c) tall, montane grass community:
Uncommon vernal pools on Cathkin and Outer Buttress, habitat for specialist aquatic plants
A total of 103 plots where sampled on the six inselbergs. Plot sizes varied according to substrate, and were subjectively estimated at either 3 m x 3 m for sheet rock, seeps or gravel plains, or 6 m x 5 m for grass or dwarf shrub vegetation as per theoretical criteria (Westhoff & Van der Maarel
A first approximation at clustering was carried out using the TWINSPAN (Two-way Indicator Species Analysis) algorithm of Hill (
Within Juice the lower threshold values for the diagnostic, constant and dominant species when applying the ‘Analysis of columns of syntaxonomic tables’ (Tichý & Holt
The naming of plant communities was carried out according to guidelines suggested by Brown
The skewness and kurtosis calculations performed with PC-ORD version 5.0 revealed the non-unimodal distribution of the species data (also confirmed by the disjunct nature of the dataset as indicated by the DCA eigenvalue of one for the first axis) (Gauch
A final manipulation of relevé columns and species rows was carried out in Juice to fine-tune the phytosociological table, which was exported into Excel and refined for presentation by moving rows containing species and adding alphabetic letters to denote species groups (Online Appendix 1). Groups of similar ecological characteristics were identified and related to environmental gradients. The relationship of the identified plant communities with the environmental variables is presented in
Correspondence analysis of all relevés showing major communities 1, 2, 3 and 4.
Correspondence analysis with wetlands (Group 1) removed to show more clearly the gradients typifying Groups 2, 3 and 4.
A total of 103 relevés and 189 species where incorporated in the classification; 2.6% of these were Pteridophytes, 31% were Monocotyledons and 66% were Dicotyledons. There are 79 species that occur in ≥ 4 relevés and which do not form appreciable clusters, and have been left out of the formal phytosociological description. However, all species are included in Online Appendix 1. The average number of species per plot is 14.16 (s.d. 6.56), minimum 4, maximum 32. There are seven sub-communities and variants with the same numbers of relevés, diagnostic, constant and dominant species. Accordingly, only the sub-communities have been described and named whilst ignoring the variants. There are 18 variants which have different diagnostic, constant and dominant species, which have been named. Subsequently, there are 13 unique sub-communities, 18 variants, 11 communities and four major communities which form the syntaxonomical classification presented in Online Appendix 1.
TWINSPAN produced four major communities representative of four different habitats (
Major community 1: Wetland grass and forblands.
Major community 2: Sheet rock grass and forblands.
Major community 3: High-altitude alpine grassland.
Major community 4: High-altitude alpine fynbos grassland.
In
The results from
All clusters are named in the Discussion and fully listed in the Online Appendix 1.
Major community 1,
Major community 2,
Sub-community 2.1.1,
Sub-community 2.1.2,
Sub-community 2.1.3,
Sub-community 2.2.1,
Major community 3 has three communities, two sub-communities and no variants. It is named the
Major community 4,
The following three communities comprise major community 4: community 4.1,
Community 4.1,
Community 4.2,
The last community to the right on the syntaxonomic table (Online Appendix 1), community 4.3,
Some plants were found to be present throughout many of the relevés in major community 4, but with limited cover/abundance. They include six forbs, namely
The results from the phytosociological analysis indicate the inselberg vegetation has four major communities, 11 communities, 13 sub-communities and 18 variants (Online Appendix 1). Overlap exists with sub-communities and variants. The name designated for each cluster is for the highest order unit, whilst ignoring those of lower rank (Online Appendix 1). The names are:
Community 1.1,
Community 1.2,
Community 1.3,
Community 2.1,
Sub-community 2.1.1,
Variant 2.1.1.1
Variant 2.1.1.2
Variant 2.1.1.3
Sub-community 2.1.2,
Variant 2.1.2.1
Variant 2.1.2.2
Sub-community 2.1.3,
Variant 2.1.3.1
Variant 2.1.3.2
Variant 2.1.3.3
Community 2.2,
Sub-community 2.2.1,
Sub-community 2.2.2,
Community 3.1,
Community 3.2,
Sub-community 3.2.1,
Sub-community 3.2.2,
Community 3.3,
Community 4.1,
Sub-community 4.1.1,
Variant 4.1.1.1
Variant 4.1.1.2
Sub-community 4.1.2,
Community 4.2,
Sub-community 4.2.1,
Variant 4.2.1.1
Variant 4.2.1.2
Variant 4.2.1.3
Sub-community 4.2.2,
Variant 4.2.2.1
Variant 4.2.2.2
Variant 4.2.2.3
Variant 4.2.2.4
Variant 4.2.2.5
Community 4.3,
Sub-community 4.3.1,
Sub-community 4.3.2,
Major community 1 only has a single diagnostic species,
The wetland vegetation consists of 11 relevés with nine species of which only
Major community 2,
Major community 3,
Major community 4,
All inselberg vegetation has a grass component, including most of the wetlands, rocky outcrops and gravel seeps, with 89 out of 103 relevés complying. Alpine grasses provide 98% cover/abundance and consistency throughout all four major communities, with the high-altitude vegetation dominated by C3 grasses. There are two C4 grasses:
Plant physiological adaptation to alpine conditions can be seen in the large tufted grasses
The high-altitude wetland community dominated by sedges and described by Hill (
Of all regions in the Drakensberg, the inselbergs may be regarded as showing no anthropogenic influence from grazing, ploughing or fire, which does occur but is lighting induced. There is limited human presence: climbers have built cairns on most of the peaks, there are log books on Sentinel and Cathkin Peak, a bovine skull – probably a cow placed as vulture food – and the metal top of a smoke grenade was found on Cathkin, and tourists visit Inner and Outer Horn via helicopter; however, human impact is negligible, unlike the heavily impacted, overgrazed, hoof-eroded adjacent escarpment in Lesotho.
Despite the broad treatment of the southern Africa vegetation by Mucina and Rutherford (
This article does not attempt to place the plant communities into a formal syntaxonomical classification of the established hierarchy of nomenclature and existing abstract categorisations of the European Zurich-Montpellier system (Mueller-Dombois & Ellenberg
Papers on inselbergs in the Free State (Brand
Rising carbon dioxide levels with the concomitant increase in temperature will affect the composition and structure of alpine plant communities (Körner
Peters (
This article is a first attempt at a phytosociological analysis and vegetation description of high-altitude alpine plant communities in the Drakensberg, which, using ordination methods, identified four different habitats. It is unknown how species numbers and cover in these habitats may change seasonally as a result of decrease in rainfall during the drier season. The overriding ecological factor is prolonged freezing, the effect of high altitude, followed by high rainfall and, undoubtedly, soil composition and its depth, which play an important part in lower amplitude ecological factors responsible for species richness and diversity. This also confirms within community plant affinities as well as the broader landscape level vegetation clustering.
Legislation is in place to protect the inselbergs on the Drakensberg Escarpment as the Free State Province is in the process of drafting a provincial biodiversity strategy to specifically protect inselbergs.
The fieldwork was supported by the National Geographic Committee for Research and Exploration (grant # 7920-05), without which funds the study would not have been possible. The Principle Investigator thanks the Maluti Drakensberg Transfrontier Project and the KwaZulu/Natal Conservation Staff for assistance with the fieldwork and plant identification. Photographs are courtesy of Richard Lechemere-Oertel, Boyd Escort and Rob Scott-Shaw, who also helped with plant identification in the field and at the Donald Killick Herbarium (CPF). The excellent maps of the study sites where composed by Heidi Snyman of Ezemvelo KZN Wildlife.
The authors declare that they have no financial or personal relationship(s) that may have inappropriately influenced them in writing this article.
R.F.B. (University of South Africa) was the project leader and principle author, N.C. (Free State Department of Economic, Tourism and Environmental Affairs) provided theoretical input and processed the data in Juice, and P.J.d.P. (University of the Free State) contributed 53 relevés and edited the syntaxonomic table presented as Online Appendix 1.