INTRODUCTION

HISTORY OF VEGETATION STUDIES IN SOUTHERN AFRICA

Historically the most notable study of the vegetation of southern Africa was the work of J.P.H. Acocks. His initiatives in the 1940's and 1950's to document and map the vegetation of South Africa had a significant effect on ecology in the country. Acocks' classification, known as Veld Types of South Africa, soon became the standard reference by which ecologists, farmers and other students of natural systems referred to the indigenous vegetation of South Africa.

Despite the value of Acocks' 'Veld Types', it has remained substantially unchanged since it was first published about fifty years ago. Therefore an up-to-date appraisal of the vegetation of southern Africa is needed. As an interim measure in 1992 a group of South African botanists, under the auspices of the South African Association of Botanists (SAAB) initiated the production of a revised vegetation map of South Africa based on vegetation structure and species composition. The 'SAAB Map' with its accompanying booklet was published in 1996. The map and booklet were aimed at filling the particular need of schools and tertiary education institutions for information on southern African vegetation. The question remains whether this map fulfils the requirement for a definitive map of the vegetation of southern Africa?

VEGMAP - A NEW INITIATIVE

A collaborative initiative entitled the National Vegetation Map of South Africa Project or VEGMAP is now in progress to satisfy the need for a new, definitive map of the vegetation of southern Africa. Funded by the Department of Environmental Affairs and Tourism (DEAT) the project is managed by the National Botanical Institute (NBI) and is targeted for completion by the end of 2001

. The VEGMAP is not a revision of Acocks' 'Veld Types' but an entirely new project, the aims of which are (i) to determine the variation in and units of southern African vegetation based on the analysis and synthesis of data from vegetation studies throughout the region and (ii) to compile a vegetation map. The map must accurately reflect the distribution and variation in the vegetation and indicate the relationship of the vegetation with the environment. For this reason the collective expertise of vegetation scientists from universities technikons and state departments has been harnessed to make the project as comprehensive as possible.

DATA SOURCES

The ACKDAT database

VEGMAP data

In order to make the VEGMAP database as representative as possible, as many vegetation scientists as possible throughout South Africa have been contacted and copies of their data requested for the database. These data will be loaded into a secure database separate from the ACKDAT database but compatible with it. This will preserve the integrity of the separate databases.

Minimum data requirements

· The first requirement of the VEGMAP project is floristic data. Floristic data are lists of plant species taken at sample sites or relevés of variable size (determined by the type of plant community). Data of this kind are most often collected in different formats by different research workers and so the first important step is to standardize the data. When standardizing, taxonomic compatibility of data (i.e. the same name used for the same taxon) is the primary aim and must be achieved before analysis can start.

· Secondly, relative cover and abundance ratings should be made compatible across surveys. This, however, is less important since 'presence/absence data' is also acceptable. The analysis would hinge more on the floristic composition of stands of vegetation than on the relative abundance of the species concerned.

· The third requirement is an accurate record of the locality of a sample. The latitude and longitude of each sample location is necessary to locate and relocate sample positions. This information will be entered into a geographic information system (GIS) database which will ultimately facilitate mapping the vegetation.

Data capture

A database package TURBOVEG has been designed specifically for entering vegetation data and is now available in a Windows® version TVWIN. The package is linked to the floristic lists of a country or geographic area as required. It has an automatic species-lookup procedure which enables relevé data (species lists with cover/abundance data) to be rapidly loaded into a database. In the southern African context TVWIN is linked to the Plants of South Africa database (PRECIS) consisting of about 24 000 species. Efficient species-data accession and checking and rapid loading of relevé data to a database of southern African vegetation samples is now in progress. The TVWIN computer package has been adopted as the standard database package for the VEGMAP project. In this way it will be the 'common denominator' for vegetation data accession to a single database. Data from sources such as databases in other packages can also be transferred to the TVWIN system and files in the Cornell Condensed Format can be readily imported into the database.

Classification of floristic data

The classification of large sets of vegetation data requires that the data are reduced in some meaningful way for efficient handling during analysis. With modern computing capacity it is conceivable to analyse huge data sets but the variation within such data sets may prove unmanageable. A proposal is therefore to make an decision to split the data into 'blocks' along some predetermined lines. The most obvious primary classification would be on the basis of biomes or natural regions. It is proposed that 'working groups' of vegetation scientists should be established in each biome to handle the data analysis and mapping.

With the establishment of a 'common' database, the companion program to TVWIN known as MEGATAB will be used to classify the data. This program uses TWINSPAN for analysis but has some rapid routines that greatly facilitate classification of the data sets.

Within each biome the accumulated data will be classified to produce units of vegetation. These units will be analysed together to produce an overall classification of the vegetation of southern Africa.

Ordination: relating vegetation units to the environment

The vegetation of southern Africa reflects the interaction of a large number of environmental factors the most important of which are climate and soil type (geology). No classification or map of the vegetation would be complete if these factors were not considered. Where possible environmental data will be obtained that will be used in conjunction with the vegetation data to investigate the gradients in the landscapes. The ordination of the data will be done using Canonical Correspondence Analysis (CCA) where the analysis of the vegetation data is constrained by the environmental data. This 'direct gradient analysis' method will enable the interpretation of the vegetation units in terms of their habitat and will facilitate the development of models for extrapolation of vegetation units. This procedure together with the classification will greatly enhance the accuracy of mapping the vegetation.

Mapping

Once the vegetation units have been determined from analysis of the data the mapping can take place. Preliminary maps will be prepared using a proprietary GIS package. These maps will then be checked and 'ground-truthed' to ensure accuracy of boundaries. Ground-truthing will involve use of satellite imagery as well as physical checking of boundaries in the field, particularly where sampling has been inadequate. This will involve a 'Rapid Assessment Programme' which is still to be developed. The final map will then be prepared.

Products of VEGMAP

The principal products of VEGMAP will be a new, definitive map of the vegetation of southern Africa and a handbook containing up-to-date descriptions of the vegetation. Additional information about each vegetation unit will include its extent, conservation status, environmental descriptors, special features and economic value. Future possible products will be a CD-ROM disk version of the map and descriptions of the vegetation. The VEGMAP database and electronic version of the map will be held by the National Botanical Institute and will be available for consultation on request.