Vegetation of the Brandberg Mountain, Namibia

Abstract

This report forms part of research for Diplom graduation (Master’s thesis) conducted during February to April 2000 on the Brandberg massif in the Central Namib Desert, Namibia. Vegetation and soil was sampled at 53 sites along a 14 km altitudinal gradient following a sampling transect along one of the few climbing routes up Ga-seb Gorge, starting 750 m asl to the Koenigstein summit (2573 m asl). A new method of surveying vegetation in rock dominated, arid mountains was devised for the study. This method involves preferential selection of relevés according to main habitat types occurring (nl. planes, slopes, ravines) and objective recording of rock cover on these sites for numerical analysis. Plant cover-abundance data from 31 relevés was later analysed numerically. 33 species hitherto unknown to occur on Brandberg have been recorded, increasing the total number of taxa to over 520 species. By using DCA and CCA ordination techniques it was shown that altitude and rock cover of habitat are the most prominent ecological variables on Brandberg. Due to the mosaic pattern of habitat, vegetation units are generally found intergrading into each other or forming complex communities at various scales. Classification of vegetation based on physiognomy (growth form) showed four main vegetation types to occur with low to medium densities: · Short Shrubland · Low Bushland · Low Thicket · Herbland and Grassland Based on these types, three vegetation belts (altitudinal zones ) can be distinguished, namely: · Desert and Nama-Karoo at lower altitudes · Savanna at medium altitudes (from app. 1500 to 2100 m asl) · Karoo („shrub steppe“) on the upper mountain Vegetation structure has never been systematically classified for the upper mountain before. The term UPPER BRANDBERG KAROO is thus proposed as a name for this type of shrub steppe. It is composed of taxa found in the inland Savanna as well as the Nama- Karoo and Succulent Karoo characteristically found in the winter rainfall area hundreds of miles to the south. Concurrent existence of species from both summer and winter rainfall areas is a peculiar feature of Brandberg vegetation which is standing in sharp contrast to the surrounding desert biome. Plant communities along the transect have been classified by TWINSPAN analysis. Three main plant communities (associations) were distinguished. These have been divided into nine sub-communities. Segregation of plant communities at primary TWINSPAN level reflects the physiognomic altitudinal zonation, whereas second and third level divisions reflect the habitat characteristics of Brandberg Mountain.