A classification of the vegetation of the Etosha National Park

S. Afr. J. Bot., 1988, 54(1); 1 - 10

A classification of the vegetation of the Etosha National Park C.J.G. Ie Roux*, J.O. Grunowt, J.W. Morris" G.J. Bredenkamp and J.C. Scheepers1 Department of Nature Conservation and Tourism, S.W.A.!Namibia Administration; Department of Plant Production, Faculty of Agricultural Sciences, University of Pretoria, Pretoria, 0001 Republic of South Africa; 1Botanical Research Institute, Department of Agriculture and Water Supply, Pretoria, 0001 Republic of South Africa and Potchefstroom University for C.H.E., Potchefstroom, 2520 Republic of South Africa Present addresses: C.J.G. Ie Roux -

Dohne Agricultural Research Station, Private Bag X15, Stutterheim, P.O. Box 912805, Silverton, 0127 Republic of South Africa t Deceased

4930 Republic of South Africa and J.W. Morris -

Accepted 11 July 1987 The Etosha National Park has been divided into 31 plant communities on the basis of floristic, edaphic and topographic features, employing a Braun - Blanquet type of phytosociological survey. The vegetation and soils of six major groups of plant communities are described briefly, and a vegetation map delineating the extent of 30 plant communities is presented. Die Nasionale Etoshawildtuin is in 31 hoof plantgemeenskappe verdeel op basis van floristiese, edafiese en topografiese kenmerke met behulp van 'n Braun - Blanquet-tipe fitososiologiese opname. Die plantegroei en gronde van ses hoofgroepe plantgemeenskappe word kortliks beskryf en 'n plantegroeikaart wat 30 plantgemeenskappe afbaken, word aangebied. Keywords: Edaphic features, phytosociological survey, vegetation map *To whom correspondence should be addressed

Introduction

The Etosha National Park is situated in the north of South West Africa/Namibia and straddles the 19° South latitude between approximately 14° and 16° East longitude. It has an area of 2,2 million ha and is one of the largest national parks in the world. In the 1960's it was decided to 'develop' the Park as a tourist attraction, and it was realized that an ecological survey was a prerequisite to the sound development of the Park. It was considered necessary: (1) to map reasonably homogeneous units of study; (2) to investigate plant/environment relationships; (3) to study the production of herbage and its utilization in the more important grazing areas; (4) to survey the less intensively used vegetation types and investigate the feasibility of increasing their utilization; and, (5) to study possible developments in the field of tourism. In this paper a vegetation map of Etosha National Park based on the first objective is presented, together with a description of the major vegetation types and soils revealed in the course of the study. The study area

The Park lies in the vast geosyncline into which the Damara supergroup was deposited. Owing to the tectonic stability in the area since then, most of the Park is very flat. Although there are a few inselberge in the area south of the Etosha Pan, it is mainly in the extreme south and west of the Park that there are any hills or escarpments. A range of dolomite hills skirts the Park in the south, and just enters the Park in the west. Here the geological features are more varied and granites, andesites, shales, quartzites and pyroclastic material can be found in addition to the more general limestones and dolomites. In general terms the area south and south-west of the Etosha Pan is a karstveld, with calcrete rubble on the surface. West of the Pan there is an extensive area with calcareous loamy soils and the north of the Park is mainly covered

with aeolian Kalahari-type sands. The first two major soil groups are probably related to shrinking of the Pan, and the aeolian sands are a more recent overburden. The soils in the western regions of the Park are influenced by the range of dolomite hills and the geological components of the escarpment. The temperatures are quite high (the average temperature at Okaukuejo is 22,1°C) and most of the rain falls in the summer months between November and April (Figure 1). There is a pronounced rainfall gradient with rainfall diminishing from about 450 mm in the east to about 300 mm per annum in the west (Figure 2) (Dept. of Water Affairs 1973). The relatively high temperatures, low rainfall and poor soils suggest that vegetative growth is determined largely by the available moisture, although trees may bloom and commence growth before effective rain falls. Drought may cause these early leaves to drop. 'Spring' conditions commence with the onset of the major rainy season in about February. Figures 1 and 2 indicate that the rainfall decreases quite markedly from east to west. In the east, where the rainfall is nearly 450 mm per year, the trees reach 6 m in height, whereas in the west with about 300 mm rain per year, the trees on similar calcareous soil barely reach 2 m in height. Although some of the plant species occur throughout the range of rainfall conditions, there are some which are confmed to either the higher-rainfall (e.g. Spirostachys africana) or the drier regions (e.g. Sesamothamnus guerichiz). The origins of the soils have been discussed by Verster (1980), who also described their nature. The present soil map (Figure 3) is more detailed than Verster's (1980), being based on a larger number of soil profiles. In Figure 3 it can be seen that in the eastern and central regions of the Park a relatively small number of soil classes each cover relatively large areas. In the west of the Park the soils are more heterogeneous. The greater diversity of soils in the western region of the Park as opposed to the uniformity in the east is associated with geological and geomorphological features. Most of the Park lies on the central African plateau, and the underlying geological features of the Damara supergroup have largely

S.-Afr. Tydskr. Plantk., 1988, 54(1)

2

a) Station; b) Height above sea level; c) Mean annual temperature in °C; d) Mean aooual precipitation in mm; e) Duration of observations, of two figures the first indicates temperature, second indiCates precipitation; f) Highest temperature recorded; g) Mean daily maximum temperature of warmest month; h) Mean daily minimum temperature of coldest month; i) Lowest temperature recorded; j) Mean duration of frost free period in days; k) Curve of mean monthly precipitation; I) Curve of mean monthly temperature; m) Months with absolute minimum temperature below 10°C .

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Figure 1 Climatic diagrams after Walter (1973) .

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S. AfT. 1. Bot., 1988,54(1)

3

been covered by an overburden of aeolian sand. The west of the Park lies on the western escarpment, and the geological features of the Damara supergroup, intrusive granites, the Khoabendes group and Basement complex granites are visible. In the Park about 32 ()()() springbok, 9 ()()() zebra, 2 500 blue wildebeest, 725 ostriches, 650 gemsbok and 125 red hartebeest (Berry 1980) are concentrated on about 150 ()()() ha of plain. A further population of at least 500 elephant, 900 kudu, 400 giraffe and 130 eland (Ebedes, Maritz & de Jager 1971) are to be found in wooded areas. There are also some black-faced impaia and roan antelope, chiefly in the Otjovasandu area. Among the carnivores there are 300 to 400 lion, a similar number of spotted hyaena, 70 to 80 cheetah and 1 ()()() to 2 ()()() black-backed jackal (Berry 1980). Methods

Vegetation units were identified on vertical monochrome aerial photographs at roughly 1: 75 ()()() scale and the boundaries transferred to existing topocadastral maps of that scale. In some cases LANDSAT A false-colour infra-red photographs were consulted for additional information. The boundaries were verified in the field as far as possible. These units were later grouped to form what were regarded as major mapping or management units, on the basis of edaphic, topographic, physiognomic and floristic features. The major mapping units were used for an initial grouping of releves and other sampling units in the subsequent Braun - Blanquet type of classification procedure. During 1972 and 1974, 59 stand ('S') samples were taken for ordination studies not dealt with here. During 1975, the vegetation was sampled by 203 sampling units (see Figure 4) using procedures similar to that of the Zurich - Montpellier School of Phytosociology (Werger 1974). Plot size was 20 m

50 km

DOMINANT SOIL SERIES SANDY 51

SOILS

FW

DOMINANT

SOIL SERIES

KARST VELD SOILS

lANGEBAAN (-)

Kl

52 HU

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53 CV

SUNBURY

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KAlKBANK / liTHOSOL

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ZWARTFONTEIN

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56 FW

LANGEBAAN (-)

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K7 AR

ARCADIA

DEEP SOILS OF OYAMBQ PLAINS

II

ES

HEIGHTS

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LANGEBAAN (+)

L3 VA

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Figure 3 Major soil mapping units.

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MISCelLANEOUS LAND CLASSES

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DOlOMrrE/ MARBt£ / CALCRETE

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RHYOLITIC

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ROCK

x 10 m for herbs and 100 m x 100 m for trees and shrubs. If necessary, the areas were increased to give a more repre-

sentative sample. These sampling inventories are referred to as releves. The releve data were synthesized into plant communities using a Braun - Blanquet type of procedure and the computer program described by van der Meulen, Morris & Westfall (1978), and other programs compiled by Kingman (1979). In the following account, the nomenclature of plant species referred to follows Gibbs-Russell et al. (1984). The soils of the'S' sampling units and releves were classified according to the South African binomial soil classification system (MacVicar et al. 1977) (Figure 3). Soils from the releve sites were analysed for: exchangeable cations, pH (H20 and KCI), phosphorus and texture. Soils of the'S' sampling sites were analysed for: first-mentioned two plus clay, silt and sand percentages, electric resistance and carbon in all horizons; and nitrogen and phosphorus in the A horizon (Fertilizer Society of South Africa 1974). For the horizons of the'S' sampling units available soil moisture storage capacity was determined from their depth, salinity and clay content using the graph of du Plessis & Hutson (1974). A moisture index was obtained by multiplying the moisture storage capacity of the soil by the estimated rainfall at the site. Results and Discussion

The constancy values of a selection of species in the major plant communities are given in Table 1. The edaphic features refer only to the upper horizon or layer. The species listed are approximately 171I70 of the total number of species encountered during the phytosociological survey. To be included in Table 1, a species had to be reasonably diagnostic with regard to presence in or absence from a particular noteworthy veld type.

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S. Afr. 1. Bot., 1988,54(1)

Table 1 Synoptic table of major vegetation types Major vegetation types Species groups

A

B

III III III III

I

C

Dl

D2

D3

E

F

GI

G2

H

I. Differential species of tall grassveld communities (mapping units 3, 4 & 5)

Euphorbia inaequilatera Aizoon virgatum Eragrostis annulata Eragrostis glandulosipedata Odyssea paucinervis Indigofera charlieriana Triraphis purpurea Salsola arborea Zygophyllum simplex 2. Differential species of Andoniveld (mapping unit 2) Sporobolus spicatus Eragrostis biflora Craspedorhachis sarmentosa Mariscus squarosa Sporobolus consimilis 3. Differential species of the sweet grassveld on lime (mapping unit I) Geigeria odontoptera Cyathula hereroensis Hirpicium gazanioides Ruel/iopsis setosa

IV IV

II

III

I I

II

II

I

II

III II II

V III III III III

III

III III III III

4. Differential species of Mopane treeveld (mapping units 8, 9, 10 & II) , Vernonia cinerascens Triraphis ramosissima Seddera suffruticosa Calostephane divaricata Aristida rhiniochloa

II

II

IV III II III

5. Differential species of Marula associations (mapping units 12, 13, & 14) Securinega virosa Blepharis obmitrata Spirostachys africana Euclea undulata Acacia nilotica

II I

I III III

II

I

I II

III

I I

IV

I

III

II

II

IV

I

I

III

III

IV

6. Differential species of dolomite inselberge (mapping unit IS) Kirkia acuminata Cissus nymphaeifolia Kalanchoe brachyloba Euphorbia guerichiana Commiphora glaucescens

IV III III III III

7. Differential species of the eastern Karst woodlands Oropetium capense Grewia vil/osa Bidens biternata May tenus senegalensis

III III II II

III

IV III

III III II

II

I I

III

8. Differential species of Kaokoveld (mapping units 25 - 30) Lantana dinteri Aptosimum angustifolium Mundulea sericea Requienia sphaerosperma Grewia retinervis Ptycholobium biflorum

9. Species common to D & E Fingerhuthia africana Boscia foetida Acacia senegal Combretum apiculatum Abutilon fruticosum Anthephora schinzii Eragrostis nindensis Chascanum pinnatifidum Justicia platysepala

II III

II III III III II II

II

I

III II II III III III III II II

III III

III III

II

IV

V

III

I II

IV III II II

IV II

I IV II II III III II

II I

S.-Afr. Tydskr. Plantk ., \988, 54(1)

6 Table 1 Continued

Major vegetation types Species groups

A

Melhania virescens Pupalia lappacea

B

C

Dl

D2

D3

E

II

I

III

I

II

I

II

I

III II

F

GI

G2

H

II IIJ

IV IV IV

IV IV I

II

II III

III III II II III III II II II III

10. Species common to F & G

Commiphora angolensis Tephrosia purpurea Colophospermum mopane (shrub)

II

II

IV

11. Differential species of G. sandveJd

Grewia deserticola Acacia fleckii Terminalia sericea Indigofera daleoides Lonchocarpus nelsii Aristida meridionalis Ocimum canum Acacia ataxacantha Acacia erioloba Merremia tridentata

II

I

II

IV II II

IV

II

II II III III

12. Differential species of western sandveld

Elephantorrhiza suffruticosa Kohautia caespitosa Schizachyrium exile

II

II

IIJ

III II

13. Differential species of eastern sandveJd

Bauhinia petersiana Combretum col/inum

III II

14. Differential species of bottom lands

Acacia kirkii Rhynchosia minima Nidorel/a resedijolia Eragrostis rotijer Corchorus asplenijolius

Thirty-one mapping umts or plant communities (with subdivisions), were recogmzed (Figure 5) and these were arranged in six major groups. There is similarity between the boundaries of some of the vegetation umts and some of the soil mapping umts (Figure 3). The major groups of plant commumties are in some cases named after the most salient pedological or geological feature, as in 'Karst woodlands', 'sandveld areas', and 'shrub-mopane on loamy soils'. Within a group the various plant commumties are frequently separated on the basis of relatively minor pedological features.

A. Tall grassveld communities The Okondeka duneveld, Poachers' pemnsula and Ekuma grasslands (mapping umts 3, 4 and 5, Figure 5) are included in this major commumty. The soils of these commumties are frequently of the Langebaan series (Fernwood), and are of recent aeolian origin. The sands often overlie calcrete and free lime is often present. Most of these commumties are ecologically fragile and it is fortunate that they are not grazed to any extent. The differential species for this commumty are listed in species group 1, Table 1. Woody plants are not prormnent in these grasslands. However, the shrubs Salsola tuberculata, Leucosphera bainesii, Dichostachys cinerea and Catophractes alexandri are locally common. Grass species frequently found in the herbaceous layer include Triraphis purpurea, Monelytrum luederitzianum, Stipagrostis uniplumis, Eragrostis lehmanniana, Eragrostis sabinae, Eragrostis porosa, Enneapogon cenchroides and Enneapogon desvauxii. In the Poachers' pemnsula area, Stipagrostis uniplumis is physiognormcally the most important species, while Aristida adscen-

II

II IJI III IJI

IV

sionis has a high cover in the Ekuma grasslands. Forbs include Hirpicium gazanoides, Zygophyllum simplex, Hermannia modesta, Euphorbia inaequilatera, Kohautia azurea and Merremia palmata.

B. Adoniveld This commumty is represented by mapping umt 2 (Figure 5). The shallow soils of this vegetation type, which is generally found within a metre above the level of the Pan, are quite saline and more or less alkaline with a pH (KCI) of about 8,5. They are of the Heights series of the Estcourt form, and the sodium status of the impervious clay layer is 5 000 to 10 000 ppm. Historically the Andomveld was grazed during the rainy season only. However, owing to the provision of permanent waterholes they are now grazed chiefly during the late dry season when forage is scarce elsewhere. The differential species of Andoniveld are listed in species group 2, Table 1. The most prormnent species in this vegetation type are the very coarse stolomferous Sporobolus spicatus, while Odyssea paucinervia and Craspedorachis sarmentosa are common. In areas from which these grasses have disappeared, probably as a result of grazing pressure or trampling, Aristida adscensionis and Enneapogon desvauxii sometimes occur in almost pure stands. Shrubs such as Indigofera sUffruticosa and Dichrostachys cinerea are locally invading the plains. C. Sweet grassveld on lime Mapping umt 1 (Figure 5) represents this vegetation type. These extensive grasslands, bordering the southern edge of

S. Afr. 1. Bot., 1988,54(1)

7

the pan, constitute the most important grazing land in the Park. These grassy plains are grazed extensively during the rainy season by large numbers of herbivores. During the long dry season, the animals are forced to concentrate near the waterholes, mostly along the southern edge of the Pan, and

these regions become severely overgrazed. The soils of these sweet grasslands are loamy, silty or clayey, usually shallow and underlain by a hardpan, in this case, calcrete. The dominant soil forms and series are lithosols, Mispah form, Kalkbank series; Glenrosa form, Lekfontein

LEGEND MAJOR COMMUNITIES A

I

. ..

5 ::::::: 6 :::::: 7

B

G:::bd

TALL GRASSLAND COMMUNITIES OKONDEKA DUNEVELD POACHERS PENINSULA EKUMA GRASSLANDS OMURA MBA ONAISO KARST VELD TURF PANS ANDONIVELD SWEET GRASSVELD ON LIME EASTERN KARST WOODLANDS MOPANE TREEVELD CMOPANE/CAPICULATUM/TpRUNIOIDES BUSHVELD iiUNGARIES - VEGET ATION MAPPING UNIT MARBLE HILLOCK THAI- TKAB WOODLANDS MARULA ASSOCIATIONS !-PRUNIOIDES/'?AFRICANA WOODLAND DOLOMITE INSELBERGE

1--..........

KAOKOVELD A.REFICIENS/CMOPANEITPRUNIOIDES THORN SCRUB C.MOPANEICAPifOLArUM/S.GUERICHIl BUSHVELD OTJOVASANDU HILLY MOPANE SAVANNA KAROSS GRANITIC MOPANEVELD RENOSTERVLEI CMOPANEICHEREROENSEI .?GUERICHII SHRUBLAND SHRUB MOPANE ON LOAMY SOILS NINETEENTH LA TlTUDE SHRUB MOPANEVELD NARAWANDU SHRUB MOPANEVELD EKUMA WOODLANDS SHRUB MOPANE ON ES HOURT -FORM SOILS

H

Figure 5 Map of vegetation types.

SANDVELD AREAS SANDY SHRUB MOPANEVELD PARADYS VEGETATION MAPPING UNIT SANDY TERI1INALIA ACAOA SHRUBLAND SOUTH-EASTERN SANDY BUSHVELD NORTH-EASTERN SAND VELD WARES SANDY I10PANE ICot18RETlJt1 HEREROENSEI SESAHOTHAt1NUS GUERICHH SHRIJ8LAND 8OTTOf1 LAIIlS SALINE Alii/OR DEPRESSED AREAS

S.-Afr. Tydskr. Plantk., 1988,54(1)

8 series; and Valsrivier form, Lindley series. They generally have a reasonably high cation exchange capacity, with a high proportion of adsorbed calcium and magnesium. They are frequently oversaturated and the pH is high (7,5 to 8,0 or higher, in CaCh). The high salinity may cause physiological dryness . These soils have, as a rule, the lowest available water indices in the Park. They also have high nitrogen levels in the A horizons . The high nitrogen levels may be associated with the occurrence of the blue-green alga Nostoc sp., which is relatively abundant on these saline soils. The differential species for these grasslands are listed in species group 3, Table 1. Although these stands are typically treeless plains, woody plants may be present in localized areas. The more common woody plants are Acacia nebrownii, A. tortilis, A. mellifera, A. reficiens, Aloe littoralis and Albizia anthelmintica. A. nebrownii occurs in extensive thickets . In these situations there may be up to 850 trees per hectare. Catophractes alexandri may also be present but then usually in association with other trees. The more important shrubs are Leucosphaera bainesii,

Cyathula hereroensis, Monechma tonsum, M. genistifolium and Petalidium englerianum. Salsola aphylla forms occasional pure stands and Suaeda articulata is found typically on the saline soils of the Lindley series (Valsrivier form) . Protected sites show that this veld type is quite capable of supporting taller-growing perennial grasses such as Stipagrostis hochstetteriana and Cenchrus ciliaris. However, most of the veld type is at present in a relatively stable dis-climax stage induced biotically by excessive grazing. In this condition the more important herbs are Enneapogon desvauxii, E. cen-

chroides, Aristida adscensionis, Eragrostis nindensis, Euphorbia inaequilatera, Tragus berteronianus, Oropetium capense, Tribulus terrestris, Kohautia azurea, Indigojera charleriana, Eragrostis annulata and Geigeria odontoptera. In the Springbok and Charistsaub Plains areas Monelytrum luederitzianum becomes more important. In the most heavily grazed (Namutoni) area, this relatively stable dis-climax has been destroyed and sheet erosion is taking place. Here Sporobolus coromandelianus is important and in some areas S. spicatus and Geigeria species are physiognomically very conspicuous. On the fertile Lindley series (Valsrivier form), the herb layer has been destroyed and Sporobolus coromandelianus may be important.

D.

Eastern Karst woodlands

These woodlands are situated south of the Etosha Pan and extend westwards. They are usually separated from the saline pans by a strip of sweet grassveld on lime. The soil is generally a calcrete litho sol representing the Kalkbank series (Mispah form) or Lekfontein series (Glenrosa form) . There are a few dolomite inselberge and some outcrops of a low-grade marble. In some areas there is a matrix of calcrete high ground and clayey depressions. , These vegetation types are easily identified by the presence of the differential species listed in species group 7, Table 1. The woodlands are generally mopaneveld Colophospermum mopane, except in the extreme east, where Spirostachys ajricana is prominent in a small area. Near the edges of the pans Colophospermum mopane forms almost pure stands, but further away Combretum apiculatum, Terminalia prunioides and Acacia nilotica become more important as the vegetation becomes richer in species. This greater species richness is related to an increase in the soil's moisture index. Eastern Karst woodlands comprise three major subtypes: (1) Mopane treeveld in the drier western parts (mapping units

8, 9, 10 and 11) on shallow lithosols with coarsely fractured calcrete on the soil surface. (2) Marula associations and Terminalia prunioides/ Spirostachys ajricana woodland (mapping units 12, 13 and 14) in the wetter eastern parts on very shallow soils which overlie calcified dolomite or low-grade marble . (3) Dolomite inselberge (mapping unit 15).

1.

Mopane treeveld and related vegetation

These vegetation types include Mopane treeveld (mapping unit

8), Co!ophospermum mopane/ Combretum apiculatum / Terminalia prunioides bushveld (mapping unit 9), Dungaries vegetation (mapping unit 10) and Marble hillock (mapping unit 11). The soils are similar to those of the adjoining sweet grassveld. Lithosols, representing the Kalkbank series (Mispah form) and Glenrosa form. The calcrete is generally in a coarsely fractured form when superficial. The available moisture indices are generally higher than the grassveld. The differential species of this vegetation type are listed in species group 4, Table 1. In some of the stands, Co!ophospermum mopane may be the sole woody species. In other cases, Catophractes alexandri, Acacia reficiens, Acacia mellijera, Grewia spp., Montinia caryophyllacea, Commiphora

pyracanthoides, Acacia senegal, Boscia joetida, Boscia a/bitrunca, Acacia nebrownii and Gossypium triphyllum may be present in the tree or shrub stratum. The herbaceous layer is quite similar to that of the sweet grassveld on lime (C). In some cases where the soils are even shallower, and where the soil surface is almost completely covered with calcrete rubble, Combretum apiculatum and Terminalia prunioides become more prominent. Here the shrub layer consists of young individuals of the tree species and a few others, such as Commiphora pyracanthoides, Gymnemma sylvestre, Vernonia cinerascens, Grewia flava and Leucosphaera bainesii. The herb stratum is usually poorly developed, probably because the surface is almost pure calcrete rubble.

2.

Marula associations and Terminalia prunioides/ Spi-

rostachys africana woodland This vegetation type includes mapping units 12, 13 and 14 (Figure 5). In the eastern areas with slightly higher rainfall, a further variation of the Karstveld is found, usually on boulder calcrete. The soils are very shallow and overlie a calcified dolomite or a low-grade marble. They are, however, relatively fertile and have nitrogen and phosphorus values of 2 300 and 57 ppm, respectively. The higher-lying areas generally have a few centimetres of heavy clayey soil between the calcrete boulders, which erupt on the surface. The soils of the lowlying areas are typically Arcadia form and series, but one profile was recorded as Swartland form (Broekspruit series). The vegetation is characterized by the differential species listed in species group 5, Table 1. Colophospermum mopane and Terminalia prunioides are the most important trees. Towards the east, Spirostachys ajricana becomes more important and can have importance values of about 15070 in the tree stratum. Securinega virosa, Gymnemma sylvestre and Euclea undulata are quite frequent additions to the list of shrubs . The herb stratum is fairly well represented and has a high proportion of perennial grasses e.g. Eragrostis nindensis. On some sites, Commiphora pyracanthoides becomes prominent forming a dense canopy with Cenchrus ciliaris in the herb stratum having a canopy cover of usually more than 1%. The typical T. prunioides - S. ajricana woodland near

S. Afr. J. Bot., 1988,54(1)

Namutoni is distinguished mainly by the absence of Colophospermum mopane, and the presence of Combretum imberbe and Ximenia americana, although both these species may occur elsewhere. In these woodlands, Terminalia prunioides becomes dominant, while Spirostachys africana, Acacia rejiciens and Dichrostachys cinerea may also be important. The trees are up to 6 to 7 m tall. There are approximately 475 trees and 3 450 shrubs per hectare. The herbaceous layer consists mainly of annuals.

3. Dolomite inselberge There is a range of Otavi dolomite inselberge along the southern boundary and in the western Otjovasandu area. There are also a few isolated outcrops, as in the Halali area. The Otavi group dolomite outcrops are bare rock with a very small amount of soil in the fissures or cavities. The soils generally have very high phosphorus values (more than 90 ppm). Differential species of this vegetation type are listed in species group 6 in Table 1. The vegetation of these inselberge is characteristic as regards composition and structure. Kirkia acuminata, Cissus nymphaefolia, Moringa ovalijolia and Euphorbia guerichiana which are relatively rare elsewhere occur on most of these sites. Other common trees are Terminalia prunioides, Combretum apiculatum, C. mopane and in some areas Sclerocarya caffra.

E.

Kaokoveld

In the extreme west of the Park the geological and geomorphological nature of the terrain change abruptly. Although much of the material is still calcareous, there are large areas of rhyolitic, andesitic and granitic origin. This large area is mainly mopane veld representing the following mapping units (Figure 5). Mapping unit 25 - Acacia rejiciensl Colophospermum mopanel Terminalia prunioides thorn scrub. Mapping unit 26 Colophospermum mopanel Combretum apiculatuml Sesamothamnus guerichii bushveld. Mapping unit 27 Otjovasandu hilly mopane savanna. Mapping unit 28 Kaross granitic mopaneveld. Mapping unit 30 Renostervlei Colophospermum mopanel Combretum hereroensel Sesamothamnus guerichii shrubland. The differential species of the Kaokoveld are listed in species group 8, Table 1. Species group 9 indicated the floristic relationships between the Kaokoveld vegetation type and the eastern Karst woodlands . In some areas the soils are very similar to those of eastern Karst woodlands, i.e. very shallow lithosols on a calcrete substrate. Here Acacia rejiciens, Terminalia prunioides and especially Colophospermum mopane are dominant. Shrubs of Gossypium triphyllum, Boscia foetida, Monechma genisitijolium, Petalidium englerianum and Leucosphaera bainesii are also frequently found. A sheet of aeolian sands locally covers the calcrete boulders. On these sites, Sesamothamnus guerichii, Catophractes alexandri, Otoptera burchellii and Mundulea sericea also become prominent. The herbaceous layer is well developed here, with Anthephora schinzii, Enneapogon desvauxii, Stipagrostis hirtigluma and Enneapogon cenchroides prominent. On the hilly areas on the andesites of the Khoabendes group, the lithosolic soils are relatively fertile. In addition to the dominant Combretum apiculatum,

9

Terminalia prunioides, Colophospermum mopane and Sesamothamnus guerichii, the shrubby Lantana dinteri, Vernonia cinerascens, Indigofera texeirae, Euphorbia guerichiana and Montinia caryophyllacea may be present. The herbaceous stratum is perennial with Eragrostis nindensis very prominent. Other prominent grasses include Anthephora pubescens, Triraphis ramossissima, Stipagrostis hochstetteriana, Fingerhuthia africana, Stipagrostis uniplumis and Aristida adscensionis. On the relatively acid soils of granitic origin in the area, Schmidtia kalahariensis and Microchloa kunthii become prominent, while the clay loam soils of the Clovelly form above the edge of the escarpment carry Combretum hereroense and Sesamothamnus guerichii. Here Eragrostis annulata, E. nindensis, Anthephora pubescens and Aristida adscensionis are of the more prominent species.

F.

Shrub mopane on loamy soils

This vegetation type comprises mapping units 21 to 24. Mopane trees and shrubs occur over an extensive area in a region commonly called the nineteenth latitude. On the aerial photographs this area was characterized by the presence of small depressions. There are four or five distinct physiognomic types in the area but the boundaries between the types could frequently not be identified on the aerial photographs. In the region under discussion, the more common soils belong to the Estcourt form, Valsrivier form, Fernwood form (Langebaan series) and the Arcadia series. The area has a loamy substrate or, if it is sandy, the clay content is reasonably high and the calcium content is also high. The depressions are characterized by their soils which belong to the Arcadia form and series. Although the occasional tree may occur in these small pans (often on termitaria), they are typically open grassy patches. The most conspicuous grasses are Eragostis rotijer and Bothriochloa radicans. The shrub mopane vegetation on loamy soils has no differential species, but can be distinguished from other vegetation types by the presence of species group 10 in the absence of species group 11. Colophospermum mopane in shrub form is clearly the dominant species. Other species include Catophractes alexandri, Leucosphaera bainesii, Dichrostachys cinerea and Grewia jlava. Prominent species in the herbaceous layer include Aristida adscensionis, A. rhiniochloa, A. hordeacea, A. effusa, Geigeria acaulis, Pogonarthria jleckii, Hermannia modesta, Monelytrum luederitzianum, Stipagrostis uniplumis, Heteropogon contortus and Limeum fenestra tum .

G.

Sandveld

There are areas of deep Kalahari-type sand in the north-east and north-west corners of the Park. The sand in the west is finer than that in the east indicating that it was transported farther than the eastern sand. In the extreme west the sand is also shallower than that in the east, and the underlying calcrete is exposed in some western situations. The western parts are also markedly drier than the eastern parts. The sandveld covers mapping units 16, 17, 18, 19, 20 and 29. A large number of species occur almost exclusively in the sandveld. Differential species are listed in species group 11, Table 1. Two major sub-vegetation types are distinguished: (1) Dry western sandveld. (2) Relatively wetter eastern sandveld.

1. Dry western sandveld Differential species for the drier vegetation type are listed in species group 12, Table 1. On the shallower sands in the west

S.-Afr. Tyd8kr. Plantk., 1988, 54(1)

10 of the Park, shrub mopaneveld occurs. Here Colophospermum mopane is the prominent woody plant, while Leucosphaera bainesii, Seddera sujjruticosa, Rhigozium brevispinosum and Commiphora angolensis are often present. Grasses include A n theph ora pubescens, Pogonarthria jleckii and Eragrostis dinteri. On some sites where the soils are deeper (Paradys vegetation, mapping unit 17), Terminalia sericea becomes prominent, while Acacia erioloba, Dichrostachys cinerea and Croton gratissimus may also be present. In local depressions, especially on the Hutton or Clovelly form soils, Acacia rejiciens is conspicuous. Important herbs on these sites include Schmidtia kalahariensis, Eragrostis lehmannia, Acanthosicyos naudiniana, Fimbristylis exilis and Aristida meridionalis. 2. Wetter eastern sandveld This vegetation can be identified by the presence of the differential species listed in species group 13. The soils are deep kalahari sands or coarse acid sands on fractured sandstone of the Nosib group. The woody plants in this vegetation type are dominated by Terminalia prunioides, T. sericea, Croton menyhartii, Lonchocarpus nelsii, Grewia jlava, Combretum col/inurn, Bauhinia macrantha and Ochna pulchra. Important herbs include Schmidtia kalahariensis, Digitaria pole-evansii, D. perottetii, Oxygonum alatum and Hirpicium gorteroides.

H. Bottomlands Several communities occur scattered throughout the Park in slightly depressed areas and similar situations. The soils in these situations are typically Arcadia series (Arcadia form) and similar clayey soils, usually with free lime. In some cases the individual communities were large enough to map separately but usually this was not the case. Plants that often indicate these situations are Acacia kirkii, Acalypha spp., Rhynchosia spp., Eragrostis rotijer, Corchorus asplenifolius and others. I. Saline pans The Etosha Pan and the other saline pans comprise the largest single 'vegetation' unit in the Park. Their combined area is almost one quarter of the total area of the Park. These pans are largely without vegetation. Ostriches nest on the Pan, as they are afforded some protection from scavenging jackals. In seasons when water is available, flamingos (Jensen & Clinning 1976) and pelicans breed or nest on the Pan. The soil is a whitish clay which cracks into hexagonal fragments on drying. The pH is very high (8,18 to 10,2) and the sodium content is in excess of 30 000 ppm. Higher plants are rare on the Pan although in a year of above-average rainfall Sporobolus salsus may be present especially near the edges (e.g. Homob). On smaller hummocks Suaeda sp. may be found. 'Islands' of vegetation, mainly Sporobolus salsus, form on the larger hummocks.

Conclusions The Etosha National Park has been divided into a number of major vegetation types using floristic data and these can

be equated with mapping units (see Figure 5) that are relevant for management purposes.

Acknowledgements The authors wish to thank all individuals and organizations that provided support in various ways. The Administration of South West Africa/Namibia funded a major part of the study as Research Project 31 of the Division of Nature Conservation. The Soils and Irrigation Institute analysed some 100 soil samples free of charge, and Mr Louis Sim arranged the same for some 300 soil samples. Mr Buys of the Fertilizer Society arranged that the Citrus Exchange analyse some soil samples free of charge. The Botanical Research Institute identified plant specimens and supplied computer facilities . Dr Eben Verster classified the soils of 59 profiles. Mrs J. Schaap of the Botanical Research Institute helped to finalize the figures for publication.

References BERRY, H.H. 1980. Behavioural and ecophysiological studies on blue wildebeest (Connochaetes taurinus) at the Etosha National Park. Ph.D. thesis, Univ. of Cape Town. DEPARTMENT OF WATER AFFAIRS. 1973. Rainfall isohyets for South West Africa. Dept. of Water Affairs, Windhoek. DU PLESSIS, H.M. & HUTSON, J.L. 1974. Soil and water in irrigation . The Citrus and Subtropical Fruit Journal July: 4-11. EBEDES, H ., MARITZ, N. & DE JAGER, M. 1971. Interim report on aerial counts of wildlife in Etosha National Park. Unpublished progress report, Project 28, S.W.A.A. Windhoek . FERTILIZER SOCIETY OF SOUTH AFRICA. 1974. Manual of soil analysis methods. FSSA Publication No. 37. GIBBS RUSSEL, G.E. AND THE STAFF OF THE NATIONAL HERBARIUM 1984. A list of species of southern African plants. Mem. Bot. Surv. S. Afr. No. 48. JENSEN, R.A.C. & CLINNING, C.F. 1976. Birds of the Etosha National Park. Division of Nature Conservation and Tourism, S.W.A.A. Windhoek. KINGMAN, E.R. 1979. Programmes to improve readability and sort data on departmental computer. (Unpub\. Agricultural Research Station, Dohne). LE ROUX, c.J .G. 1980. Vegetation classification and related studies in the Etosha National park. D.Sc.(Agric.) thesis, Univ. of Pretoria. MACVICAR, C.N., DE VILLIERS, J.M., LOXTON, R.F., VERSTER, E., LAMPRECHTS, J.J.N ., MERRYWEATHER, F.R., LE ROUX, J., VAN ROOYEN, T.H. & VON HARMSE, H.I. 1977. Soil classification: a binomial system for South Africa. Department of Agricultural Technical Services, Pretoria. VAN DER MEULEN, F., MORRIS, I.W. & WESTFALL, R.H. 1978. A computer aid for the preparation of Braun - Blanquet tables. Vegetatio 38: 129 - 134. VERSTER, E. 1980. Die aard en genese van die gronde van die Etoshawildtuin, Suidwes-Afrika. Proc. 9th Congo Soil Sci. Soc. sth. Afr. pp. 116 - 123. WALTER, H. 1973 . Vegetation of the earth in relation to climate and the eco-physiological conditions. Springer, New York. WERGER, M.I.A. 1974. On concepts and techniques applied in the Ziirich-Montpellier method of vegetation survey. Bothalia II: 309 - 324.