GEOGRAPHICALDISTRIBUTION AND LOCAL OCCURRENCE OF DToHAzETALUMCYMOSUM (HOOK) ENGL. (GTFBLAAR) rN NAMIBIAAND SURROUNDING AREAS

R.I. DE SOUSA CORREIAAND L. YAN RENSBURG

ResearchInstitute for ReclamationEcology, Potchefstroom University for ChristianHigher Education P.O. Box 19752,Noordbrug,2522,RSA

ABSTRACT INTRODUCTION

This paper discussesDichapetalum cymosum's habitat, The family Dichapetaluminclude two genera: coveringits distributionacross southern , , and Tapura.Dichapetalum is representedby about200 spp., Botswanaand South in orderto ascertainit's ecological trees,shrubs and rhizomatousshrublets: cosmopolitan in nicheas delimitedby someclimatological and edaphic factors. tropicalcoutries, rare in sub tropics.There are threespecies From this study the distributionarea of D. cymosumwould o'fDichapetalum in southernAfrica (Dyke 1975). seem to extendfrom the north-westernlimits of the loose Kalaharisands, in southernAngola (Cunene River basin - Dichapetalumcymosum, is a well-knownpoisonous mediumcourse), across north-easternNamibia (Okavango rhizomatousplant endemic to SouthernAfrica, and knownto River basin and the endorreicdry system of various occurin cedain areas of the dry savanna, mostly in the Kalahari omiramba),across (southwest of the Okavango Basin(Dreyer 1975, Smith 1966). lts occurrencehas also Deltaand of the MakgadikgadiPan and northof the Molopo beenreported in Angola(south), (south), andacross the River basins) into , across (west),Botswana (central), Namibia (north-east) and South the Marico/Crocodile,Limpopo, Nyl, Pienaarsand Elands/ Africa(north-west) (Vahrmeijer, 1981). D. cymosumcan be Olifantriver basins. typifiedas a dwarfshrublet with deep-seated,rhyzomatous .The leavesare allternately arranged and are generally The generalecological characteristics of the distributionarea soft and hairywhile the inflorescence,an axillarycyme, of D. cymosumseems to be a sandy,well drained and nutrient produceswhite flowers that developsinto drupaceous fruits. poor soil, low to moderate(400 - 600 mm) rainfalland The leavesare very poisonousto stock,though stock avoid temperaturesranging between a meanmaximum of 36'C and the plantswhen other green herbage is available.The toxicity a mean minimumof -4"C. For most of the area these of the leaveswas knownsince the earlysettlement days. ln "gifblaar" conditionsoccur along the ecotonal area separating formations SouthAfrica the commonname is derivedfrom the of Baikiaea/Pferocarpusfrom formationof Colophospermum toxic natureof the . Amazingas it might seem, the and or Catophractes.This ecotoneis characterizedby the pulpof the fruitis not toxicand the Bushmeneat the pulpof presence of africana, Terminaliasericea, thefruits. The nameof the plantin the nativelanguage in the "Hainomata", "Don't erioloba, spp. and Ochnapulchra, and varies in surveyedarea of Angola is meaning bite width from very narrowat both ends to much wider in the the seed". middlesection. D. cymosumis absentwhen the combined thresholdof -4"C and 400 mm of rain, in sandy soils A second of Dichapetalumoccurs in Okavango: (Rietfontein- Namibia)is reached,while Dichapetalumrhodesicum. lt is verysimilarto D. cymosumin extendsnorthwards outside the range of thesetwo parameters all morphologhicalaspects, but not much is knownabout its intoareas typified by an averagerainfall above 700 mm anda toxicityor lackof it. lt is a very rare speciesonly found in a rockysubstrate. The -4"Ctemperature distribution limitation, restrictedarea. however,still seems to hold. Fromthis it mightbe concluded that frost is possiblyone of the primarycontributing factors Knowingthat in Namibiathe occurrenceof the plantis haltingthe distributionof D" cymosum. Althoughgenerally restrictedto the north-easternpart of the country,which falls occuringin soilof a sandynature there is a smallrange of insidethe KalahariBasin, with soils consistingmostly of variationinside the Kalahariarea and a more important aeoliansands, a set of surveyswere conductedacross the variationinside the Bushveldcomolex in Transvaal.The territoriesof the Kavango,Bushmanland and Hereroland possiblerelation between the pH of the soilon the distribution (west,east and south)to determinethe differentveld types of the plantis stillunresolved. And on the otherside it seems and theirrelationship with the distributionand habitatof the thatbiotic factors can at leastlocallv influence the distribution species.For the benefitof thestock-farming sector, all known of the soecies. occurrenceof the plantare pinpointedand all areaswhere the plantwas not foundare indicated.A generalmap of the 'sdistribution in Namibiaand some detailed regional maps are included,as aresome areas in south-westernAngola and areasof its distributionin Botswanaand SouthAfrica.

AGRICOLA2OOO 1q sand MATERIALSAND METHODS undulatedbecause of the existenceof consolidated dunes,ancient dry river beds (knownlocally as omiramba) plateauis 1200 m, but at 1. Generalprocedure and oans. Mean altitudeof the placesit can reach 1300m up to as much as 200 m above and well Directstudy of some areasof SouthernAngola, Kaokoland, low-lyingomiramba and pans. The mostextensive whichdissects Ovambo,the Easternedge of the CentralPlateau and most definedomuramba is the Omuramba Omatako, endingin the of Kavango,Bushmanland and Hererolandtook placeusing the areafrom the south-westto the north-east, pans, Khabi,are all existingroads and tracksand sometimesusing straight OkavangoRiver. Larger Nye-Nyeand Thereis a marked transectsby compassacross the bush. The botanical situatedsouth of Tsunkwein Bushmanland' sandmantle from the compositionwas notedevery time that changes in vegetation decreasein the depthof the dunesand permanent drainagetakes soiland topography were visible, and this was checked against northto thesouth. The only surface water from the topographicmaps and the distanceswere registeredusing placevia the OkavangoRiver, but very little ends up in the the speedometer. Vegetationmaps of all the areas were dry omirambafrom the Namibianterritory compiledbut they will be the subjectof differentpublications. Okavango. Informationon thevegetation, soils, climate and physiography of neighbouringterritories not visitedwas studiedthrough 4. Glimate existingliterature in orderto derivea completepicture of the globalplant ecologY of the area. The area is generalyhot and dry, with an averagerainfall rangingbetween 350 and 550 mm and mean maximumand -6'C, In 2. The study area minimumtemperatures of 36 and respectively. Namibia,the climateof the surveyedarea is semi-aridand + mm in the north- The regionsurveyed in Namibiacovers an area of sub-tropical.Rainfall decreases from 600 + (Rietfontein- approximately450 km longand 250 km wideextending from east (Kavango)to 400 mm in the south-west gradient the mean annual the OkavangoRiver in the north(Lat. 18'S) to the Rietfontein Otjinene).There is almostno on (34.6'Cat Rundu Districtof the Hererolandterritory in the south(Lat. 22'S) and maximumtemperatures from north to south transitionis different fromthe Botswanaborder in theeast (Long. 21"E) to theedge and32.4"Cat Gobabis),but the seasonal whileat Gobabis of the centralplateau GrootfonteinMaterbergiSteinhausen in inthat in Runduthe hottestmonth is October (Weather 1986). However' the west (Long. 18"E). The total lengthof the distribution it is December Bureau,Pretoria, in winter is higher band. which runs in a north-wesUsouth-eastdirection from the mean annualminimum temperature (-4.5"C),which can be of Angolato SouthAfrica, is approximately3 000 km,with outliers (0.6"C)in Runduthan in Gobabis unusualat Rundu, aroundthe ChobeDepression, in northernKalahari. ecologicalimportance, because frost is occurringbetween the lastweek of Juneand the firstweek of from May to 3. GeomorphologYand drainage July only, while at Gobabis it is common September(Weather Bureau, Pretoria, 1986)' With the exceptionof the southernmostpart of the strip of distribution,in theTransvaal, South Africa, the restof thearea 5. Soils is a flat and sandyplateau at an altitudeof 1100to 1700m' (1941) classifiedthe with no mountainsor largerocky hills. Drainagetakes place ln SouthernAfrica, Van der Merwe groups, whichhe denominated via a few major rivers,e.g. the Cunene,Okavango, Zambezi differentsoils into many oneof into two sub-groups' and Limpopo,and is typicalof semi-aridareas, where some KalahariSands, further sub-divided on Limestone.The of the tributariesare usuallyintermittent rivers' A complex KalahariSands Proper and Kalahari Sands of the KalahariBasin endorreicsystem of ancientriver beds and largedepressions firstsub-group occurs in the central area peripheryof the first. and pansis prominentin Botswanaand Namibia.Slopes are and the secondin a narrowstrip on the and depth of the very gentle towards the rivers and depressions' However, The distinctionis basedon the nature or limestone someof the largerorniramba are deeplycarved in a V-shape underlyinghorizon, with or withouta calcrete paid the distributionof D. acrossthe sandyplains, e.g. Omatako, Daneib, and Eiseb,at layer.Although attention was to the vegetationand least in some sections. cymosumand its generalcorrelation with soils,no systematiccollecting of soilsamples took place. The area alongthe rightbank of the MaricoilimpopoRivers on the SouthAfrican side of the borderis similarto the area 6. Vegetation mentionedabove, but south-eastwardsthe area is rugged' gradientin thata floristic beingcrossed by parallelridges running west/east of which In Namibiathere is a clearvegetation dry savannain northern the Magaliesbergis moreconspicuous. Altitude here varies rich,fairly dense and mediumhigh a more open, shorterand between1360 and 1900m. Kavangogradually merges into floristicpoor formationtowards the south of the region,in the (Hereroland). gradientis discernible ln Namibia- withthe exceptionof the Okavangoriverine land Rietfonteinarea Asimilar areas. form(the flood plain and the alluvialterrace), theAha dolomite from east to west, at least in certain hills(1250 m altitude),and the pansand calcreteoutcrops in was describedin detail Bushmanland,the rest of the area is a monotonousplateau The vegetationof the Kavangoarea Bredenkamp,1987), which of recentaeolian sand which is part of the KalahariBasin' in a previouspaper (Correia and of the tree species Topographically,the plateauvaries from flat to slightly includeda catena of the distribution

AGRICOLA2OOO 20 occurringfrom the OkavangoRiver (the Namibianorthern luderitzii,which is rare to the north,and Combretumimberbe. border)towards the south,across the whole lengthof Namibia but these speciesusually do not occur in sandy soils. lt is and up to SouthAfrica (NorthWest Cape). Excludingthe importantto mentionhere that the tall shrub Ochnapulchra is numerousspecies related to the riverineforest of the also presentat this lowerlatitude, but only in sandysoil. All OkavangoRiver, the maintree species occurring in the north othertree speciesmentioned as beingpresent in the Kavango of the area on the aeolian inlandplateau were: Baikiaea do not occurin thissouthern boundary region of the distribution plurijuga, Pterocarpus angolensis, Guibourtia coleosperma, of D. cymosuminside Namibia. Dialium engleranum, Erythrophleum africanum, Burkea africana, Ricinodendrum rautanenii, sericea, Combretum collinum, Acacia erioloba, Lonchocarpus nels/ RESULTSAND DISCUSSION and Combretum imberbe and the small trees Swartzia madagascariensis, Lannea discolor, pulchra, 1. Generaldistribution ol D. cymosum in Namibia Diplorrhynchoscondilocarpus, Combretumengleri, Strychnos pungens and S. cocculoides. The generaldistribution of D. cymosumin Namibiaaccording to the presentset of surveysis presentedin Figure1, as is As previouslyindicated, from the catenarunning north/south the distributionof D. cymosum in SouthernAfrica according along the Namibia/Botswanaborder, Baikiaea plurijuga to Vahrmeijer(1981). In Namibia,the most north-westerly reachesonly the northernpart of Bushmanland.Pterocarpus verified occurrencewas near Makuzu close to the Angolan angolensisreaches the northern Hereroland,and border in the Kavangoterritory. The area between Makuzu Ricinodendronrautanenil reaches only the middle of and the borderbetween the Kavangoand Ovamboterritories Hereroland(Correia and Bredenkamp,1987). The only tree was not surveyed, nor were the areas of north-eastern speciesfound from the Kavangoto southernHereroland (the Ovambo,where the plant most probablyalso occurs. The RietfonteinDistrict) were: Burkea africana, Terminaliasericea, most north-easterlyverified occurrence was in the vicinityof Acacia erioloba and Combretumcollinum. The only othertree Andara,near the OkavangoRiver. This impliesthat on the speciescommonly found in this southernarea are Acacia northernborder of the Namibianterritory, D. cymosumoccurs

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DISTRIBUTIONMAP OF DICHAPETALUMCYMOSUM IN SOUTHERNAFRICA -Yl '\ '-'- tt:"4*|ry / \,e6{ereffi,1\*ffi \IFJ -r.Eibrpoer.ggoqrnBi*.v{ Figure1. Distribution map of D.cymosumin Namibiaand surrounding areas.

AGRICOLA2OOO 21 Table1. Environmentaland climaticalvariables that delimitthe distributionof D. cymosum(Hook) in Namibiaand surroundingareas

Variable Rangeor limit" Altitude(m) 1000-'1500 Landscape Plain Geology Sandstoneand calcrete Soil Arensols Hydrology Via the Kavangoriver or directlyto the delta;via the CuneneRiver (Atlantic) and/orLimpopo (lndian) Climaticregion Cool to warm savanna Rainfali(annual average, mm) 350-550 Rainfallfrequency (annual average number of dayswith rain) 30-60 Rainfallvariability (average deviation as % of annualaverage) 20-35 o/o Seasonaldistribution of rainfall(rainfall for Octoberto Marchas a of annualaverage) 80-90 Lengffiiltny season(number of monthsper year with more than 50mm of rain) 4-5 Evaporation(Potential annual average, mm) <2800 "C) Annualmarch of temperature(annual average, >20 exceptfrom May to October Durationof sunshine(annual average, hd-l) >8exceptfrom January to May Durationof sunshine(monthly average, hd-1) >8 from May to October oC Maximumtemperature (average daily maximum for the hottestmonth, 32-36 o(, tvtinirnumtemperature (average daily minimum for the coldestmonth, 4-9 Wind (dominantdirection) Northeast Averagewind velocity (ms-l) 3.1-6.0 Percentagewind calm (%) 11.6-24.7 Frequencywind interval(%) 14-22 Mist (annualaverage, number of days) None Mist(monthly frequency, number of days) None Naturalvegetation Differenttypes of savanna *This table was compiledwith the aid of the data suppliedby Van der Merwe (1983) throughoutthe Kavango District. The most south-westerly omiramba),across Botswana(southwest of the Okavango "headwaters" verified occurrencewas at Blignaut,at the of Deltaand of the MakgadikgadiPan and northof the Molopo the omurambaOtsojundu in Hereroland.The area around and acrossthe LimpopoRiver basins) into South Africa, across Summerdownwas not surveyed,but at Otjinenethe presence the Marico/Crocodile,Limpopo, Nyl, Pienaarsand Elands/ of D. cymosum was also verified. The most south-easterly Olifantriver basins. verified occurrencewas around the OmurambaGrootlaagte and the southernmostin this area of the RietfonteinDistrict It can be said that the above mentionedarea forms a narrow was along the SteenboklaagteOmuramba, near the area band runningfrom north-westto south-eastand that it is wherethe roadfrom Talismanis meets the omuramba.In the boundedon itswestern edge by the plateauwhich divides the area south of the Omuramba Rietfontein(also known as drainagesystems of the water courses runningtowards the OkantjoveorAmasib), D. cymosumwas not foundalthough Atlanticand the IndianOceans. In fact,with the exceptionof its isolatedoccurrence is possible.The areawhich has suitable the populationsof D. cymosumoccurring in Angola in the basin ecologicalconditions for its occurrence(as presentedin Table of the CuneneRiver, which drains into the Atlantic Ocean, all 1) is to the east of the farm KoppieAlleen, where the otherpopulations of the plantwere found to occurin the basins southernmostspecimens of Burkea africana and Ochna of drainagesystems linked to the IndianOcean or, as is the pulchrawere found. In Bushmanland,just South of the case in Namibiaand Botswana,in endorreicbasins. From Kavango territory, D. cymosum was very common on the the Ruacanaarea, southwards, the dividingplateau surounds Westerntwothirds of the area. In the easternthird of the area the southwesternarea of the Etosha and then deviates the groundsurface is not coveredwith sand,or onlyvery thinly eastwardsto Tsumebwhere it turnssouth towards Okahandja, so,with the resultthat the plant'soccurence was lesscommon. separatingthe basin of theOmuramba Omatako (draining into the Okavango)from the basinsof the Ugaband Omarururivers 2. Edaphic factors draining,directly into the Atlantic. Furthersouth the dividing plateauruns east to Steinhausen,separating the basinsof i. Physiographyaild drainage the OmurambaEpukiro (running east to the endorreicsystem of Botswana)from the basin of the Nossob (running south The distributionarea of D. cltmosumextends from the north- into the Orange). From there the divisionruns eastwards westernlimits of the looseKalahari sands, in Angola (Cunene acrossBotswana separating the omirambaOkwa (Chapman's Riverbasin - mediumcourse), across north-easternNamibia river) and Natedi (Quoxo), both running north towards the (OkavangoRiver basin and the endorreicdry systemof various MakgadikgadiPan (endorreicsystem) from the systems

22 AGRICOLA2OOO drainingsouth towards the Moloporiver. Across the Molopo of Kavango.The interveningdepressions (omuramba type) and intoSouth Africa, the divisioncontinues east, across the are usuallycovered by a thinlayer of greysand. D. cymosum Witwatersrand,separating the basinsof the Marico/Limpopo was not presentin the centralhigher area of these plateaux and Elands/Crocodilerunning north from the drainage system nor in the bedsof the omiramba. D. cymosumoccurred near of the Molopoand Harts running south. This dividing plateau the depressionson the gentleslope between the deep high developsbetween the altitude of 1400-1600m andis roughly laying sand deposits(plateaux) and the base of the situatedalong the 400 mm isohyet. Earlier, referencewas depressions. However,D. cymosumcan occur at places madeto two mainedaphic factors which could influence the wherethe bedof thedepression is coveredby a layerof sand distributionof D. cymosumfrom Angola to SouthAfrica. On of a certaindepth (Figure2). the one hand, the uniformityof the Kalahariregion, which extendsfrom southern Angola to thearea along the rightbank Physiographicconditions in Namibiaare similar to thatin the of the LimpopoRiver in the Transvaal(the so-called Western south-westernpart of Angola, except for the existencein Lowveld)and on the other hand,the geological,soil and Namibiaof dunesand pansmentioned earlier. But similarly, topographicalmosaic of the Bushveldcomplex and D. cymosumwas usuallyabsent from deep plateauxs, dunes neighbouringformations. With regardto the flat sandysub- and depressedareas without sandy cover like pans and plateau,which develops between 1100 and 1300m of altitude omirambawith exposedcalcrete and/or limestone beds, two differentmicrotophographical features are important:these accordingto Vahrmeijer(1981). Interestingly, there are some are the sanddunes and the depressedareas without a sandy inprecisereferences to the occurrenceof D. cymosumin the layerwhere the calcreteor limestoneis exposed. south-easternpart of Angola,but the authorsdid notvisit this area,and consequently this occurrence can notbe confirmed. Inthe sand mantle, although apparently very uniform, frequent changesin textureand the localsubstrate are of importance ii. Soils as to its influenceon the superficiallayer, that is, the occurrenceor lackof a calcreteor limestonelayer and at what As inAngola, D. cymosumoccurs in Namibiain the vicinityof depth. Besidesthe sand mantletwo other featuresare of the omirambabut usuallynot in the bed itself. lt is alsolikely importance,but only for restrictedareas; the riverinebank to occur patchilyin areas of slightlyundulating surfaces. and the flood plain as well as the eventualoccurrence of Accordingto a reportof AOC TechnicalServices (1967), the dolomitehills. soilsof theomiramba are in generalfiner than the surrounding soils. D. cymosun was also absentin pans with a coarse In the Kalahariarea of southernAngola, there are no dunes cover of reddish-brownsand. The extensive,featureless nor pans, similarto that found in Namibia(Kavango and plateauof whiteigreysands with slopes of 0-1% and Bushmanland).There are, however, some extensive plateaux containingless than 1-2o/oclay in the top 90 cm and were withvery thick deposits of Kalaharisand, usually red/yellowish usuallyalso free of D. cymosum. lt was common to find in colour,very well coveredby a dryforest, similar to the one the planton thegentle slopes towards the depressions,but becauseof changesin the microtopography, this pattern was not constant. Thisvariation in topography was usuallyaccompanied by changes in soil texture and colour. In general,it seemed that the olant occurredin shallowersoils with a higher clay content thanthe deepsandy soils. lt did.however. not occur in the very shallow,compact and clayeysoils (Figure 3). This patternappeared to be the same for the rest of the area, A The Dichapetalum cymosun strip with the exceptionof the B Differencesoflevel from the baseofthe strip to the baseofthe depression( 2 OkavangoRiver terrace and in this case) floodolain. n /\ - T Burkea africana LI Acacia erioloba D. cymosum usually did not occur on the red sandsthat Terminalia sericeq o - typifythe edgeof the highpla- Figure2. Typicaltopographical/ecological occurrence of D. cymocumon the slopesof Kalaharisand dunes teau adjacentto the river nor or plateauxtowards the omirambabeds or depressions.The coloniesoccur along the contourlines with the at the steeper slopes of old width of thesestrips dependant on the steepnessof the slope,being narrower for steepslopes (100m in this dunes. But it occurredon instance)and widerfor gentleslopes (450m in this instance).

AGRICOLA2OOO 23 of 2-3o/oand which have a claY plussilt contentof 3% in the toP 90 cm) and at the undulatedsur- facesinside the featurelessPla- teauwhere changesin sandcol- our may alsooccur. In generalit b) can be said that the occurrence oI D. cymosumacross the range of differentsoils was notcontinu- ous, resultingin no clear distri- butionrelation. Du PlooY(un- dated)also distinguishedfor Bushmanlandsoil types, differing in depthand colour: deeP,me- diumor shallow,being red, Yel- low-brownor greyin colour.But, in agreementwith the above- mentionedconclusion stated that withthe exceptionof someflats, omiramba.pans and the calcar- eous flats aroundTsumkwe, D. cymosumwas distributedover theentire area with the resultthat a link betweenthe local occur- renceof the plant and anY Par- I ticularvariation in soiltype could /\ be established! Baikiaea plurijuga l) - Acacia albida ? p - Baphia massaiensis subsp.Obovata V - Colophospermum It hasbeen said that the southern distributionof D. cYmosumtn - y - o Dichapatelumcymosum Namibiastops north of the OmurambaRietfontein (Herero- land),some 140 km northof the - - Spirostachus africana ? Burkeaafricana * townGobabis. The sandmantle whichextends from the Kavango 6D - s,./.r, carvacaffra fl - Acaciaerioloba I 0 regionto the southernKalahari becomesprogressivelY less * - Lonchocarpus nelsii thick,and south of theRietfontein | - Omurambabed or depression 3 - Transitionzone. This couldbe up to 8km omurambathere are no more 2- Slope: 150-200mwide 4 - Kalahari sandplateau dominated by Baikiaeaplurijuga deep sandy plateauxor high consolidateCsand dunes as Figure3. Catenaryposition of D. cymocumin Angola (northwestern distribution limit ), were:(a) in therare north. However,the initances where Baikiaeapluriiuga occur in combrnationwith Colophospermummopane, D' cymosum foundto the was usuallyabsent from these Mopaneveldareas, (b) were the omurambabed was not far away from a distributionband of D. cYmosum sandyplateau, a sandydepression usually existed between the slopeand sandyplateau with the result extendseastwards from the area and on the slope,(c) the upperomuramba course Ihat b. cymosumtypically occurred in thedepression north of the Rietfontein separatei two sandy plateauxthat were vegetatedwith Baikiaeapluriiuga and the omurambabed was acrossthe Botswana coveredwith sand, D. cymosumwasfound in theomuramba bed (occasionally with shrub like representa- omuramba tives of ColophospermummoPane). borderand acrossto central Botswana.A likelyexcePtion is plateau,where high lyingareas on the catena,with an averageslope of 5% the greatextension of the Ghanzicalcareous andwhichhaveasiltplusclaycontentof4%inthesurface D.cymosumseemstobeabsent.Furthersouth-east,across the most unusual horizons(increasing with depth to about7%), also at a depth the LimpopoRiver into South Africa, around Pretoria' of 90 cm the sandcontent is largelyof the fine sandfraction) occurrenceof D. cymosumis in the area generally but the area rather or on the solonetzsoils (that occupy flat somewhat depressed wherethe soilsare still sandy, geological, soil and areaswith litfle or no slopeand which have a looselayer of representsa mosaic of different Kalaharisands. grey sand loam at a depth of 72 cm, underthe superficial topographicalformations, not relatedto the (1983) having grey/olivehard sandy loam layer),but at the bottomof the This area is classifiedby Van der Merwe as "Grey dunesand riverslopes. However,D. cymosumdid notoccur FerruginousLateritic soils" in the flood plainor at the plateauedge' The occurrenceof onlya stripof areaalong the plantwas much moreclosely linked to the brown{o-yel- The Kalaharisand formation reaches (Vander Merwe,1941)' lowishbrown sands which occupyslighfly flatter or lowerly- the rightbank of the LimpopoRiver is crossedby parallel ingpositions than the redsands (occuring on an averageslope Fromthere, further southeast, the area

24 AGRICOLA2OOO high ridgesof differentgeological and soil formations Park)average rainfall is only229 mm p.a. On the otherhand (Vahrmeijer,1970). Accordingto Vahrmeijer(1970) D. at least in the northernpart, the 400 mm isohyetcoincides cymosumoccurred on the flat areas of the Recentand Ecca with the changein soils from the sandy basin to the rocky formations,as wellas on chert,quartzite, shale and sandstone. plateaumaking it difficultto determinethe respectiveroles of D. cymosumwas absent from igneousformation such as these two factors. The same appliesto the northernand granite(archaic) ferrogabro, gabro and norite. eastern limit of the Dichapetalumstrip which define the occurrenceof D- cymosum.Furthermore, the same problem ln Namibia,Botswana and SouthAfrica the Kalaharisand occursalong the northernand easternlimit of the bandof D. mantleextends far to the southof Gobabisand the Gemsbok cymosum'sdistridution in that above the 600-700 mm isohyet, Park,even reachingthe Gordoniaand Kurumandistricts. there is anotherchange in edaphicconditions and in the Howeverthis entire area is freeof D. cymosum.Here too low generalvegetation. lt is improbablethat the increase in rainfall wintertemperature and/or low rainfall appear to be contributing precludesthe occurrence of the plant.On theother hand, the factorsinhibiting its occurrence. increasingaltitude will balancethe decreasein latitudeand the effectof temperature.In this regardit is interestingto Interms of soilpH, Vahrmeijer (1970) quoted Smatt (1954) by notethat although working in a muchsmaller but varied area "...each saying, speciesor varietyof plantshas a naturalrange inthe Transvaal, Vahrmeijer (1970) found rainfall to be a minor of tolerancefor soil pH, of which the rangemay be wide or factordetermining the localdistribution of the plant. narrow or mediumover differentparts of the pH-scale." Vahrmeijeradded that this principlealso appliesto D. ii. Temperature cymosumin the studyarea. His findingswith regardto pH, obtainedat 102 differentsites where D. cymosumoccurred, It couldbe expectedthat temperatureson top of the central revealedthat the meansoil pH typifyingthese sites was 5.2 plateauin Namibiawould be lowerthan in the sandybasin to rangingfrom 4.2 to 6.4. Accordingto the lastauthor judging the northeast,and thus probablypreclude D. cymosumfrom by the standardsset by Small (1954)D. cymosumcan be extendingsouthwestwards. But the north/southgradient of "Acid{olerant". classifiedas Thisclass of Small(1954) ranges temperaturealong the centralplateau is less markedthan from pH 4.8 to 7.0. This is, however,in disagreementwith alongthe easternlow lyingsandy basin. Along the central Leeman's(1938) findings that D. cymosumoccurs in soils plateau,in the north.Otavi and Grootfonteinhave mean with a pH of 8.0 to 8.5. AOC TechnicalServices (1967) minimumtemperatures of -0.8'Cand -0.4"C respectively and awardeda pH value rangingfrom 4.8 tc 7.9 to areason the -2.8"Cat OkahandjaIn the centre. These minimum terraceof the OkavangoRiver. D. cymosumwas foundedto temperaturesare not likely to precludeD. cymosum occur in those same areas (besidesthe areas of the sand occurrence.Along the sandybasin of the east,Rundu in the plateau). In the same area of the upperterrace (along the northis typifiedby 0.6'C and Gobabisin the centreby -4.5.C. main road betweenRundu and Museseand Runduand The southernmostsite where D. cymosum was found in Mashari,where D. cymosumwas present),Schneider (1987) Namibiawas ca. 140km to the northof Gobabisfor whichno recognisedthree main types of soils (Clovelly,Hutton and temperatureregister exist. Furthersouth, from where D. Oakleaf)all with pH valuesranging from 6.8 to 7.6 (almost cymosumwas absent, along the Namibian/SouthAfrican natural)which differssignificantly from the soils of the borderin the GemsbokNational Park, Mata-Matahas a Transvaalmentioned by Vahrmeijer(1970). minimumtemperature of -7"C: eastwards,Kuruman and Zeerustin SouthAfrica, each reach -4.C whereD. cymosum was absent. lt thereforeseems that in the Kalahariarea severe 3. Climatologicalfactors andfrequent frost might be one of the primaryfactors limiting the occurrenceof the species(Fig a). i. Rainfall 4. Aspect In Namibia,contrarary to expectation,the central plateau does not receivemore rainthan the lower-lyingareas to the north All along the band of D. cymosumfrom Angolato the right andthe north-eastas it couldbe expected,probably as a direct bankof the LimpopoRiver in SouthAfrica, the areais flatwith effectof the cold Benguelacurrent. verygentle slopes towards the drainagelines, with the result that,aspect per se is probablynot an importantdetermining The previously-mentionedoverlapping conditions in the area factor on the generaldistribution of Dichapetalum.However, betweenthe 400 mm isohyetand the long drainagedivision Vahrmeijer(1970) paid great attention to aspectas a variable is very significant,because this isohyetalso forms the lower in his studyarea aroundPretoria, because of its bearingon limitof distributionof D. cymosum,the upper limit being temperature.In his studyarea there were a few highridges, between550-600 mm. Anotherinteresting feature is that while includingthe Magaliesberg,running west to east. He found in Namibiaand Botswana the rainfall decreases from the north- thatnorth facing slopes had morethan 50% of all populations easternedge of the Dichapetalumband to the south-western of D. cymosumthan all otheraspects together, irrespective of edge,in SouthAfrica not onlyis the positioninverted, but the the differentgeological formations and soil types. But, he rainfallis also slightlyhigher. Belowthe 400 mm isohyetin also found that in Recentand Ecca formationsthe olant Namibiaand Botswana,the decrease in rainfallis veryabrupt occurredin flatareas where there was no influenceof asoect. and conditionsprobably become too dry forD. cymosum.For Althoughhis studyarea was only50 km longhe alsonoted a instanceat MataMata, further southwest (Kalahari Gemsbok temperaturegradient in the northernsection of the area,at a

AGRICOLA2OOO 25 slightlylower altitude, was on average3.2"C warmer than the the BankenveldVeld Type no 61 (Acocks,1988), which has highersouthern section where there were no D. cymosum beendescribed as partof the HighveldRegion and saidto be "very immaterialof the geologyor aspect present. There was, frosty". Acocks (1988)do not mentionD. cymosumas however,a widearea to the north-westerncorner of his study beingpresent in thisveld type. Mean maximum temperatures areawhich was also D. cymosumfree. Sincethe geologyof for the entirearea of Vahrmeijer'sstudy varies between 26"C thisarea, mostly igneous in origin (granite, Jamestown igneous and 30"C. Meanmaximum temperatures for some olacesin complex- archaic,ferrogabro, gabro and norite)was different Namibiavaries between 35"C and 36"C. However,it would from that of the areas where D. cymosum occurred on the appearas if Vahrmeijer'sstudy area was too smalland too centraland north-easternsections, which was mostly ruggedfor the analysisof temperaturegradients. In short, sedimentaryin origin (being,chert, quartzite, shale and whith regardto temperaturesit seems to be reasonableto sandstone)it was difficultto separatethe interactiveeffect of assumethat a mean minimumtemperature of between-4oC these two factors. and -6oCwill be the limitfor the occurrenceol D. cymosum from Angola to SouthAfrica. The upper limit seems less Meanminimum temperatures mentioned byVahrmeijer (1970) importantand the overlappingeffect of some otherfactors, for placesin the south of his study area were: -7.7"C for likesoils, and rainfall do notallow for a clearpicture. However, Kalkfonteinand -8.7'C at lrene,while to the northernpart he it seemsfair to assumethat the plantcan survivein areas refersto Onderstepoortas havinga minimumtemperature of with a meanmaximum temoerature of around38"C. -4"C. Furtherto the southof Vahrmeijer'sstudy area, develops 5. Vegetation \::i-r , From the north-westerntip of \{**'"{\ t,g* rtftlr, the band of D. cymosum in \\ south-westernAngola to almost , iii:m ;.' r*l the south-eastern tip in l. Transvaalthe vegetation where theplant is very tr occurs uniform, while on the ecotonalareas thereis morevariation in terms ".'.,.\ of the botanicalcomoosition. The groupof threespecies that occurred more often as

-a.: companionsto D. cymosum 'ir.- consisted of Burkea africana, | ".' ' ,rl'. and Terminalia sericea. Other specieswhich frequently occurred with D. BCcymosum were Pterocarpus - -. I angolensis(higher lying areas with deepersands) and Acacia erioloba(lower lying areas with KEY shallowersands) (Figure4). Dlohrp.trlun oy|norum Also oresentin or near areas 8.lkh.r plurilugs o of D. cymosum were: jc""t A Riclnodcndrcn rrutrn.nil ? Rici n od en dro n ra utan en ii (not Ptarocrrpuarndol,lnaL + in the southern half of the Burl!! rftlcur ? {IStti{t band), Baikiaea plurijuga and Trrmimll! r.l6t il|[t Utlrra Y Gu i bo u ft ia coleo s pe rm a (only in the north). In a broader sense Adansonia digitata, AVEnAO!DLY*I*UI nOnfiC comeer ||(HrN pc) Colophospermummopane ffio W- @* @Ml'n and Acacia albida also occurred E* El"' in the same phytos-sociologic Ll 'r L-l H L_l $,0 L_l 'ro area,although far more rarely and usuallynot side by side. Most of the sites where D. Dichapelalumc cymosum occurred have an itr correlationwith open formation (Burkea africana, Terminaliaserlcea and Ochnapulchra). Thus, it usually Figure4. D. cymosum'sdistribution in Namibiaand its correlationwith some importanttree speciesand did not occurunder dense tree minimumtemoerature.

26 AGRICOLA2OOO stands. When the above-mentionedgroup of specieswas bound by either extensiveareas or outliersdominated by part of a formation of Baikiae plurijuga and Guibourtia Baikiaea plurijuga with Pterocarpus angolensls in sandy coleosperma,which usually forms dense stands (in northern areas to the north-eastof the strip (in Angola,Namibia, areas),D. cymosumwas usuallynot present. Botswana,Zimbabwe and Zambia)where rainfall is higher and by areas dominatedby Colophospermummopane lo ln Namibia,as alreadymentioned, there is a decreasing the southwestof the strip,where the rainfallis lower (in gradientfrom north to south in the numberof tree species Angola,Ovambo and Caprivi/Botswanaborder). Across presentand theirdensities. At the southernboundary of the Botswanathe strip is boundedon both sides by Burkea plant'sdistribution in Namibia(Rietfontein), only five of the africana (Baikiaea plurijuga and Pterocarpus angolensis are twentytree species listed growing in the Kavango, are present. presentat placesto the north-east). Colophospermum These are Burkea africana(rare), Terminalia sericea, Ochna mopaneis absenthere in the outer,south-western edge of pulchra (rare), Combretum collinum and Acacia erioloba. the Burkea africanaformation, south of the OkavangoDelta SinceD. cymosumwaspresent all along the gradient, it implies and the MakgadikgadiDepression, where it is substitutedby that only the above mentionedspecies are of value as Cathophractesalexandri (in limestone areas) and by indicatorsof its presence Althoughit seems that Burkea Combretumspp. and Terminaliasericea (in sandyareas). This africanais now very rare aroundBlignaut and Otjinene,this botanicalcomposition occurs along the 300-400mm isohyet. mightoriginaly not have beenthe caseas thereis evidence fn South East Botswanaand South AfricaColophospermum that poles for fencingthe farms in the area were obtained mopaneis stillpresent but now to the north-eastof the band from Burkea trees. whichis now the areawith lowerrainfall, and is boundto the south-westby Burkeaafricana and Pterocarpus(but now not The findingsdiscussed above are in accordancewith several P. angolensisbut P. rotundifolius),which representsthe area other reportswith regardto speciesthat accompanyD. withhigher rainfall. cymosum.Acocks (1988) stated that D. cymosumoccurs in Transvaal,South Africa, on VeldType no. 18 whichis Mixed At leastin four instancesin Bushmanlandcolonies of D. Bushveldand in associationwith Terminaliasericea, Burkea cymosumgrowing in areas falling outside the edaphic africana, Sclerocarya caffra, Pterocarpus rotundifolius and parametersbelieved to boundthe plant'sdistribution, were "...in Ochnapulchra. And he (Acocks,1988) states: boththese found. Two of thesesites were next to the road-side,along VeldTypes (18b,1 and 18b2)where Burkea africana and Ochna the mainroad between Grootfontein-Tsunkwe-Border (one 10 pulchraoccur together,D. cymosumis likelyto be present; km westand the other30 km eastof Tsunkwe).The thirdone "generaly" (the plant)occurs in VeldType 18b3 and 18b4 was 5 km south-westof the DobePan. On closerinspection "only 'l and patchily"in 8b'1and 18b2". Workingin an of the road-sidementioned above the entirearea, about one overlapingarea, Vahrmeijer (1970, 1981) found a linkbetween hundredmetres on eitherside of the road,showed old signs the habitat of D. cymosum and that of Burkea africana, of previousheavy vehicles movement possibly during the Terminaliasericea and Ochna pulchra. lt should be noted constructionof the road. Outsidethe disturbedarea there that althoughthis area of the Transvaaldiffers significantly was no D. cymosum. lt would,therefore appear that from a fromthe areato the north-west,specificaly with regard to soils smallpossible initial small colony the plantswere spreadby and topography,the main companionspecies remained the the disturbanceof the soilsurface. This could have occurred same. Butthe observationthat this group of species,together through(the buryingof) rhizomesor (fruitsor) seeds. lf the or individually,can occurin otherareas where D. cymosum, disturbancetook place duringthe rainy season,both do not occur indicatesthat certainfactors are inhibitingD. propagationmethods would have been possible. Fromthis cymosumfromoccurring beyond its known boundaries. Galpin scenarioit can be inferedthat the same couldoossiblv have (1926),on the vegetationof the SpringbokFlats, states in an happenedelsewhere. "D. interestingnote: cymosum,the dreaded,poisonous "gifblaa/', occursin a few places(in the SpringbokFlats) in The fourthcase was a lineardistribution along an elephant smallpatches, here and there, in heavysand but is not nearly path,for abouttwo kilometers.All along the path plantsof so frequenton the flatsas in the hillsto the west.lt has been D. cymosumwere found, but noneoccurred outside the path. statedthat this plantis usuallyassociated with Burkea africana On enquiryfrom the Bushmen,the authorswere informed (sering)but I canfind no justification for this statement beyond that elephantsdo in fact swallowthe fruitsbut do not digest the fact that they are both denizensof the heavysandveld. the stones- a plausibleway of spreadingthe plant. The One frequentlyfinds large grovesof Burkeawith no D. Bushmenthemselves also eat the pulpof thefruits and throw cymosumin the neighbourhoodand patchesoI D. cymosum away the stones. The whole strip of distributionof D. with no Burkeatrees anywhere near." lt is interestingto note cymosumfrom Angola to the Limpopois knownto be or to alsothat Du Plooy(undated report, on Bushmanland,Namibia) havebeen elephant migration routes and the possibilityof not only statedthat the associationbetween D. cymosumand such a meansof dispersalshould be considered,at least geelhout(Terminalia sericea) is prominent,but also that on wherethe combinationof the otherfactors, such as soil and the other hand there was a negativecorrelation with climateare appropriate.Du Plooy(undated) also refersto Ele p hantorrh iza ele p ha nti n a. the occurrenceof small patchesof the plant in areas otherwisefree of the plant (kalkveldvlaktesand Tsumkwe ln a broadsense it can be said that the stripof D. cymosum panneveld)without establishing any relationother than that was situatedin an ecologicalniche which is theecotonal area they occurredin deepsands.

AGRICOLA2OOO 27 19B7.A reconnaissance 6. Possible biological control CORREIA,R.l. DE S. & BREDENKAMP,G.J. surveyof the vegetationof the Kavango,South West Africa. ScientificSociety, SWA. JournalXL/XLl. Windhoek, SWA/ Most of the colonies of D. cymosum in Angola were heavily Namibia.'l985/86-1 986/87. infested by small larvae of a certain insect. Although the DlNlZ,A.C. 1973.Caracteristicas mesologicas de Angola.Nova number of larvae (caterpillars) present was not enough to Lisboa.Missao de InqueritosAgricolas, Angola. DU PLOOY,P.J. (undatedreport. Field work done in 1972-73). the , they succeeded in defoliating most of annihilate Ondersoekna die voorkomsvan gifblaar(D. cymosumwat die the plants to such a degree that the risk of the animals eating weidingspotensiaalvan Boesmanlandbei"nvloed. Dept. Bantoe any was greatly reduced. The larvae showed a preference Administrasieen Ontwikkeling,Windhoek. of rangelandin for young leaves. The authors placed one branch of the plant FIELD,David l. 1977a.Potential carrying capacity Botswana.Department ofAgricultural Field Services. Gaborone, four larvae in a plastic bottle overnight and most of the 5- with Botswana. 6 leaves were consumed (Correia 1967). Vahrmeijer (1970) FIELD,David 1.1977b. Range monitoring in Botswana(1973-1977). also refers to the presence of certain larvae in the colonies of Departmentof Agricultural Field Services. Gaborone, Botswana. "gifblaar" in the Transvaal, but he refers to damage done to FROST,P.J.H. 1987. The RegionalLandscape: Nylsvlei in perspective.South African National Scientific Programmes. fruits. lt is obvious that the insects could not eradicatethe the Report133. Pretoria. plants, nor halt propagation by seed as we found colonies GALPIN,E.E. 1926.Botanical survey of the SpringbokFlats '12. everywhere inside its ecological distributionarea. But if one (Transvaal),Botanical Survey of SouthAfrica. Memoir No. can have the plants defoliatedcamp by camp, or area by area, HENKEL,J.S. 1931.Types of vegetationin SouthernRhodesia, Proceedingsof the RhodesiaScientrfic Association. Vol. XXX, the period of young growth (August-September)when during 1931. there is littleother green food available,it would decrease the HARMSE,H.J. VON M. 1978.Schematic soil map of SouthernAfrica number of leaves available for the livestock. Even if new southof latitude1630'5. In Werger,M.J.A. Biogeography and pp.73-75. leaves are formed soon afterwards,the danger might be over Ecologyof SouthernAfrica. Junk,The Hague. HENNING,A.C. and WHITE, R.E. 1974. A studyof the growthand as mentioned in the introduction section, or a new wave of distributionof Colophospermummopane (Kirk. ex Benth)Kink caterpillarscan repeat the defoliation. ex J. Leon:The interactionof nitrogen,phosphorus and soil moisturestress. Proc. Grassld. Soc. St. At. (1974)9. LEISTER,O.A. 1967.The plantecology of the SouthernKalahari. Botanicalsurvey of SouthAfrica. Memoir No. 38. REFERENCES LEEMAN,A.C. 1938.Contribution a L'Etudede D. cymosum(Hook) Engl.et de L'Ecologiedu Transvaal.Bull. Soc. Bot. Gen. 29. ACOCKS,J.PH. 1988. Types of SouthAfrica. Botanical Research SMALL,J. 1954.Modern aspects of pH. London:Bailliere, Tindall & Institute.Dept. of Ag. Tecn.Serv. Pretoria, R.S.A. Cox. (as quotedby Vahrmeijer,1970). AOC TechnicalServices (Pty) Ltd. 1967.A preliminarysurvey of the SCHNEIDER,M.B. 1987. Notes on terrace soils of the KavangoRiver, NaturalEnvironment and the AgriculturalResources of NorthernSWA,/Namibia. Journal SWA Scientific Society. Vol. XL/ Okavangoland.Unpublished. XLI-1985/86,1986,87. Windhoek, SWA/Namibia. CORREIA,R.l. DE S. 1967.Sugestoes para um planoexperimental TIMBERLAKE,J. 1980.Vegetation map of South East Botswana. de Controlee possivelirradicacao de D. cymosum,Angola. Departmentof AgriculturalField Services. Gaborone, Botswana. 'n CORREIA,R.l. DE S. 1976.Main vegetattontypes of Kaokoland, VAHRMEIJER,J.1970. Ekologiesestudie van gifblaar, D. cymosum northDamaraland and sometransects of Ovambo,Etosha and (Hook)Engl. in die Pretoria-omgewing. 'n north-westernSouth West Africa. (Unpublished report). VAHRMEIJER,J. 1970.Rapporl oor reis deur Botswana,2013/ CORREIA,R.l. DE S. 1977.A generalphyto-ecological survey of 1970-6141 197 0. Unoublished. Kavangowith special referenceto veld types and D. cymosum VAHRMEIJER,J. 1981. Gifplantevan Suider-Afrikawat veeverliese ecologyand distributionand a criticalanalysis of farmingability. veroorsaak.Departement van Landbouen Visserye. Unpublishedreport. VAN DERMERWE. 1941 . Soilgroups and subgroups of SouthAfrica. CORREIA,R.l. DE S. 1978a.The main vegetationtypes of SoilsResearch Institute. Science Bull. No. 231. Bushmanlandwith special referenceto occurrenceof D. VAN DER MERWE,J.H. 1983.National atlas of SouthWest Africa cymosum.Unpublished report. (Namibia).National Book Printers. Goodwood, Cape. CORREIA,R.l. DE S. 1978b.The main vegetationtypes of WEARE,PR. andYALALA, A.P. Undated. Provisional vegetatron map Hereroland.Unpublished report. of Botswana. CORREIA,R.l. DE S. 1978c.The main vegetation types of Rietfontein WeatherBureau. 1986. Pretoria. Climate of SouthAfrica. Department (Hereroland).Unpublished report. of EnvironmentAffairs. Pretoria. Gov. Printer.

28 AGRICOLA2OOO