Expedition no. 5: Tree Society outing to the Bubi River: 18 Apr 2000-24 Apr 2000

The Tree Society of Zimbabwe paid a visit to the Bubi River. Extensive damage had been caused to the river and the adjacent riverine vegetation by Cyclone Eline in February 2000.


Generate a list of species for Expedition no. 5

Description

Tuesday, April 18

We travelled down on Independence Day via Masvingo and arrived at Three Ways Safari camp in the afternoon. The camp is on the southern bank of the Bubi River, c.8 kms E of the main road bridge on the Masvingo / Beitbridge Rd.

Although the camp is 6 metres above the sandy river bed, the water had risen 8 metres at its height, submerging the camp to just below roof height. Damage was extensive. The traditional pole and dagga huts were mostly still standing but with poles only while the more substantial buildings had generally been swept away. However, the kitchen and 2 huts had been refitted and a tent put up, no ground sheet but real beds, and rebuilding was going on.

We (the Hydes) are hardy and we were going to camp, until we discovered that after our last trip our tent (like the Red Sea) had divided into 2 parts and we only had the fly sheet. We might have given the stars a go except for the fact that there was still rain around. So we bagged one of the washed out huts and so had a room with a view on all sides through the poles.

Right up to the last few days, many doubts and fears had been raised about this trip, possibly the most serious being the fuel shortage which had been so bad in March; the possibility of marauding war veterans (we checked with the CFU before leaving) and, not least, the very severe damage which had been done to the camp. Luckily, we were able to leave Harare with the two tanks of our Landcruiser full (180 l) in all and we managed to get diesel (or at least some) in both Chivhu and Masvingo. After a few days, diesel became available at the Bubi village and we were able to fill up every morning.

Seven of us came down from Harare (Maureen, Rose, Andy and 4 Hydes) and we were joined by Jonathan Timberlake and son, Tom, aged 7 from Bulawayo. Later, Adele Hamilton-Ritchie joined us with a friend on the way back from South Africa.

Mark and Linda Hyde

Wednesday, April 19

The first day was spent locally as Mark wanted to try and find a plant recorded from by the railway bridge. This is an exotic "gooseberry", Physalis viscosa, which was discovered by Bob Drummond some years ago. We therefore found the service road along the railway line and headed down this (knowing the railway line was still closed due to bridge problems on the South African side). Unfortunately the road was still transected by a large murky pond from which acacia bushes rose like green boats. We therefore took to our feet and walked along the railway line.

Jonathan showed us Acacia tortilis subsp. heteracantha and explained the differences between the two subspecies. The morphological differences are that heteracantha has pods in tighter coils than does spirocarpa and its pods lack the fine red glands on the pods which spirocarpa has. Ecologically, heteracantha occurs in generally disturbed habitats and is often found away from rivers; it is the usual subsp. in the south and west of Zimbabwe, whereas subsp. spirocarpa is the common one in the north and is usually associated with rivers.

Linda then took the boys walking along the Bubi River bed towards the Lion and Elephant. The river still had water flowing in it, water so clear that from 40 feet up on the bridge schools of small fish could be seen darting about in the deep furrows scoured by water upstream of the pylons. Being a seasonal sand river they were free from fears of hippo, croc and bilharzia and so could enjoy the walk more than some of the trails in the Zambezi Valley. They floundered in mud up to our knees, padded quickly across hot sands, marvelled at the height of the banks, watched the grains of sand tumble down stream, identified to the best of our imagination foot prints and created tracks where no man since the flood had walked before. It took them just over 2.5 hours to do just over 1 km.

The vegetation along the railway line and by the river was typical of low or medium altitudes (Colophospermum mopane, Croton megalobotrys, Faidherbia albida, Grewia bicolor, Hyphaene sp., Justicia flava, Pergularia daemia and Schmidtia pappophoroides) with a noticeable weedy component (e.g. the two grasses: Cenchrus ciliaris and Pennisetum setaceum). A very striking tall grass with an apical cluster of whitish racemes was seen which was new to me; this turned out to be Chloris roxburghiana. Two species of Commicarpus were found: both the fairly common plumbagineus and the rarer (and new to me) pilosus.

However, there was no sign of the Physalis so we drove round to the Lion and Elephant to await Linda and the boys. Near the somewhat damaged road bridge, some fine specimens of Flaveria bidentis were found. Two species of Flaveria occur in Zimbabwe; both are exotic and hail from tropical America, the commonest one seen generally, including around Harare, is F. trinervia whereas F. bidentis appears to be confined to the southern division.

In the afternoon, we parked the cars by the road into the camp and walked up a low hill. The vegetation here was very different to the alluvial stuff around the camp. Trees seen included: Adansonia, the ubiquitous Colophospermum mopane, Combretum apiculatum, Commiphora africana and C. glandulosa, Gardenia resiniflua, Kirkia acuminata, Lannea schweinfurthii, Ochna inermis, Ptaeroxylon obliquum.

A spiny shrub defeated us and there was much debate as to what it was. We finally settled tentatively for the var. natalensis of Ximenia caffra. However, this turned out to be quite wrong - it was in fact Maytenus putterlickioides, a species we had hoped to see for many years but had never done so. Botanical opinion nowadays is to put the spiny species of Maytenus into Gymnosporia, so this would become Gymnosporia putterlickioides.

The ground flora was also of great interest. A yellow-flowered succulent species with prostrate stems was determined as Portulaca collina and may be new to the S division. Very common was a low shrubby Acanthaceae with long red corollas - Anisotes rogersii. A tall, striking parasitic Scrophulariaceae with purple fls and purplish stems was Striga gesnerioides. Fairly common throughout the area and seen frequently on other days was a herbaceous Euphorbiaceae covered in stellate hairs, Cephalocroton mollis.

Back at camp, the boys and Linda took their lives in their hands - or so it seemed - and swung on the swing. A long rope tied high above the river to a "Rain Tree" - Philenoptera violacea (Lonchocarpus capassa) - the bottom was a large loop into which you put one foot and swung out over the river bed - a 5 second trip which seemed to last for hours and would beat anything Disney had to offer in Swiss Family Robinson.

Mark and Linda Hyde

Thursday, April 20

On the Thursday, en route to Chiturapadsi to try and track down the infamous, elusive Triceratella drummondii, we stopped off to look at the southeastern footslopes of Marungudzi "mountain", situated at the edge of Diti communal land and Kayansea commercial ranch east of Beitbridge. Marungudzi, considered sacred by the local Venda population such that one needs chiefly dispensation to climb it, rises abruptly from the generally flat low mopane woodland around. When the sun is right, one can see the rocks glinting pinkish showing that the upper part of the hill is composed of quartz syenite, the same rock that forms much of the nearby Mateke hills, the Hillside area of Bulawayo South and Mt Mulanje in Malawi. In fact, the Marungudzi "alkali ring complex" is well known geologically and is almost unique in the country. It is said to have been intruded around 190 million years ago and contain various rare minerals, although none of economic interest.

However, what we had come to see was the area of black cracking clay soils to the south east of the hill. These were very clearly visible on the satellite images we had and appear different from other, more common areas of black clay soils associated with another rock type, basalt. Careful study of both satellite image and geological maps suggested that these soils were possibly derived from a base-rich igneous rock called gabbro, which is rare in Zimbabwe. In southeastern Botswana black cracking clays derived from gabbro support such low shrubby Acacia species as A. tenuispina and others of the so-called "glandular complex". We wanted to see if this, or other species adapted to these nutrient-rich (in both calcium and magnesium) but difficult soils, were present.

Clay soils composed of montmorillonitic clay minerals, sometimes termed black cotton soils, have a distinctive attribute of being "self-churning" or "self-mulching". When dry they crack to a depth of quite a few centimetres, into which organic matter falls or is blown. With the onset of the rains, water pours into the cracks and the soil swells, incorporating the humus. Very difficult soils to plough, like cement when dry and terribly sticky and heavy when wet. And also very difficult for woody plants. The alternate drying out followed by strong churning forces on swelling shear the roots of most woody plants. This "self-pruning" means that only those species with strong tough roots, such as some Acacia species (particularly A. nilotica and some members of the glandular complex), Dichrostachys, mopane and Dalbergia melanoxylon, can survive. And even they are generally stunted as the roots cannot penetrate deeply. Grasses, being very shallow-rooted (usually only extending down 10-20 cm), survive well. Such soils also support many leguminous herbs. But in general these cracking-clay areas are species-poor, particularly as regards the woody flora.

What we found at Marungudzi was an area of fairly shallow black to dark brown cracking clay, but not as black or cracking as we expected or like the "sidaga" grasslands of N Gokwe and Busi. The patch formed a cap on top of an almost-imperceptible rise, whereas normally clay soils are found in depressions. The vegetation was a low mopane woodland, 2 to 4 m in height, with more open patches where the soil was thinner owing to outcropping rock. Scattered trees of mopane and Lannea schweinfurthii were noted on what appeared to be old eroded termitaria. There was a lot of shrubby Dalbergia melanoxylon, although not of sufficient size to make an ensemble of clarinets (just piano keys!), and Acacia borleae with its sticky young growth, wavy-edged curved pods and glandular leaflets. Many of the grasses were annuals such as Enneapogon, Aristida, Urochloa and Setaria. There were a number of leguminous herbs, but we were too late in the season to see any evidence of the bulbous species often found in this habitat type. No Acacia tenuispina though (which would have been another first record for Zim) and no other specialized acacias other than the fairly widespread lowveld A. borleae.

Mark collected a Compositae herb which has been determined by Bob as Launaea intybacea. There is no record of this species for Zimbabwe in either the National Herbarium or in Flora Zambesiaca and it therefore appears to be a new record for Zimbabwe.

So, not quite the habitat we had originally envisaged, but none-the-less interesting, and a change from the surrounding mopane on gneiss and gravelly/stony soils. Perhaps with more time, and an opportunity to climb the geologically fascinating and diverse Marungudzi hill, we would find a lot more of interest.

Jonathan Timberlake

Thursday, April 20, continued:

We then travelled further, along the surprisingly good road to Chiturapadzi. The great interest here is the annual herb Triceratella drummondii, found new to science by Bob Drummond in 1958. An attempt was made in February 1997 in the company of Bob Faden, the expert on Commelinaceae, to re-find this, see Tree Life 205, March 1997, but this was unsuccessful.

Since then, a single plant of Triceratella has been found by a botanist doing an Environmental Impact Assessment at a mining site near the coast in Mozambique. Unfortunately, only a single plant was grabbed; no-one was aware until later of its significance and there was no chance to get the species into cultivation in order to count its chromosomes and examine its DNA.

Once again, we were not successful in finding the Triceratella, but Chiturapadzi is a wonderful site botanically anyway and this year a lot of water was seeping out of the hillside near the base creating a rich habitat of seepage zones and small ponds, filled with sedges and other annual herbs.

Three of these were of great interest to me: Exacum oldenlandioides, a small herb in the Gentian family with opposite leaves and blue flowers; Bacopa floribunda, a small Scroph. with white and brown flowers and Portulaca kermesina, a succulent with reddish flowers. Maureen also found a striking climbing Cucurbitaceae, Cucumis myriocarpus, which has spherical fruits with brown and white stripes. In the woody flora, a specimen of Grewia hexamita was found together with an unknown Vitex.

Our journey home was made shorter by taking farm tracks. Some interesting jog-stops (stops at which plant people browse and the rest of us jog on up the road to be collected as and when the others come on in the car) on the way resulted in us finding Rhigozum zambesiacum. Unfortunately the specimen was lost and we needed to devote part of a later day to re-finding it.

Mark and Linda Hyde

Friday, April 21

A local day, spent labelling trees around the camp in the morning. The banks of the Bubi show considerable damage with many large fallen trees and much mess caused by piled up branches and shrubs. The ground in the riverine vegetation was generally bare but was quickly recovering and various annual herbs (such as Argemone mexicana, Blumea viscosa and Datura innoxia) were beginning to appear.

The riverine forest consisted of: enormous Acacia galpinii, A. nigrescens, A. schweinfurthii, A. xanthophloea, Berchemia discolor, Combretum imberbe, C. mossambicense, Commiphora glandulosa, Croton megalobotrys, very large Diospyros mespiliformis, Faidherbia albida, Ficus sycomorus, Grewia bicolor, G. flavescens var. flavescens, Philenoptera violacea, Spirostachys africana. The large woody climber Cocculus hirsutus was also frequent.

In the afternoon we were offered a trip along the river with "Tokkie" Van der Merwe in the back of his open land rover. It was a road that wound through Mopane, acacia and thick riverine woodland which the floods had covered. Tokkie needed to check the road out before well healed American tourists arrived for the hunting season. One incongruous item of debris was a plastic dustbin (40-gallon size) which had landed the right way up in the middle of the road and subsequently filled with rainwater.

The skies darkened as we headed for home. Rain in the southern lowveld is very different from the warm Zambezi Valley; it is COLD. Clad only in shorts and shirts on the back of an open land rover we pulled our hats well down to protect eyes and cheeks, not from acacia branches but from the hail like rain. The half hour race back over the now slippery black mud was a dramatic contrast to the idyllic earlier part of the day. Shivering we stripped off before entering the room-with-a-view where, wrapped in towels, we waited in line for 2 minutes in the hot shower by candle light. That evening we all wore 2 layers of clothing plus jackets, not something you expect in the lowveld even in April.

Mark and Linda Hyde

Saturday April 22

The following day Mark braved the mud causeway back to the main road, although for at least half of this stretch the car edged crab-wise towards its destination. We found that diesel had been delivered to the main road garage overnight so the trip to the Mateke Hills was ON. North this time and then eastwards towards a granite plateau rising some 300 feet above the flat lowveld plains. Unfortunately we took a wrong turning and ended up running northwards along the edge instead of plunging into the middle of the hills. The road was very wet and the problem was compounded by the fact that it was also used as a cattle track. We finally balked at trying to cross a cattle pen with a fence on one side and thick mud (probably thixotropic) on the other and no sign of roads onto the plateau.

A lunch stop was followed by a scramble through some of the worst Aristida and Burr fields I have seen and the tantalising view from the top confirmed the "real" hills were still to the east. On the way back we stopped at a small outlier kopje close to the Sheba Ranch homestead - mostly rock and scrambling creepers with trees of various sizes poking through the granite (we had passed it 3 hours before and ignored it). Here, stamping hard on the rock to scare away snakes, we scrambled again to the top. This time we were rewarded with interesting plants (a small pavetta - possibly Pavetta incana, also recorded from Marungudzi; the wild cotton - Gossypium herbaceum, var. africanum and a species of Barleria (affinis), covered in stellate hairs). From the top, we had a 360 degree view of the hills to the north and the plains stretching south to the Bubi and beyond.

This time we were headed home in the twilight and the dark and were rewarded by the sight of giraffe, caught in our headlights on the road, followed by an enormous spider web which had been spun in the last 12 hours and spanned the road to a height of 12 feet. Unfortunately we had to break it to get to camp but I am sure that a more successful web would be spun in the bush the next day.

Linda Hyde

Easter Sunday, April 23

The day started very leisurely, everyone doing their own thing. Midmorning some of us took a drive along a gravel road to look for a particular shrub we had seen several evenings ago from a previous drive. We drove 3 or 4 kilometres, and then did some walking. Maureen was strolling with me, so helped me identify most of what we saw.

Two very striking "morning-glories" climbing on the shrubby vegetation were collected. One had pale yellow flowers with a dark centre which was determined by Bob as Merremia kentrocaulos var. pinnatifida; the other had smaller purple flowers and was Ipomoea magnusiana.

At last we spotted the mystery shrub, Rhigozum zambesiacum, Mopane Pomegranate, it has lovely golden yellow flowers.

Rose Greig

In the afternoon, some of us took the Landcruiser and drove following Tokkie's instructions along a fence line and up to a small hill with a Baobab on it. On the way, we stopped in a grove of Rhigozum zambesiacum. This is a distinctive species with small pinnate leaves each with tiny pinnae. An interesting spot-character for this species which I had not realised before was that the rhachis is winged. The same site saw further material of Acacia grandicornuta. Jonathan explained that this is usually a riverine species but here it was clearly not. To me it looked a bit like Acacia karroo (Jonathan mentioned the interesting fact that A. karroo rarely occurs at such low altitudes - hardly ever below 800m and here we were at c. 500m) but in any case the pods are different - those of grandicornuta resemble those of robusta or young gerrardii.

At our last stop, we found a shrubby Croton, which looked distinctly different to C. gratissimus and indeed it turned out to be C. pseudopulchellus.

The next day (Easter Monday, 24th) we left at the crack of dawn for an uneventful drive back to Harare.

Tailpiece and thanks

My great thanks to Tokkie and Rinie for being such marvellous hosts for the 5 days and for encouraging us to come, for providing help and advice and for lending us a GPS. Our thanks also go to Jonathan for shedding so much ecological and geological insight into what we saw and to Andy for organising the trip. Thanks also to Bob Drummond for naming nearly everything we collected. A complete list of the plants collected is available from me on a spreadsheet if anyone is interested.

Mark Hyde


Copyright: Mark Hyde, Bart Wursten, Petra Ballings and Meg Coates Palgrave, 2002-17

Hyde, M.A., Wursten, B.T., Ballings, P. & Coates Palgrave, M. (2017). Flora of Zimbabwe: Expedition no. 5: Tree Society outing to the Bubi River.
http://www.zimbabweflora.co.zw/speciesdata/outing-display.php?outing_id=5, retrieved 26 March 2017

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