Subs for the year 1996/97 were due on 1st April.
Tuesday 2nd April. Botanic Garden Walk at 4.45 for 5 p.m. We will meet Tom in the public car park of the Gardens and continue where we left off in February. There will be a guard for the cars.
Saturday 20th April. Note change of date. Mark’s Walk will be in the Greystone Park Nature Reserve. meet at 2.30 p.m
Sunday 21st April. The countryside to the northeast of Harare is looking so good after the rains that we thought a trip in that direction would be enjoyed. We meet at 9.30 a.m.
Tuesday 7th May. Botanic Garden Walk.
Sunday 19th May. NOTICE OF ANNUAL GENERAL MEETING. Notice is hereby given that the 46th Annual General Meeting of the Tree Society of Zimbabwe will be held on Sunday 19th May, 1996 at Mhowani Hills Farm, Teviotdale.
1. Notice convening the meeting.
3. Minutes of the 45th AGM.
4. Matters arising.
5. Chairman’s Report.
6. Treasurer’s Report.
7. Election of Committee Members.
8. Any Other Business.
Any proposals/resolutions and nominations for office bearers should be forwarded to P 0 Box 2128, Harare by Monday 13th May if possible, although proposals and nominations will be accepted from the floor.
GUITINGWOOD: 18TH MARCH, 1996.
John’s invitation which started with “my Water lilies are flowering and I’d like you to see them” was accepted with glee knowing that an interesting day would be ahead and also nearly three years have passed since the society enjoyed the superb wooded kopjie and Cottrill hospitality.
On our last visit we noticed the Wild basil, Ocimum sp. which when squeezed produces an odour similar to that of camphor crème, what we didn’t notice were the vicious prickles on the attractive Pink-flowered African foxglove, Ceratotheca triloba, tangled up in this mass of herbaceous plants. Something we don’t often see and which occurs in areas of previous ancient habitation, the star leaved Jatropha curcas or Physic Nut where the nut oil has a traditional use as an embrocation and for our energy hungry society, a diesel fuel substitute. Ziziphus mauritiana, very similar to its widespread relative Ziziphus mucronata but with an almost white leaf underside, with the fruits being a well known additive for Kachasu and, according to Food Plants of Zimbabwe, also used for treating children with convulsions in the Bindura area. Another food plant was Psydrax livida, a spreading tree rather than the small green shrub usually seen, with quantities of unripe fruits, generally only the leaves are edible. Being Rubiaceae don’t forget the inter-stipules!
A shallow hole nearby, evidently an iron smelting site containing a broken piece of a tuyere and various pieces of fissured slag scattered about as evidence, must have been a busy place many years ago, however, time had returned this place to its natural beauty. In the rocks above a bright glossy green Dovyalis zeyheri had been visited by a troop of Vervet monkeys earlier in the week and only a few of the small orange fruits remained and the discarded seeds found their way into packets. The other trees in this spot included a woodland Mahogany, Turraea nilotica with distinctive wavy edges to its leaves (remember the drawstring effect), Diospyros mespiliformis squeezing its way between rocks and the bright green paperbark Commiphora marlothii whose fruits are edible when ripe. Skirting the thickly wooded kopjie we had a look at Combretum adenogonium with the characteristic feature – whorls of leaves in threes and carefully snuggled into the crevice above a resident barn owl with its pale face turned towards the approaching noise, blinking occasionally at the rabble below.
Some helpful suggestions from Phil to key out the Clerodendrum genus are:
1) Clerodendrum glabrum has leaves in three’s
2) Clerodendrum wildii has pink/purple petioles and
3) Clerodendrum myricoides has more serrated crenate leaves.
So then the foetid smelling plant with pink petioles should be Clerodendrum wildii.
John’s finest tree is a wonderful spreading Sterculia quinqueloba with the huge forked trunk a patchwork of pinks and cream. Phil and I linked hands and ‘hugged’ the enormous bole – 2 Meg units plus 5 inches by eye. Once again Meg Coates Palgrave’s quick measurement provided an on the spot answer. The change in soil types from vlei to the loam around the kopjie, marked in places by a tumble of rocks, contained a variety of figs. From a small Ficus natalensis with its typically squared-off end to the leaf. Ficus sur with hard spherical fruits on short stalks to a great spread of Ficus glumosa, (I’m sure I heard Carolyn Dennison say Ficus glaucoma!) with pale roots engulfing and steadily inching a boulder out of the way. This is one of the true rock-splitters with small red hairy figs and a few larvae within the fruit which probably improved the flavour as most indigenous figs are a bit short on taste. The fig wasps inhabit the ripening fruit initially by being deposited in the base of the flower. When the grubs mature the female wasps escape through an enlarged hole made by the male.
Leaving Cheryl and Ken to Tarzan tactics with a liana, we gathered round a mature Pappea capensis with its label describing the many and various aliments which can be treated by parts of the tree, including the seed oil which is used as a hair restorer. For some of us – hope at least. Other trees included a large lone Marula, Sclerocarya birrea, a possible relic of some previous habitation, an enormous sausage tree Kigelia africana with scars on the trunk from where the bark had been slashed in the past. And a Ficus natalensis, with roots resembling a major railway junction and which bore multiple root scars caused by the collection of the white latex, this being used by nursing mothers to increase lactation. Some of the planted trees enjoying the safety of their timber surrounds in the arboretum are Bauhinia tomentosa with an attractive yellow flower, the climber Bauhinia galpinii, identified by its piece of red string. A young Fernandoa magnifica with highly serrated leaves, several more young Marula to befriend the lone one, a cluster of Combretum mossambicense and the others – Tamarindus indica, Entandrophragma caudatum and Craibia brevicaudata.
After lunch and a look at the Water lilies Nymphaea with John mentioning that the cultivars growing in the shallow ponds fit into three categories. Ranging from the tropical type where the flower is produced in a long peduncle above the water line such as the blue flowering indigenous Nymphaea caerulea, night flowering which are characterised by a deeper colour to both leaves and bloom with the remains of a spectacular deep red flower still visible on one plant and those from colder climates with a flower produced on the water line are termed as being hardy. Some of the cultivars included Panama Pacific with almost purple sepals, lilac flowers and the centre a mass of purple stamens and a pink flowering species named General Pershing. Water lilies are tidy plants for as soon as the flower starts to wither it slips below the water where the seeds mature and when the capsule bursts they are released and float on the water surface, eventually dropping into the mud below to germinate. The stems to the leaves are curious being slightly flattened and having what appeared to be three vein-like cores from leaf to roots. One of the other aquatic plants seen in a pond next to Lilian’s studio with very attractive three-petalled yellow flower is the water poppy, Hydrocleys nymphoides.
Once again many thanks indeed to John and Lilian for a most enjoyable day at Guitingwood.
TREE SOCIETY TRIP – RIFA HUNTERS’ CAMP CHIRUNDU – 29TH FEB. TO 3RD MARCH 1996.
THE ZAMBEZI FLOOD PLAIN
Thursday evening’s walk across the floodplain to the Zambezi crossing the dry sand bed of the Chipandaure River was through national parks and revealed an area of fascination in different ecological systems. A wealth of interactions and interdependence of trees, insects, grasses mammals and man emerged. Following the road from Rifa Camp to the Chipandaure was through trees, shrubs and open patches of grassland. The soil was red and very muddy. The sun had come out after a shower of rain and our attention was drawn to a myriad of butterflies and we were lucky to have with us two lepidopterists, Gareth Cornes and Marcus Jooste.
The Joker Byblia vatara was very common flying low on the open grassland preferring the longer grasses. The wings were dark orange with broad black terminal bands enclosing a series of orange spots. Various species of vigorously flying Colotis (family PIERIDAE) were seen gambolling with other species. A white Colotis with white wing and red tips was very evident. These were taking nectar from a Combretum.
Boscia is the food plant of the larval form. The next day a Zebra Pinacopteryx eriphia was seen rapidly depositing a single fluted egg on Boscia matabelensis. Laying was quick, if delayed the butterfly could have made a tasty meal. She was feeling with the tip of her abdomen for the rough hairs on the Boscia. The markings were extensive brown bands on an ocherous yellow background. The underside was darker which is a protective device because it lands on the ground when the sun goes behind a cloud and is rendered almost invisible. In the wet weather the marks are much darker.
The black tipped Acraea was abundant, low flying and gregarious. When at rest the wing is partly exposed and constantly opens and shuts. The Acraea have rounded wings and long abdomens. The black tipped Acraea is the orange poisonous Acraea caldarena. It releases cyanide from the base of the antenna when threatened and is poisonous to lizards and small birds alike.
The larval forms feed on Passiflora. The butterflies are often mimicked by other species as a protective mechanism. The milkweed butterflies are the monarch butterflies belonging to the DANAIDAE. Danaus chrysippus was seen in the evening feeding on an asclepiad. The butterfly has acrid poisonous juices derived from the food plant. They are unpalatable to birds and predators. If the larval forms are reared on cabbages these are non-toxic. The larval forms are so toxic that they do not bother to hide and are not camouflaged. Only the first instar is vulnerable. Danaus is a large butterfly with russet orange wings, black tips and white spots resembling an Acraea. Many other species mimic the monarch. The common grass yellow, Eurema hacabe was flitting everywhere. The larval food plant is grass. As dusk approached the brown heavy slow flying Evening Brown, Melantis leda (SATRYNIDAE) was seen indiscriminately dropping its eggs on the tall grasses – somehow it must have got the correct food species in its pepper pot attempt. There was no evidence it was seeking out a particular grass.
On the third day a rare Lepidochrysops glauca was caught. It had golden scales and was iridescent silvery blue. The last larval stage secretes a sugary substance and is taken in by ants that in return protect it in a form of symbiosis.
In full sun Combretum obovatum is visited by butterflies and other pollinators. The PAPILIONIDAE are strikingly beautiful large butterflies with swallow tails or sword tails. The flowers of Combretum obovatum are inconspicuous brown and white flowers. The leaves of the flowering branches have no chlorophyll and are white resembling petals to attract butterflies for pollination. The species is a dense bush with a five winged fruit. The multi-stemmed scrambling Combretum mossambicense has a purple stem, five-winged fruit and has white shaving brush flowers in the late dry season. It is pollinated by the swordtail butterfly Graphium species which inserts its proboscis into the bloom and pollinates by distributing pollen. Towards the evening when there is less turbulence odours are very distinctive. Capparis erythrocarpus, the mustard bush had hooked spines alongside each leaf and contains mustard oils. The mustard oils are an anti-browse mechanism. Citropsis daweana has the smell of orange when crushed and is called the wild citrus. It is attractive to Papilio demodocus the orange dog. Clerodendrum wildii has a repugnant smell when the leaves are bruised. Phyllanthus reticulatus was not in flower and did not give off a characteristic potato smell. Cleistochlamys kirkii the purple cluster pear has a striking odour due to the pellucid glands in the leaves. Moving away from bush and grassland more directly to the riverbed we passed under a Trichilia emetica (Natal Mahogany) we were shown leopard foot prints beneath the tree. Trichilia is a favourite resting place for leopards who lug their prey into a tree. The dense canopy prevents detection by vultures. Looking up into the dark dense canopy it could have been difficult to spot a leopard. As we passed through the riverbed the pug marks of a lioness and cubs were apparent and in the distance a male lion was grumbling. It was reassuring to have with us, two professional hunters and two armed game scouts who knew the area.
Passing along the buffalo tracks in the Adrenaline grass, Vetivaria, it was a relief not to stumble upon an old dagga boy. Combretum elaeagnoides, the large Jesse bush Combretum with leaves in whorls of three and scales on the stems was evident. Croton megalobotrys which grows along some tributaries of the Zambezi is dense because it is no longer grazed by rhino. The alluvial floodplain was crossed. The soil was fine and capped in places due to a salt content at the surface.
The grey ghostly almost leafless Faidherbia albida (formerly Acacia albida) the apple-ring acacia stood out like giants. The alluvial sand is water logged in the wet season and as a morphological adaptation, the tree drops its leaves to cut down the transpiration pull and is in a resting period. The flowers appear and then the leaves in winter followed by a profusion of apple-ring pods at the end of the dry season. Elephant not only survive on the protein rich apple-rings but eat the young trees grown from seeds or shoots from the root stock. One of the scouts had seen a small sapling destroyed by elephant in the dry season.
Erosion has exposed metres of root of one of these giants and shoots were seen developing a distance from the parent tree on the exposed roots. It is obvious the big giant will eventually fall a victim of erosion. The gully cut by the rain along the roots was at least 2m deep. The belief that these trees will become extinct because the plain is not flooded is a myth – the real problem is overgrazing and erosion. After the severe drought in the previous years when only half the average rainfall fell, overgrazing and cropping was apparent everywhere. Common on this alluvial terrace was Diospyros quiloensis, the crocodile bark tree was a favourite of rhino in the past. Dalbergia martinii the Zambezi Dalbergia were cropped right back.
Lonchocarpus capassa, the rain trees were browsed and stunted except for one very large towering tree. It was surrounded by numerous bush-like Lonchocarpus which could have grown from seedlings but might have sprouted from the rootstock. The Lonchocarpus is grazed by both elephant and antelope. The trees become infested with bugs called frog-hoppers, Ptyelus grossus during the late dry season. These little frog-hoppers suck up so much fluid that it is expressed like drops of rain and hence the name, Rain Tree. The tree has beautiful blue flowers.
The mopane, Colophospermum mopane enjoys poorly drained soil rich in sulphur. It has butterfly wing-like leaves that hang down in the heat of midday. An interesting adaptation is that when mopane are grazed, they release ethylene oxide which is carried downwind to other mopane trees. On picking up the ethylene oxide they are stimulated to produce terpenes which are anti-browse. Senna obtusifolia is disliked by hippos. Many of the acacias develop long thorns to prevent being grazed. These thorns are not so evident in the large trees.
There was one very large Acacia nigrescens (knob thorn) which had very large round leaflets for an acacia and big thorn bosses along the trunk. Acacia nigrescens is also being destroyed by elephants. The custodian of the Zambezi Valley is the tsetse fly Glossina species because it causes nagana in cattle. Man probably needs to be introduced to the area to stabilize the animal populations and to meld again as part of the environment.
The trees and plants of the area have many uses. A wild Dutchman’s Pipe, Aristolochia, was collected; an infusion of the roots is used for the treatment of malaria (National Parks Guide). The oval fruit of Balanites maughamii is soaked first in 200 litres and will kill bilharzia cercaria in the water. The fibrous seed is found in elephant dung. Balanites grows as a bush before sending out a long tall straight trunk. In the older trees these trunks are fluted.
The long sausages of Kigelia africana yield a cortisone compound used to initiate breast development in young girls. It should not be used for skin cancer because it is medically unproved and may not work when the growth is more deeply seated. The long pod of Cassia abbreviata is used for stomach pain. Trichilia emetica is an emetic.
Dugouts are hewn from the wooden banana, Entandrophragma caudatum, Lannea schweinfurthii (false Marula) and Cordyla africana (wild mango, mutondo) are made into fish traps. Fishing rods are made from the snowberry Flueggea virosa, purple cluster-pear Cleistochlamys kirkii and the northern dwaba-berry Friesodielsia obovata. Courbonia glauca is a fish poison.
Salvadora persica, the mustard tree was traditionally burnt; the ash soaked, decanted, evaporated and salts crystallised out and used to season meat. The main uses of the wild trees and plants by men seemed endless.
We arrived at the banks of the Zambezi River as the sun was setting. The sky was grey, blue and silver with touches of turquoise. Green colours in an evening sky mean the presence of moisture and more rain could be expected. The river was silvery grey blue as it slid past to be broken by the odd tree stump or surfacing snorting hippos.
Across the river, dusty grey-green Hyphaene petersiana palms stood with their crowns held high. Palms do not undergo secondary thickening in the trunks to produce more xylem vessels for transporting water. The crowns do not increase in size and for every new leaf an old leaf has to die. Palms grow taller but the crowns do not get bigger. The grass of the shore and deep blues of the distant hills stood out as a contrast against sky and river. A soothing peace was descending and the tranquillity of the approaching twilight can only be believed by those who have stood on the banks of the Great Zambezi and felt at one with the environment.
An early start and a walk to the sulphur spring with the alluvial flats covered with fine wavy heads of grass and everything so wonderfully green with patches of herbaceous plants containing an attractive yellow Hibiscus. The red flowers of Leonotis sp., exerted from the spiky brown balls and the lilac flowers of Cleome macrophylla. The larger trees dotted along the alluvial soils and base of the kopjie included Lonchocarpus bussei recognisable by having more pairs of leaflets than Lonchocarpus capassa but still having the same coarse texture. And an occasional Bird Plum, Berchemia zeyheri and along the stream the ripening reeds held several colonies of Red Bishops in full breeding plumage. In the overhanging rain trees Lonchocarpus capassa a small group of Brown Necked Parrots squawked in time to the Red-billed Hornbills melody from the kopjies. An unusual grey fungi sprouting up in a ring from a pile of old elephant dung had a little rolled up frilled edge, but oh how fragile as the slightest touch seemed to damage the membrane. A Gardenia volkensii had been heavily browsed but tucked in between bites a few tiny hemispherical nibbles showed it as being a food plant for a butterfly, the ‘red playboy’ – Deudorix sp. which is a dandy having bright red wings with a black edge and a grey underside.
Bubbling up through a fissure, the sulphurous water tossed the sand gently as it escaped. The high nutrient levels were encouraging some thick swathes of very green algae. Several clueless frogs met their doom having jumped in when disturbed and were now floating or lying limp. They appeared to be similar to the Leopard toad but as a result of being boiled the claws were pink. On virtually all the grass stems globules of foam hung down generally near a node, could this be a grasshopper nursery (?) and beside the stream in the seeding grass Sporobolus sp. we found an interesting cricket with a purple back and equipped with a powerful set of legs as well as ejecting an unpleasant liquid. Just before the kopjie an enormous creeper of the Mustard plant Salvadora persica using a similarly large Acacia nigrescens for support had in its folds an unusual Cucurbit – Coccinea sp. with small sausage shaped fruit with an orange end – something a little unusual.
The kopie climb is surprisingly steep, fortunately the cool morn kept the flies at bay and also the butterflies to the disappointment of the Butterfly Okes who had to wait until later for results. A big advantage to plants – they don’t need a temperature of 20 degrees plus to start up. A patch of the kopje could be termed a bit of ‘Jesse bush for beginners’. The site contained a number of typical species such as Commiphora karibensis with the really fluted dark grey trunk, Lannea schweinfurthii and Combretum celastroides with rampant shoots resulting from the first good rains in many years. This Combretum has small pale 4- to 5-winged fruits and broad opposite leaves with scales whereas Meiostemon tetrandrus (false Combretum) has smooth narrow shiny leaves and a flower with 4 stamens. The hilltop contained other species such as Entandrophragma caudatum, wooden banana, one of the few really big trees in this spot with a patchy bark, the unusual Strychnos decussata which has a very long attenuate tip to the dark green glossy leaves. A well-chewed Cordia pilosissima and a large pair of stiff rounded leaves produced from a really powerful climber doing some crazy turns identified the python creeper, Fockea multiflora, this is one of the few times we’ve seen it so covered in foliage. The Euphorbia awkwardly blocking the path in places appeared to have a small candelabra on a short stem with each having both four and five lobes, could it be one of the subspecies of Euphorbia cooperi? A relative by nature of its flower is Croton longipedicellatus, take a careful look at the leaves to confirm the two tiny glands at the junction of leaf blade and stalk. The leaves when crushed are aromatic producing a thyme-like odour. Also in this rocky kopie and identified as the leaves are rough and have scales underneath is Croton menyhartii, but without fruit. A Rubiaceae very like the usual Canthium lactescens but with smaller leaves and a well defined drip tip caused much discussion (Later confirmed by Bob Drummond as Canthium pseudorandii, the old name being Canthium burtii and in its correct habitat too).
While others went ‘butter-flying’ we had a look at the trees around the river and some of the features noted included Commiphora caerulea with a clear to brown sap and setting to a pale brown hard resin which is sour to the taste. The leaf of Karomia tettensis, wild Chinese Hats, has a distinct curve and a few deep serrations at the end with small pale pink flowers shaped not surprisingly like a tiny Chinese hats. Strophanthus kombe is often a spreading bush with large quilted leaves that are covered with stellate hairs, the fruits paired like some animal horns typical of the Apocynaceae. Clusters of red flat fruit sharing the spur like shoots with the dark leaves on Terminalia prunioides, Boscia mossambicensis has smooth leaves which we found out on the last visit. And large well-boled specimens of Cordyla africana (mtondo) are used for canoes as it is relatively easy to work and can be locally common in the alluvial soils.
An afternoon downpour and a really good soaking with warm rain. Rob, Alec and I having lost contact with the main group tried in vain to track with each spot of rain obliterating any spoor and the rivulets quickly spilling into the river (pronounced Chipandaure). The red sandstone banks slumped into the river during the wet part of January taking with them the nesting site of the Bee-eaters, fortunately not at home and exposed a seam of washed pebbles – could this be an indicator of an ancient watercourse or inland sea? A strong smell of buffalo filled the air – the thickets of Combretum obovatum with white terminal leaflets and Combretum mossambicense are a known lair of the lions, so we didn’t hang around looking for trouble. We caught up with a drenched but cheerful Tree Society only a km or so from the camp.
After tea and a change of clothes, Alec suggested a walk along the floodplain. Only a few hardy souls ventured out and what a fantastic walk it turned out to be. The skies and clouds turning to a glorious red, purple and finally gold with the Zambian escarpment a rampart of black mountains, and closer the silhouettes of the leafless albida with a lone elephant having a quick feed before sundown. Slipping up a really slippery bank the cries of anguish and giggling from those who fell into the mud were silenced by the guttural rumbling of the lions a few km away – a stirring sound and so well timed.
It had stopped raining, and we set off at 6.30 a.m. At first we walked through the Colophospermum mopane woodland behind the camp, but soon we were negotiating a narrow, muddy, slippery path that snaked up a hillside (through Acacia ataxacantha and Combretum elaeagnoides) and then contoured along the ridge. The vegetation was wonderfully green and lush. The beautiful, big trees included Afzelia quanzensis, Sterculia africana, Kirkia acuminata Xeroderris stuhlmannii, Commiphora caerulea with its unusual bluish underbark, and Commiphora karibensis with its characteristic fluted trunk. Carphalia pubescens was simultaneously displaying its white, scented flowers and fascinating ‘cups and saucers’ fruits. Karomia tettensis was also producing fruits, with their ‘Chinese hat’ shape. Terminalia prunioides was much in evidence. It was interesting to encounter unfamiliar species of familiar genera, including Lannea schweinfurthii, Lonchocarpus bussei, Pterocarpus lucens, and the yellow-flowered Bauhinia tomentosa.
On our return through the mopane woodland, it was a pleasure to see several pans that were brim-full of water, with weaver birds’ nests in the overhanging mopane branches. The water surface of almost all the pans was completely covered by a green, Lemma-like floating aquatic, except for one pan where water lilies were dominant.
After breakfast, we went in some of the vehicles as far as possible along a road towards the Chipandaure River, to a region upstream of the part we had visited yesterday. We struck off through the bush. Here, again, several species were fruiting. These included Allophylus africanus with its red berries, Friesodielsia obovata with its cluster of ‘crazy peanut’ fruits, and Strophanthus kombe with its pairs of long, cylindrical, curved pods, looking like an animal’s horns. Also present were Strychnos spinosa, Cleistochlamys kirkii, and numerous Diospyros quiloensis.
Then, the tall riverine trees came into view. We scrambled down the steep river bank beside a thicket of Combretum obovatum, with its white, petal-like leaves on the flower-beating branchlets. We strolled along the riverbed. It is usually dry and sandy, but now it had a thin surface layer of slippery mud, and there were even some pools of water. The large, shady trees on the banks included Tamarindus indica, Cordyla africana, Balanites maughamii and Commiphora caerulea. The smaller trees and shrubs included Diospyros senensis and Hippocratea parvifolia with its paddle-shaped pods. After returning to camp for lunch and a siesta, we set out towards the Zambezi on our afternoon walk. We passed through the Vetivaria grass and traversed the floodplain. Impala and waterbuck were grazing under the trees. At first, the dominant trees were Lonchocarpus capassa, with occasional specimens of Acacia nigrescens and Acacia tortilis. Then we entered Faidherbia albida country. Most of these trees were bare and leafless, but some were already producing their new leaves and were covered with cylindrical, white inflorescences. Finally, we reached the river bank, with its beautiful, big Trichilia emetica trees.
Shrubs that we encountered included Maytenus senegalensis, Senna singueana, Phyllanthus reticulatus known for its potato smell, and Flueggea virosa, which was particularly abundant along the river bank.
We walked along the bank to our meeting-place with the vehicles that had brought down our sundowner requirements. The sky was overcast, and we did not have a spectacular sunset this time. But the Zambezi was smooth and silver, with its mirror-like surface intermittently broken by surfacing hippos. In front of us, in the middle of the river, there was a sandbank on which rested an enormous crocodile accompanied by a yellow-billed stork and several Egyptian geese. We sat and watched, and it was a perfect end to a most enjoyable day.
The wet season and so different to our last look at the old pilot scheme for the Sugar Estates now swathed in grasses and annuals including the pretty yellow flowering Crotalaria sp. and a lilac Ipomoea sp. Even the viciously barbed green thickets of Acacia ataxacantha seemed far less hostile with elephant paths criss-crossing and a feature not experienced before, the thickets exclude almost all cooling draughts and it became really humid while meandering (slowly) through them. As we learnt later from the hunters, these thickets are liked by elephant cows with calves. On route to Long Pan through stands of Mopane the frequency of muddy soaks and small pans increasing until a broad sheet of brown water appeared through the woodland ahead above the multitudes of fruiting grasses. One of these resembled a 3-bladed helicopter rotor, this being Dactyloctenium giganteum. Around the pan a variety of really large trees such as Xanthocercis zambesiaca, a few Diospyros quiloensis and one particularly large fruiting Berchemia zeyheri with broken bits of foliage and sticky seeds spread below by the recent orgy of feeding baboons, our approach had probably disturbed them.
A quick march back to camp with a final look at the elephant playground of flattened grasses, the tiny nurseries of grasses and annuals established within the branches of the few collapsed trees and the spoor of an adult lion and two cubs in the damp sand of the river.
A really fantastic few days and so wonderful to see the Zambezi Valley so green and wet.
Many thanks to Meryl and Margaret for catering, Alec, Rob and Hugh for being ‘protectors’ and to the Parks scouts Derrison and Ignatious. A very big thank you to Leslee Maasdorp for organising the camp for us and to Bob for ensuring that we were fed and for transporting the mountains of food which we devoured, and to Maureen for putting the trip together. A new slant to our botanising has started with thanks to the Lepidopterists, Marcus and Gareth.
PS. The area around the camp site at Marongora is well worth a visit.
CHESA FOREST RESEARCH STATION, BULAWAYO. 3rd MARCH 1996
One of Bulawayo’s quieter spots, near its highest point of 1465m, on a fine day was the venue for March’s Matabeleland visit. Just outside the city’s boundaries there is a relatively small cap of ‘Kalahari’ (or similar) sand, underlain by a fair amount of calcrete, sitting on top of the more normal metasediments and metavolcanics which characterise so much of Bulawayo. It is here that the Forestry Commission set up a Forestry Research Station in 1985 to cater for the drier parts of the country. The original site, at Chesa Forest (hence the rather inappropriate name as the Research Station is actually on Matopos Trust land next to Criterion Waterworks!) is some 40km NW of Bulawayo, but was rather unsafe at the time. We looked at some of the Forestry activities, such as the nursery with a selection of provenances of Acacia karroo almost ready for planting out. The 10 year old trial of many provenances of Faidherbia albida from all over Africa, some of them already in leaf yet others still stark bare thus showing the range of variability and growth rates. And the 11 year old plantations of the attractive Eucalyptus citriodora among other gums. Then the small group sauntered off and strung out at a slow pace looking at the various trees and shrubs of the sands.
Most notable were scattered, large spreading almost flat-topped trees of Acacia sieberiana, along with the occasional clump of vegetation, probably associated with old termitaria, containing Euphorbia ingens and a diversity of shrubs, including Carissa edulis. Away from the clumps the differences between Albizia amara and Peltophorum africanum – shape, habit and the rusty-red buds of the latter – were seen clearly. Albizia and Terminalia species were prominent, especially Albizia amara, Terminalia sericea and what was possibly Terminalia trichopoda or Terminalia stenostachya. Among the more widespread acacias were Acacia nilotica and Acacia rehmanniana. A very peaceful location this and much bird life, including an array of bee-eaters on the overhead power lines.
This year’s crop of wild fruits promises to be good. The fruits we saw included Flacourtia indica, Strychnos spinosa, and some large trees of Sclerocarya birrea, Ziziphus mucronata, Dovyalis zeyheri, Carissa edulis and Azanza garckeana, mostly on the sandier soils. Strange how wild fruits are principally confined to the lighter textured soils and alluvium across the country.
After about half a kilometre we noticed a change in vegetation structure and species as we moved off the sand and on to gravels and clays derived from metasediments, part of the same formation as Tshabalala and portions of Matopos Research Station. Acacia were dominant here, with Acacia nilotica, Acacia gerrardii, Acacia robusta ssp. robusta, Acacia karroo, and the ubiquitous Dichrostachys cinerea.
The vegetation is essentially an Acacia bushland or low woodland. The saunter culminated in a perambulation around a lovely flooded gravel pit while Timberlake junior looked at baby bullfrogs. Both Euclea species were here, Euclea divinorum and Euclea crispa. And there was a delightful little solitary mauve flowering Mundulea sericea. The total species count was 50.
Our thanks to Mr. Dzidzai Maruzane of the Research and Development Division of the Forestry Commission for permission to visit the Station.
CONIFERS, WITH LYN MULLIN: 5 MARCH 1996
With Tom out of the country, Lyn Mullin took over at short notice to talk about conifers. The location was moved to the Forestry Commission Headquarters off Orange Grove Drive, in Highlands. The main subject was Gymnosperms and in particular, the subgroup of conifers (Pinopsida). Gymnosperms have ‘naked seeds’; they are generally monoecious (male and female flowers in separate places on the same tree), generally woody and mostly wind-pollinated.
In the conifers there are 7 families, of which 4 are represented at the Forestry Commission. These were: Araucariaceae, Cupressaceae, Taxodiaceae and Pinaceae.
Firstly we looked at the Araucariaceae. There are three genera worldwide, with 2 planted here. Agathis australis, the Kauri Pine, from New Zealand, which likes wet subtropical conditions, has been planted in the Imbeza Valley. It is a tall tree, producing high-quality timber. Surprisingly one specimen was producing milky latex from the cut leaves.
On to Araucaria. Lyn mentioned that this is a Gondwanaland genus, occurring in Australia and S. America. Lyn described the three groups into which the species are classified and we saw examples of each Broad leaves: Araucaria bidwillii; awl-shaped: Araucaria columnaris and with awl-shaped juvenile and broad mature leaves: Araucaria hunsteinii.
In the family Cupressaceae, Lyn distinguished between Cupressus (leaves not or scarcely flattened) and Chamaecyparis (leaves flattened). However, the distinction is difficult and an inter-generic hybrid (x Cupressocyparis) exists.
In rapidly darkening conditions, we reached the Pinaceae. In Pinus, there are 3 subgenera: Ducampopinus (only Pinus kaempferi); Strobus, the Soft Pines with a single vascular bundle; Pinus, the Hard Pines with 2 vascular bundles. There was hardly time to more than glance at Cunninghamia in the Taxodiaceae.
Space forbids giving all the details of this fascinating talk and it was suggested that it could be held again at a later stage, perhaps in an afternoon.
One final point. The Tree Society mostly looks at indigenous trees and indeed rather frowns upon planted or exotic trees, perhaps because we mostly encounter species like Guava, Jacaranda and Melia azedarach, which are invading and displacing the indigenous vegetation. However a talk like this shows what interest there is to be found in our park and gardens and I, for one, would welcome more attention to this subject.
Our very great thanks go to Lyn for a fascinating walk.
HOW TREES TRIED TO KILL OFF LIFE ON EARTH BUT GAVE MANKIND A VITAL CHANCE TO THRIVE. EXTINCTION
Invasion of the conifers was the first link in our long evolutionary chain.
Tall evergreen trees, generally viewed as benevolent predators against winter avalanches in the mountains and an agreeable part of nature, were once ‘killers’ –responsible for repeated mass extinctions that wiped out most life on the planet.
This happened during the Devonian period – named after the unique character of fossils and rocks first found in what is now Devon and Cornwall – that lasted between 400 million and 350 million years ago. The history of Earth is filled with mass extinctions, when all or most animals suddenly vanished. The best known of these is the destruction of the dinosaurs by the impact of a giant asteroid or comet 65 million years ago.
But there were many earlier ones hitherto wrapped in mystery which do not seem to have had any such violent cause. It is almost as if a giant invisible hand had descended from the skies or risen from the depths and extinguished our primordial ancestors, leaving behind no clue to its nature.
The Devonian period came long before the reign of the dinosaurs which were not to appear for another 100 million years. But the great ‘radiation explosion’ of life of the Cambrian period 500 million years ago had filled the seas with coral and a vast profusion of other primitive marine creatures.
The world was very different from today. The Moon was closer than it is now, making the Earth rotate so fast that days lasted about 21 hours, with each year thus lasting about 400 days – a fact that significantly increased the rate of land erosion.
Europe and North America had collided. The consequent up-thrust of mountains, which were also expanded by frequent volcanic eruptions, caused a great swelling of ocean waters that covered 85 per cent of the planet, compared with only 70 per cent today. The cause of the Devonian ‘crisis’, which according to the latest New Scientist recurred eight times, was the evolution on land of tall evergreen trees, the first ancestors of today’s pines, spruces, firs and larches. They proliferated on the shores of the huge oceans and above the banks of the rivers that flowed into them. “The trouble came when they evolved from small creeping plants to tall trees” said Prof. Thomas Algeo, a geochemist at the University of Cincinnati in Ohio.
“Their roots spread deeply and colonised previously barren areas. They did not have the stabilising influence on the soil that tree roots do today. The more deeply the roots delved into the ground, the more they broke up the surface and its rocks, making the soil more vulnerable to weathering and erosion.” Rainfall brought innumerable landslides. Soil particles and dissolved nutrients poured down the hillsides, washing into the rivers and oceans, where they caused an explosive growth of marine algae and bacteria.
When these organisms died, their decomposition used up the oxygen in the deeper oceans and the marine animals literally suffocated. This theory fits well with all that is known about the evolution and spread of primordial conifer trees.
Each extinction was followed by a population explosion of trees which led to the next extinction. Prof. Algeo also points to black shale rocks, which were formed during the Devonian epoch and which are filled with algal material.
But were these and later mass extinctions a disaster or a blessing? Did they delay or advance the coming of intelligent life? Prof. Algeo is convinced of the latter case. “Every time you have a mass extinction, it enables new life to spread, replacing the habitats of the old. The trees themselves which had caused the extinctions spread inland, causing more lush plant life to colonise the barren lands and appear all over the planet. This in turn created an environment in which large land animals could eventually exist.”
As for the much later extinction of the dinosaurs, that in turn made possible the coming of man, enabling our primate ancestors to fill the void they had vacated.
We have every reason to be grateful for the conifers that now fill Earth’s cold and mountainous regions with their melancholy beauty.
-Adrian Berry The Sunday Telegraph. Apr.’95.
SOME ORIGINS AND MEANINGS OF PLANT NAMES.
Extracted from W.P.U Jackson’s book.
Acacia (Fabaceae, Mimosoideae) From the Greek, akakia, the Egyptian thorn, probably from ake, a point; akanthos, a thorn.
Olax (Olacaceae) From the Doric, olax, a furrow, referring to the ridged bark. The Greek word was aulax.
Adansonia (Bombacaceae) Honouring the French surgeon-naturalist, Michel Adanson (1727-1806), who saw and described the baobab tree (Adansonia digitata) while travelling in Senegal around 1750.
Artabotrys (Annonaceae) Named by R. Brown, who writes that artana is Greek for “that by which something is hung up” and botrys “a cluster of grapes”. Referring to the “curious grapple or tendril” arising from the flower stalk of some members of the genus by which the “growing fruit is conveniently suspended on the nearest support during its advance to maturity”, thus transferring the increasing weight from its own slender branch. The name was used by Dioscorides for a herb “like wormwood”.
Becium (Lamiaceae) Ancient name for sage.
Brachylaena (Asteraceae) brachus, short; klaina, cloak; the involucre being shorter than the florets.
Clerodendrum (Verbenaceae) From the Greek kleros, chance or lot; dendron, tree. A “chancy” tree, perhaps alluding to its doubtful medicinal properties.
Mimosa (Mimosoideae) From the Greek mimos, to mimic. Apparently a Linnaean flight of fancy, the plants “imitating” animals; the leaves are sensitive to touch and “shrink” when handled.
KEY TO THE TREES OF ZIMBABWE By Meg Coates Palgrave.
Meg’s new book will be released at the end of April at a price of $215.00 per copy.
However, there is a special pre-publication price of $189.00 and so that members can take advantage of this considerable reduction in price we are enclosing an order form which we have obtained from Meg’s appointed sellers for you. You will be telephoned when your order is ready. We do advise those members who can, and especially Harare members, to collect their books from the sellers at 53 Ridgeway South Highlands Harare, which office is open from Monday to Friday 8.30 to 1.00 and 2.00 to 5.00 in order to save the registered postage charges. Please indicate under your telephone number that you will collect.
ANDY MACNAUGHTAN CHAIRMAN