March1999
No 229

JOURNAL OF THE
TREE SOCIETY OF ZIMBABWE
P.O BOX 2128
HARARE

MATABELELAND CALENDAR
Sunday 7 March. Probably to Chelmsford Park in the Waterford area. Meet at the car park in Girls' College at 8 for departure at 8.30 a.m. To confirm the venue phone Jonathan Timberlake on 46529, Tessa Ball on 46207 at home or Gill Short at home on 41541.
On a date still to be fixed Tom Raub has agreed to show some of his slides of plants which grow in his home state of Virginia USA.

WEEDS, WINGS, DAMSEL FLIES AND OTHER THINGS
The visit to Serui Source Norton was not just interesting from the trees but from the detailed inform¬ation given by Mark Hyde on the general vegetation and some of the insect species encountered.
The area was farmland with the usual granite outcrops and cleared lands. In the cleared grassland areas and under the trees were numerous exotic plants establishing themselves as weeds. A weed, in simple terms, is a wild herbaceous plant growing where it is not wanted and posing a threat to arable crops and grasslands or a garden nuisance.
These introductions establish themselves very success¬¬fully and the process of their colonization is on going in both our gardens and in farmland and undisturbed fallow areas. Once introduced and their hold is established weeds become a serious economic problem.
Gallant soldier or Galinsoga parviflora sometimes called quick weed or chickweed in Europe is originally from South America but is cosmopolitan. It is a soft small composite weed common to gardens, cultivated lands, roadsides and waste places.
In the grassland towards the dam were two varieties of Solanum; Solanum incanum is identified by its stellate hairs. The light green large toothed leaves with their pale furry beige green underside, star shaped blue to mauve flowers and characteristic round fruits are a common sight. The plant belongs to the deadly nightshade and is sometimes called a Sodom Apple. It is poisonous but the cut fruit has been reputed to be a traditional cure for ring-worm (an itchy fungal growth of the skin). It belongs to the Solanaceae as do crops such as potato, eggplant, tobacco and paprika. It is a nuisance to paprika growers because it harbours the same diseases and pests.
An attractive pink-flowered Cleome, erect, branched with fine long hairy leaves and spindle-like pods and is common in grassland and grain crops. The leaves of Cleome monophylla are edible and the seeds used as mustard. It is indigenous and has very long tap¬roots.
Conyza and Erigeron are the Fleabanes (America) and the species seen was Conyza ethiopica. The weed is found in fallow non¬cultivated lands and is not normally a problem to crops except under minimum tillage conditions.
Bidens pilosa the common broad leaf blackjack was introduced from tropical America into Southern Africa over a century ago. How often has it been necessary to pull the long three spined blackjack seeds from socks and clothing after walking in the bush? A five-leafed blackjack Bidens bipinnata has only recently started to manifest itself and is a new introduction. It is closely related to the five-leafed Bidens biternata. All three species occur in Zimbabwe together with the beautiful pink Cosmos or Bidens formosa spread by ladies throwing the seed from their carriages and now an export on the flower market.
Introduced too, is the Khaki weed (Tagetes), which was introduced in imported contaminated hay, used to feed the horses belonging to the “Kakies”, the British soldiers in the Boer war. It is beneficial as a rotation for nematode infested soils and even cultivated for its essential oils used in the perfume industry. Another Zimbabwean export from Marondera.
It all comes back to the definition. When is a weed not a weed and the answer is when it becomes beneficial. Very often the reverse is explained as a “garden escapee" for example Duranta, not to mention the Jacaranda, Jacaranda mimosifolia so beautiful lining the streets but now becoming a serious invader of indigenous woodland. How often has exotic Toona ciliata been confused with indigenous Ekebergia capensis?
On an anthill were a group of trees, Pterocarpus angolensis, Vitex payos, and Grewia flavescens. Underneath were some tall Psychotria shrubs shading an elegant carpet of grass. The grass was Setaria homonyma with broad leaves folded like a fan.
Gently resting and fluttering feebly when disturbed were numerous mature male and female damselflies. At rest their paired long narrow wings were held together over the slender segmented abdomen. Their wings do not allow for robust flight like their predatory relatives the dragonflies. Their bodies were dark brown with yellow stripes on the sides and a tiny triangle of yellow in the forewing. Unlike the antlions with which they could be confused they are not hairy. The two belong to completely different orders, the damselflies to the Odonata and the antlions – the Neuroptera family Myrmeleontidae.

Their life cycles are different and unusual though their appearances might be superficially similar. The antlion adult is more robust, hairy and has clubbed antennae. The wings are blotched black or brown and they hunt by night on the wing much like a dragonfly. The damselflies belong to the suborder Ephemeroptera, reflecting their ephemeral state. The delicate often metallic green, blue or azure adult only lives a few weeks and does not feed in the adult stage. Those seen under the bushes were a variety that does not cling to vegetation by the waters edge but hide away under bushes even on hilltops to escape predators in southern Africa the most common genus is Chlorestes. They mate in January/February making short flights over water. The male clasps the female behind the head with claspers at the tip of his abdomen. After an elaborate transfer of sperm from a special receptacle on the second abdominal segment the eggs are laid in the fleshy stem of a plant overhanging water. A slit is made and each egg deposited, up to six on a stem. The nymph hatches and lives in the water as a peculiar crawling creature with a huge mask held under its head. The mask is formed from the lower lip or labium and bears a pair of pincers. The dragon-like creature stalks its prey and shoots the mask forward seizing the prey in its mandibles. The tip of the abdomen has a pair of paddle-like tracheal gills. When the nymph is ready to do the final moult it climbs out the water on the stem of a plant, splits the nymphal skin and has no more use for the mask or gills. It has entered its most transient stage and has emerged a delicate and beautiful creature of the light.
The antlion larva is equally gross. Some species form characteristic conical pits and live at the bottom buried in the sand. When a hapless victim falls into the pit it is unable to climb the sandy walls and is brought down by the antlion flicking a barrage of sand. The mandibles, which seize the prey, form a tube with the maxillae and the juices are sucked out of the victim. The remains can be tossed out of the pit or a new pit constructed. In sandy soils wind and other disturb¬ances destroy the pits and these have to be regularly constructed and normally at night. The antlion has no mouth and no anus and the liquid diet wastes are processed by the equivalent of the insect kidneys called malpighiam tubes. Not all antlions dig pits but some larvae are free living in the soil where they burrow backwards forming ridges, tunnels and peculiar tracks when they are on the surface. The body makes the main furrow and the six legs dots on either side of it. Such activities normally take place under the cover of darkness. The antlion forms a pupal case covered in sand at the bottom of the pit. It emerges into a robust unattractive adult having four stages to the life history, egg, larval form, pupa and adult. It has a complete metamorphosis and is referred to as an Endopterygote insect. In simple terms it develops its wings in the pupal case. The damselfly has an incomplete metamorphosis and develops its wings and buds out growing from the nymphal exoskeleton, there is no pupal stage and it is an exopterygote insect.
Although the trees were good in different varieties the outing was distracted by weeds, wings and other things that sometimes enhance the pleasure.
How often has the appearance of a Jacaranda caused irritation not to mention the load of blackjacks carried home and perhaps time should be spent considering their ecological impact?
We thank James and Ann Sinclair for another really super outing on Serui Source.
MARY TOET

Not Enough Fire in Our Woodland?
As a schoolboy I was fortunate to spend holidays on a farm in the Lomagundi district where much of our time was spent horseback riding. The countryside was delightful – hilly with lightly wooded valleys through which we could canter freely. Today, fifty years on those valleys are so thickly wooded that it would be difficult to lead a horse through, let alone ride. What has led to this retrogression?
In Southern Africa there is strong ecological evidence that the natural succession of woodland vegetation is towards a climax of thicket formation and that bushfire is the principal factor that can inhibit this process into what Ecologists refer to as fire induced open woodland climax – parkland in fact. Trapnell's experiments of the 1950's conducted in strong Brachystegia woodland in Zambia showed this quite clearly. Annual burning in October, the so-called 'hot' burn, resulted in the classic open woodland with a vigorous grass cover. An annual burn earlier in the season – the 'cool' burn – resulted in more tree sapling and less grass growth whereas total protection against fire ended in thicket formation.
Talk of fire in our trees is sacrilege to many of our members and has no argument with them as far as the high rainfall forests in our eastern districts are concerned. The constituent species of those forests are extremely sensitive to fire and their distribution is governed very largely in that region by that factor. They must be protected from fire at all costs. But over the rest of the country Nature has ensured that many of our tree species are fire tolerant to withstand the effects of a passing fire. The bark of these species is usually thick and protective. Others tend to grow in places less prone to fire such as rocky outcrops.
The point is that periodic fire was a natural feature of the environment until farmers and ranchers took protective measures. At the turn of the century the early Settlers in this land found the countryside to be generally open woodland as induced by the periodic fires that had resulted from lightning strikes and the activities of hunters. Given the generally light stocking rate of game and domestic stock at that time, these fires, well fuelled by abundant grass, would burn on for weeks sweeping over large tracts of the land killing off many of the young tender tree saplings and so keeping the wooded areas in pristine open conditions.
One is faced with a drastically different picture today. Bush encroachment and thicket formation is a slow insidious phenomenon so that many are often not aware of the changes that have come about following the incessant overgrazing and successful protection against fire. But drive along any road through the countryside and you will see abundant evidence of these changes. The problem is most acute on red soil areas, less so on granite sand soils, while vleis, being waterlogged for much of the year, are not usually affected.
Dichrostachys cinerea with its pretty Chinese lantern flowers exemplifies the notorious encroachers. The leguminous pods of this bush are relished by herbi¬vores. The seeds being hard, are not digested, and the plant spreads rapidly especially on overgrazed areas to form ever-expanding impenetrable thickets. Being denuded of grass underneath, these thickets remain unharmed by any passing fire. Lantana camara, the ornamental introduced from tropical America, is a further example of a detrimental invader. In Matabeleland, Acacia nilotica has multiplied greatly degrading large tracts of grazing land while in the lowveld; Acacia nigrescens often forms thickets where fire has been eliminated.
In Mashonaland, Brachystegia spiciformis and Julbernardia globiflora commonly occur as copses of undersized trees especially where cut over in the past. Coppice growth (multiple stems) normally proliferated from the stumps of trees felled purposely as exhibited in the vicinity of early mines where local timber was used to for the steam boilers. More recently we see evidence of invasion by Jacaranda and Guava.
None of these would be a problem if there was sufficient grass to fuel a fierce fire and if the firebrands had their way. Where this process of invasion is allowed to prevail, the grasses become suppressed and offer less in the way of competition. Add in excessive grazing pressure and the competitive effect of the grasses is further reduced and so bush gains the upper hand.
Given that so much of our woodland is retrogressing in this way, the question arises as to the desirability, if any, of thickets and coppices. Economically, they have little value following the suppression of grazing while aesthetically, I for one much prefer to see a well grown specimen of a tree rather than one crowded and stunted in a thicket. Biologically, too, the habitat changes radically between open woodland and thicket; grazing animals give way to browsers and birds change. Thickets are fine for robins and perhaps shrikes but are totally unattractive to ground hornbills, storks and secretary birds by way of example. The clear visibility and freedom of movement in open woodland is perhaps its greatest attraction although it may be that the biodiversity in plants in unburnt wood¬land in the early phases of the succession process, at least, may be greater and so of more interest to the Botanist.
Given the high value placed on grazing today, the veld fire is no longer a significant management tool to control bush encroachment and woodland thickening. The worrying fact is that there are seemingly no acceptable alternatives. Grubbing the undesirable invaders out by hand is expensive and frequently new shoots proliferate from the fractured roots worsening the problem. Ring-barking can easily kill a large tree but not a bush. Arboricides are expensive and are seldom totally effective. In any event we have enough chemical pollution. Theoretically, intensive browsing by animals should suppress the bush and so favour the grasses but I have yet to see the method work reliably in practice. That would be the nicest way if we could get it to work.
Many years ago l was told by an eminent agricultural scientist that the easiest and most effective means of controlling bush encroachment in this country was to turn the land over to intensive settlement as occurs in our communal areas where the people will very quickly crop the excess wood for fuel and building materials. Unfortunately, the approach would tip the scales too far placing most other natural resources at risk.
The purpose of this note has been to defend fire from its wrongful reputation as the villain in range management. Outside of the montane rain forest where it is acknowledged that fire can wreak untold damage, the evidence points to fire having played a greatly beneficial role in the past in maintaining the open character of our woodlands and so promoting the grazing resource. Sadly, its use is now largely history and we are left with little promise of an acceptable alternative. This is of greater significance to those who depend on grazing resources for their living because bush intensification is synonymous with diminished grass availability. But for the tree lover there will be plenty to see in the foreseeable future even if we have to brave the thickets occasionally!
JHW

DEVULI 4 – 9 February 1999
After a month's wandering in the UK and just a few days to adjust, it did seem absurd to head off into the steamy lowveld at the height of the rains. Anyway Commiphora and Mopane are familiar species and I haven't yet developed a feel for Oak, Beech and Hawthorn.
Intending to travel in convoy with the Hydes lead to some confusion and after various stops en route to see if they would catch up, we headed through pouring rain to Birchenough Bridge and then to the ranch. To save face over the delay we pondered over this problem and decided to play a trick on the others using a piece of Mopane. This is where the plan fell flat – the pickup truck bogged down up to its axles in the soft treacherous soils. A tractor was eventually sought which provided the necessary pull under the bleak gaze of its single feeble headlight. Our arrival at the camp some 3 hours later was initially greeted with concern followed by much merriment as the story unfolded – the Hydes had been 20 minutes ahead. Anyway onto more important issues – the camp with its 3 comfortable A-frame lodges overlooks the wide sandy Sabi River at a point just upstream of Moodies Drift. Mount Rudd, a few km away to the east dominates this flat terrain with its red sandstone 'head' about 500 m above the surrounding countryside. The soils here are deep alluvium and support open woodland consisting of tall Acacia tortilis
Lonchocarpus capassa and Nyala berry Xanthocercis zambesiaca. The especially wet conditions have given the herbaceous plants a bumper year with Grewia, Ipomoea, Albizia anthelmintica and numerous Acalypha all tangled together with the rampant climbing Acacia schweinfurthii. A useful tip here for this Acacia – look for the elongated gland at the base of the leaf. With all these herbaceous delights at their prime meant Mark had a really good haul. One of the prostrate plants that seems to colonise paths and with an attractive yellow flower is none other than Tribulus terrestris – the Devil Thorn – there are fierce spines on the fruit, just another reason along with Scorpions to keep your shoes on.
A shallow ridge to the right of the alluvium provides another habitat – this being a mass of broken sand¬stones, with the thin soils providing a habitat for Baobab – so far free of sooty mould, Sterculia rogersii where the squat purple coloured bole appears to have little problem in displacing rock and an unusual one for us – Commiphora tenuipetiolata, conspicuous with green to blue underbark and the distinguishing feature of a long and slender petiole supporting a three foliate leaf.
Gyrocarpus americanus, the propeller tree is also common here and has an interesting lobed leaf – this is subsp. africanus, but other subspecies occur in Australia and in America. Perhaps Lyn Mullin could shed more light on this 'intercontinental' species?
Not surprisingly after a couple of hours tramping about in the humid conditions we found ourselves back in the camp eagerly grasping cool drinks, where a surprise greeted our arrival – a partly consumed carcass of a Whip Scorpion dropped onto the table. This is a strange creature – there are two long thin whips adjacent to the scorpion like claws and three pairs of legs while the coloration is similar to the common 'flattie' wall spider. It is supposed to be harmless and appears to be in the family Amblypygidae. Does anyone have any information on these creatures?
An afternoon walk along the riverine woodland and around stands of grasses, the most obvious being Dactyloctenium giganteum, this looks like a crows foot. The grass stands almost a meter in height and its specific name refers to the large limply hanging anthers. On the sandy roadside a group of Vervet monkeys were observed eating what seemed to be Guava's but a closer examination revealed the fruit of the climber Capparis tomentosa. Similar to a Guava at first, with pink pulp and numerous white seeds. Isobel tasted this delicacy from nature and found it to be slightly sweet; we carefully noted the time of consumption in case any strange medical conditions developed.
Another picturesque spot was the shallow hills close to the workshops but access required Mark to do some careful traversing over an eroded dam wall – less than a hand's width of clearance each side. In the hills the effort reaped results with both subspecies of Acacia senegal seen, this is exciting as the only other recourse we have had is the Bot. Garden. The two major differences are var. leiorhachis a distinctive tall spindly tree with a flaky yellow bark while the other var. rostrata is a small spreading tree distinctly grey in appearance. Our congratulations to Tom Muller as we remembered the 3 hooks. From the water tanks at the top of the largest hillock rain reduced the view of the surrounding countryside to a monochrome grey with the Sabi snaking its way about 2 km away. Other obvious trees in the vicinity were old favourites – Commiphora viminea – the Zebra bark, numerous Baobab, and Terminalia prunioides with swathes of purple fruits hanging in the damp air.
Another find was the stiff rounded succulent leaves of Salvadora persica, but the find of Salvadora australis which has leaves smaller than the above with a blue-green tinge was a new one for us. There is some reference to these plants having edible properties but quite frankly the especially foetid smell released by damaged leaves would put me off. This may be protection for the plant from browsers when conditions are dry.
A final wander took us along the river itself – the waters having subsided leaving the tangled remains of small trees, bushes and shrubs. On the less eroded sections typically thick lowveld riverine vegetation marks the river's course with large Trichilia emetica and bird plum Berchemia discolor forming the canopy, while some of the lesser known species such as Maclura africana which is from the Fig family yet has spine tipped branches, Azima tetracantha with spines neatly arranged at right angles, a climbing Dalbergia arbutifolia laden with flat green pods and an electrified Buffalo fence – beware of these when botanising.
Many thanks to Maureen for organising this really enjoyable trip which we found fell into two quarter degree squares, and thanks to those who obligingly continued to point out electric fences during our wanderings.
A. MacNaughtan

NYARUPINDA CATCHMENT 6 Feb.1999
The Scene. Wet.
Gentle rain on the whole, one windstorm, no hail yet. Rainfall October 2mm, November 99mm, December 163mm, 15 days without rain, January 384mm, only 5 days nil rain, February 71 mm, showers daily, total for season to date 6/2/99 – 719mm. Last season totalled 600mm. Sunless cloudy weather must be ideal for the Planarians, those flatworms on termite mound chimneys, but miserable for us, livestock and for our crops which also dislike wet feet. The swimming pool temperature is 25.5°C; the warmest was on Dec 19th 28°C. The Nyarupinda dam filled early in January; the river is opaque with silt and fast-flowing. The noxious floating water plant Azolla has been washed from the pool where it started and is now at the perimeter of the dam; much has gone over the spillway and on its way to the Susuji River 6km distant. Continuous humidity has brought body beasties mosquitoes, midges, minute white flies and little hard black biting flies ± 2mm long with transparent wings; they stick to clothes and skin but spring away too fast to be caught. When magnified these look like River Blindness flies, see the illustration in Reader's Digest January 1997 page 35. Information needed, how about it fishermen and fundis? These flies are a deterrent to tree walking in the morning and evening, they ignore insect repellents. A fly in the eye burns for a long time. A hat keeps in place the clothing which the gardeners wrap round their heads and necks to avoid these persistent pests.

Civet Middens
The linear civetry with all its exciting seeds and tree fruits beside the road has been dispersed by water borne sanitation into the vlei where we heard a lone reveller calling at 7a.m. this was a Greater Cross-marked toad; his sort made the strange nightly humming which we could not identify when we came to Tinto at the end of January 1988. Early in the mango season a civet came to eat the fallen fruit in the orchard. Recently discovered is a group of pure white ground orchids beside a civetry in Brachystegia woodland. Each plant has two glistening smooth round to oval silvery-green prostrate leaves, its leafless stem bears an inflorescence of several flowers at approximately 20cm from the ground. It was photographed on February 3.

Punica the Pomegranate
In November our son brought home a souvenir from the sand dunes near Pemba in northern Mozambique. The fruit was like a small green pomegranate, whose homeland is the Mediterranean coasts; is there a similar indigenous tree? Perhaps it is a garden escape? Any comments? Well-grown Baobabs were seen all along the tedious, rough route from Tete to Pemba.

A Task for Rainy Days
Some easily-ignored plant families are Cyperaceae, the sedges which vary in size from Papyrus, watergrasses and the diminutive Bulbostylis; other genera are Cyperus, Kyllinga, Scirpus and Ascolepis (not found yet), most of these have three-sided sharp-edged solid stems. Typhaceae includes the bulrushes Typha latifolia, their correct common name is reed maces. Juncaceae the rushes, green they grow but not here, no mention of Juncus species in local reference books. Phragmites sp. the reed seen in great numbers in sandy and silted up watercourses belongs to Poaceae the grasses, formerly Graminae. Collect the inflorescences of these moisture ¬loving plants during sunny intervals, they make a long-lasting arrangement to be studied at leisure! Little Bulbostylis can cope with arid conditions unlike most of the sedges. Bob Drummond named Scleria for me, it was found in this catchment; its family name is not recorded. Well labelled pressed specimens makes remembering their names much easier.

Msasa Moth
Pachymeta robusta, family Lasiocampidae, the Eggar Moths. We should look out for their larvae covered with long orange hair, they may be seen in daytime in clusters on trunks of Brachystegia spiciformis during February and March, the cater¬pillars travel to feed on the leaves at night. Their hairs are loosely attached and will remain embedded in the skin of anyone touching them, causing intense irritation. A grandchild with me found a communal cocoon made by the larvae; it was built around the base of a tufted grass along a fireguard. Some caterpillars’ hair is shed and woven into the cells of the cocoon for extra strength. Cells may be plastered on the inside with ground up soil making the walls very smooth ready to receive each pupa (chrysalis). Many thanks to Moira Fitzpatrick and her colleagues at the Natural History Museum in Bulawayo for this information. This lepidopterous edifice looks like a piece of sea sponge rather flattened.

Precipitation
The National Geographic magazine informs us that rain runs off, flies off and sinks off, that may be so, there is an awful lot of it lying on the surface these days, walks are limited to crest roads and high ground, nevertheless there is always something of interest, such as the high-up clump of Loranthus, the semi-parasite on which on closer inspection was seen to be a massive Maerua juncea (rush-like see paragraph above) its scandent stem was hidden by dense foliage on a termite mound. The high level of the dam has cut us off from fruiting Carissa trees, last season enough jelly was made for this year. This preserve is an adjunct to pork instead of applesauce. It sweetens oxtail casseroles.

Christmas Retrospect
The following species of woody vegetation were used to create a Bethlehem in Ayrshire scene in the fireplace in the sitting room at Tinto. Open dry fruits of Diplorhynchus, rough side up added to granite stones made rocky terrain; Protea angolensis and Protea gaguedi calyxes inverted made roofs of traditional dwellings; twigs of Olax obtusifolia and the stems of coarse Asparagus sp. made the Nyarupinda riverine fringe; the dam was a mirror fragment edged with sand, gravel and tufts of very fine grass, was the shoreline. The second contour was the site of the Nativity stable and a “musha” some distance away; natural rock for a Kopjie near and far, receded to the gentle angles of the Great Dyke along the wide horizon. In the foreground a small dead twig of Julbernardia bearing small fruits of Tropical Cinnabar Brackets added a touch of red to the greenery. Small children rearranged domestic animals and wild mammals at will; this completed the panorama. Much time was devoted to this on¬going scene as ideas came to mind, for the greater glory of God, A.M.D.G. And Majorem Dei Gloriam.
IBMG Raffingora 6 February 1999

The Tree Society’s e-mail address is
petra@mango.zw (Ruth Evans)