TREE LIFE

September 2000

While the present problems persist please check with any of the committee members to ensure that the scheduled outings and walks will actually take place. 

 

MASHONALAND CALENDAR

Saturday 2 September. Originally our Botanic Garden Walk was cancelled for two months but, happily for us, Tom insists that he is well enough to lead our walk this month; so we will meet Tom in the car park at 10.45 for 11 a.m.

Sunday 17 September. Back to another of our favourite haunts – Gosho Park near Marondera. This nature reserve is the property of Peterhouse College and this outing has been arranged by Rob Burrett who is teaching at Peterhouse and has made an extensive study of the Park, so an interesting day is guaranteed.  Turn left into the park. The security guard will admit you on presentation of your Tree Life. Meet at the camp site which Rob has reserved for our group. We will look at some patches of trees which appear to be different to others in the area, and after lunch Rob will take us to his Eastern Highlands outliers in the kopjies towards the north of the Park. Rob may still have his excavation open at the time and would be willing to show members and talk about the hole in the ground. Bring your lunch and a chair for a spring day in the bush.

Saturday 23 September. Mark’s walk will take us through the arboretum in Prince Edward School. Leslee Maasdorp planted most of the trees and we hope she will be able to accompany us on the walk. Meet at 2.30 p.m.

Tuesday 3 October. Back to summer time for our Botanic Garden Walk.

MATABELELAND CALENDAR

Sunday 3 September. Meet in the car park at Girls’ College at 8.30 a.m. for possibly a tree naming exercise on NUST campus.

Sunday 1 October. Lumeni Falls – south Matopos. In all cases please contact a committee member for confirmation.

 

WOODLAND, VLEI AND GRASSLAND

It was Dr. Oliver West who explained to me why trees did not normally occur in vleis and I have never had reason to doubt what he said. That was in 1966 when he was Chief Pasture Research Officer in the Department of Research and Specialist Services.
Vlei is a South African term derived from the Dutch word ‘vallei’ meaning valley. Common in sandveld in Mashonaland, vleis are gently sloping land depressions which are seasonally waterlogged due to restricted soil drainage. In the ‘dambos’ of Malawi and Zambia the phenomenon is more strongly developed, whereas in the lowveld, on account of the lower rainfall and greater evaporation, true vleis are uncommon.
Vleis in Mashonaland are characterised by a dense cover of grasses with Hyparrhenia spp. dominating. Trees are normally absent or rare. In the hot dry season when the grasses have senesced and dried off, the vleis can burn very fiercely. Vleis are the sponges in the hydrological balance that slowly release the water stored from the summer rains to maintain stream flow through the dry season. In order to sustain this dry season flow it is important that trees do not invade the vleis as they would have the effect of drying them out prematurely. Vleis also provide valuable thatching grass apart from useful grazing in the early summer before the rains start. Ecologically, they are important and should be preserved. But why are they distinct from woodland?
It is principally the seasonal waterlogging that makes them unsuitable for most tree growth but fire and, less so, frosts are ancillary factors. Grasses being shallow rooted and of shorter longevity, grow successfully on the poorly drained vlei soils but trees, being perennial with deeper root systems, generally require deep well drained soil. The soils above the vlei margins are better drained and therefore suited to a woodland climax, which in Mashonaland, is most commonly Brachystegia woodland.
But occasionally trees do occur in vleis, Acacia polyacantha (white thorn) and other acacia species, for example, encroach into vleis especially where periodic grass fires are absent. Whilst these species can evidently tolerate a degree of waterlogging, they are sensitive to fire damage especially when young. As veld burning becomes less common, so encroachment increases. Severe frost may also kill young acacia trees.
Similarly, Syzygium guineense (water berry), a tree renowned for its unusual ability to grow in permanently wet spots along perennial streams, is extremely sensitive to fire damage and therefore normally does not grow in vleis except where the surrounding grass remains green and non inflammable.

Interestingly, a subspecies of Syzygium guineense, is well adapted to survive within a vlei environment although not easily seen. This is Syzygium huillense which is unusual in that the contorted stem is prostrate just below the soil surface where it lies protected from fire and frost. Each year low foliage growth emerges from the stem. This ‘tree’ species is better known for its ornamental value as the contorted subterranean stem is collected as a form of driftwood.

But perhaps the most common incidence of trees in vlei land are those growing on termite mounds which present a favourable habitat for tree colonisation because of the free drainage. Diospyros lycioides (blue bush or red star-apple) is common in such colonies often with Schotia brachypetala (Boer-bean or fuchsia tree). The mound, being elevated, also affords a degree of protection against fire. These ant-heap tree colonies do not impair the sponge attributes of vleis and are not harmful.
Regular frosts, as those which occur in vleis at the higher altitudes, especially as cold air tends to drain and settle into these depressions, can kill off the shoots of woody plants and so discourage their invasion into vleis. Frost also has a less direct effect in that it kills off the top hamper of grasses making for a hot fire later in the season which in turn is more damaging to any trees attempting to gain a foothold in the vlei.

In the lowveld, true vleis are seldom a feature of the landscape. Nevertheless, there are open grass¬land areas, not necessarily depressions, as typified by the deep basalt clay soils which extend in a belt south-westwards from Chisumbanje to the Mateke Hills. These soils are mostly free of tree growth especially where slopes are shallow and surface runoff is slow. Urochloa spp. commonly dominates in these grasslands. The basalt soils are extremely fertile in nutrients and have a high water holding capacity and are often referred to as self-churning clays on account of their plasticity. On wetting they swell into a structureless mass but, as they dry, they shrink with great force to form deep cracks and the surface layer crumbles.

It is this forceful cracking upon drying that has been suggested as being the factor that prevents trees from growing on these soils. Roots have been seen to have to have been ruptured in these cracks. However, it is well known that trees generally can endure heavy pruning both to aerial parts as well as to roots without succumbing. And it is also true that in other areas, broken roots will commonly regenerate into coppice growth as seen in recently slumped and ripped fields, providing the soil conditions are satisfactory. So the reason for the general absence of trees on these soils may lie not in the cracking phenomenon, but in some other factor.

When dry, the cracks allow rain water to enter the soil until the resultant swelling from wetting closes the cracks and water movement then becomes very restricted due to the extremely fine texture of the clay particles and the lack of crumb structure. The soil remains saturated and poorly aerated, until the drying process by evaporation from the soil surface aided by transpiration by plant roots reaches the cracking and crumbling stage again. This seasonal waterlogging will militate against tree growth, the same process as in the waterlogged vlei. Mopane (Colophospermum mopane) does occur on these grasslands but usually sparsely and often in stunted suffrutex form with, interestingly, a prostrate, contorted and highly weathered stem, not unlike the prostrate Syzygium huillense found in true vleis and described above.

Zimbabwe is known for its woodlands and, apart from Man’s activities, the ecological distribution of these woodlands is governed in the main by the degree of free soil drainage. The natural grasslands, other than the montane grasslands, occur on soils which are seasonally waterlogged and which are unsuitable to most tree species except those few that can stand ‘wet feet’.

The natural grasslands of the montane regions along the Eastern border of Zimbabwe are mostly fire induced grassland climaxes as they occur on exceptionally well drained soils of these high rainfall areas. It is unfortunate that they are evidently subject at present to encroachment by introduced plantation species of pine and wattle, the eradication of which is probably best achieved by hand grubbing or hand applied arboricides. Although in theory able to eradicate the encroachers, fire in these high rainfall grasslands can be extremely damaging to the indigenous forests of which there are now only isolated remnants in fire protected localities.

John H.Wilson

 

BULAWAYO BRANCH OUTING  6th AUGUST, 2000

It was a nearly perfect day; except for the wind. The bite in its breath betrayed its Antarctic breeding. Mind you, this day did not have that auspicious a beginning! When I locked my gate I observed on it the fall-out from the foggy-foggy dew that had shrouded the landscape some hours earlier. Fast moving clouds came up and obscured the sun, and it was only when we arrived at our destination that they cleared and drifted away, leaving a cloudless sky.

A jumbo jet was now visible, so very high that the sound of its engines only reached us after it had passed. But the vapour trails from the four engines were dramatic proof of its passing.

The Bulawayo Branch of the Tree Society had found a wild, quiet tract of land, where it could wander peacefully, without troubles! This is land owned by the Municipality of Bulawayo, designated as a recreation area for all its citizens.

In places the geography and flora superficially resemble those at the Matobo Hills. There are granite outcrops. Pink Peeling Paper-bark trees abound (Albizia tanganyicensis).

There was a vast expanse of fairly flat granite rock, surrounded by trees. On this rock were to be found many of the curious succulents called Anacampseros rhodesiaca. The minute plants are easily overlooked, resembling as they do, tiny weenie remnants of paper that has been torn up and scattered. After the first rains, they will flower, putting forth white or pink blossoms of incredibly delicate beauty. These flowers only open in the afternoon. As the whole plant is wedged frequently in between the cracks in the granite, one is lucky to find them in flower, as they are only a few millimetres in height.
However, the ultimate in disguise was a Delosperma that littered the ground like dis¬carded pieces of string, and which hardly merited a second glance.

It is a grand place for Commiphora. Altogether we found more than seventy-two different trees or shrubs, which included six Commiphora – Commiphora marlothii, Commiphora mollis, Commiphora schimperi, Commiphora africana, Commiphora glandulosa, and Commiphora mossambicensis.

There were four species of Combretum – Combretum apiculatum, Combretum collinum, Combretum molle and Combretum zeyheri, and fourFicus  sp. – Ficus abutilifolia, Ficus glumosa, Ficus ingens and Ficus thonningii. And four species of Grewia – Grewia bicolor, Grewia flava, Grewia flavescens, and Grewia monticola.

There were plenty of enormous Kirkia acuminata. Some of these had been felled, and the middle sections of the trunks extracted. Jean imparted the knowledge that these trees are much in demand for carving because their wood doesn’t need to be cured before being used, and subsequently doesn’t crack.

Four eagles soared by. They could have been brown snake eagles. They reminded me of the song in “Oklahoma” which mentions a hawk making lazy circles in the sky and how “we belong to the land, and the land we belong to is grand.”

I marvelled how these great birds, in their anonymous brown plumage could, so effortlessly, sail against a stiff wind without flapping their wings or ruffling a feather.
Very far away, I could hear a Chin-spot Batis singing its spring song, “Three blind mice.” A Brubru shrike interposed its twin notes. This bird is the only one I know that can sing two notes simultaneously. They are less than a semitone apart.

Surprisingly sparse, both in distribution and number were the Acacia trees. There were only three representatives present of this normally prolific and prominent family – Acacia ataxacantha, Acacia nigrescens and Acacia nilotica, and these occurred singly, in isolation from each other. No doubt due to the excellent rainy season we have just experienced, many trees still carried their foliage, making identification so much easier.

The Aloe excelsa were all magnificently in flower. As many of these were extremely tall, their trunks and red or orange flower spikes protruded above the canopies of the surrounding trees.

We lunched in one of the seemingly barren patches of sodic soils that always accompany the Mopane woods. Here were many small Commiphora and a simply splendid hybrid Aloe excelsa X aculeata. It stood as high as a neighbouring pure Aloe excelsa. However the racemes of the hybrid panicle were much shorter, stubbier and thicker than those of the pure species. The opening flowers showed the typical yellow colour associated with Aloe aculeata and absent from Aloe excelsa.

Anthon remarked that the racemes of the local Aloe excelsa all pointed nearly vertically up¬wards and differed in this respect from those in other places in the country, where they are inclined to be more angular.

Several small succulents clustered in great pro¬fusion at the bases of the Mopane trees. These were Crassula, Kalanchoe, and one stapeliad, Duvalia polita.

Eventually it was time to return to town. Anthon, we thank you for sharing this place with us. We had a lovely day, and we are also grateful for your imparted knowledge.

Norma Hughes

 

Nyarupinda Catchment July 2000

The Scene
It is the 28th July and the cool dry season is with us, among many vegetation delights are garden peas and sweet peas. So far this month the crack o’ dawn temperature has dropped to 5 degrees C on five occasions. Since the hot wet season ended there has been more cloud than usual; those clear bright sunny days beginning with crisp mornings have been less frequent.

A temperature inversion nearby was an event to photograph, at sunrise, a clearly defined lake of mist filling the valley opposite this house. Water and a few tall tree islands reached a shoreline halfway up Jese kopjie five km distant. Upon rising the impact of this view will always be remembered as Lake Nyarupinda.

Figs and Birds
This morning has been rather unsettled because the calls of Green pigeons (Treron calva) and Meyer’s Parrots (Poicephalus meyeri) have demanded attention. They were not feeding but probably attracted by a splendid crop of small green furry figs on Ficus thonningii, one of these is inside the fence around Tinto hill, another is outside at the level of surrounding ground. This is the ‘lowveld’ where an introduced Baobab now has a soil level girth of 112 cm, a wild mango Cordyla africana has a circumference of 85cm and has not flowered yet, this sight is eagerly awaited, a profusion of yellow.  Other smaller trees are lowveld fig Ficus stuhlmannii,  has produced its delicate small orchid-like blooms at three consecutive Christmas times. There is a mopane, Colophospermum mopane tall, stately and virginal, hasten the time when antelopes browse under it.

There have been three avian visitors to the house this month. Today a Meyer’s Parrot left the flock and inspected the level top of the double chimney for quite a while, enough time to nip away and get the binoculars. It was intent on something up there, wire-netting covers the openings; occasionally the wood fire is needed, a hot spot for a nest and smoky too. A Lesser Striped Swallow Hirundo abyssinica flew round and round among the kitchen rafters until at long last it came lower, settled and saw the open door to freedom, whilst inside we hoped it had a meal of aerial arthropods. On another occasion when sitting in the kitchen in the sunshine, beating some¬thing for a cake and when having a breather a little bird came down from the roof and sat on my knee for a few moments. It looked about and pecked once at my apron, it moved to my chest, possibly attracted to the diamante floral design on a scarlet tracksuit top. Beside me was Ken Newman’s bird book open at the sunbirds and here was one on my lap. Beating resumed when it left, then there was a flurry beside my head, a lull, and then another flurry which suggested that it had settled on my back – so lightly – it was not felt. This fearless little bird was a male miombo Sunbird a double-collared Sunbird, Nectarinia manoensis.

A Very Late Item from January 2000.
Approximately 10 male foam nest tree frogs have had their breeding domain invaded by many hundreds of small dark grey mottled snails feeding on algae at the water line and below where they attach themselves to the wall of an open reservoir. These gastropods (belly-walkers) are water bird and otter food; it would benefit us if something came to devour the snails before they block the outlet pipe. The invasion ended when the reservoir had its occasional empty and scrub.

A Woodland Observation.
Something unusual happened in the Brachystegia woodland when the rains were more or less established early this year. The presence of variegated and some completely white foliage on a large number of different kinds of plants. Lowly subjects affected were a running grass, blackjack seedlings, Makoni tea bush, Adenia goetzei, white-flowered Pentas and a Dyschoriste. Samples of trees collected were Lannea discolor, Bauhinia petersiana, Senna singueana, Euclea divinorum (always so dark green). A sapling of Acacia sieberiana, Combretum molle, Steganotaenia araliacea carrot tree had the first white-edged green leaves, these alerted us, and thereafter the list was made. New growth of semi-parasite Tapinanthus sp. on Chinese lantern tree Dichrostachys cinerea growing in full sunshine, was white. Annually this broad-leaved woodland has normal leaves, the canopy is not dense and light intensity is that of speckled shade. Cattle have disturbed most of this terrain. Doubtless a solution to this question of lack of chlorophyll will be forthcoming in these pages. Has this aberration been seen elsewhere?

Civet News.
Their menu has changed to include Sucking porcupine, bananas, decorated, or rather, garnished with silver paper and red and white wool.

Temperature just at dawn today was 5½ºC in the carport on the first level below the house, 2½ºC in the ‘lowveld’ vegetable garden.

That is all today July 29th 2000. Keep your spirits up.

-Benedicta Graves

 

SEEING RED

Everybody knows tomato plants can’t see. So why is it they produce more tomatoes when they are surrounded by the colour red?

Michael Kasperbauer, a plant physiologist with the Department of Agriculture’s Coastal Plains research station, in South Carolina, has discovered that if you surround tomato plants with a red plastic mulch (a mod version of that stuff gardeners spread around trees), they’ll increase their productivity by as much as 20%. What it comes down to, he says, is competition. Tomato plants, it seems, respond to a type of red light called far-red. Among the plant’s proteins sensitive to the far-red light units, or photons, is a tiny pigment called phytochrome, which basically functions as the CEO of plant growth: When the far-red photons hit the plant, the phytochrome takes it as an indication that it’s surrounded by voluptuous tomato-producing neighbours. Not to be outdone, the phytochrome directs the aboveground portion of the plant to get moving. And the plant responds by producing in force.

The strange thing is, the far-red light the phytochrome senses isn’t even coming from the neighbouring tomatoes – it’s bouncing off the plant’s leaves. In some weird twist on colour blindness, plants see far-red where humans see green. This Kasperbauer can’t explain, saying only, “Of course a tomato can’t see!”

R E Sullivan, Jr.

The preceding article appeared in the April 2000 issue of Gourmet magazine. To those who still remember Kim Damstra’s article in Tree Life 199 – Why do young leaves flush out red? there is no great mystery to this “weird twist on colour blindness’. In his article Kim explained how plants use and absorb red light and reflect away the complementary colour, green – which is what we see as being the colour of a leaf. Having more red light around, whether from the plastic or neighbouring fruit, would enhance the ‘red-wavelength feeling’ of the tomato plant.

However, I must confess that I am still slightly confused with Kim’s article which used red, blue and yellow as the primary colours, and green, orange and purple as the secondaries since those primaries are not the “true” primaries, but are psychological primaries (along with green, black and white) used in art and advertising! Whilst not great on physics, I understand the (subtractive) primaries to be magenta, cyan and yellow and the resultant secondaries green, red, and blue, resulting in a quite different colour wheel! Perhaps if any reader is interested we can clarify this issue at some later date.

-Ian Riddell

 

In Retrospect continued. By Lyn Mullin

ANCIENT WISDOM
The following is a brief extract from a longer note by George Hall, titled THE IMPORTANCE OF REGROWTH and published in TREE LIFE No.31 (September 1982):
The ancient wisdom, found widely where tribal tradition is still strong, whereby trees harvested for fuel or poles are cut off at about waist height, is not the idleness I have sometimes heard it labelled. This custom ensures that the [coppice] regeneration would get away quickly, and get above the dangers of fire, frost, and browse in the first season. In many densely populated communal lands demand is such that this ancient wisdom cannot now be followed, and the result of clear-felling down to ground level, where the first season’s growth is neither as strong nor as fully protected from danger, is seen in devastated areas that one does not have to travel far from the capital city to find.

NATURE INTERTWINED
The following article by Meg and Paul Coates Palgrave was based on thoughts by Trevor Gordon, and was attached to TREE LIFE No.34 (December 1982):
The identification of trees and plants is no easy matter for the layman. However, if a real interest is taken and keen observations made, the task becomes easier and infinitely more interesting. Habitats, such as granite kopjies, river banks, or open woodland; seasonal variations, such as spring or autumn leaf colours, as well as the times of flowering (for instance our proteas and the two commonest cassias can easily be identified by the time at which they flower). Altitude can often be critical, and the general shape or field impression of the tree, often scorned by the botanist who has long since passed that stage, may be so helpful to the beginner. One of the most beautifully shaped trees is the Mobola plum, Parinari curatellifolia; it always seems to have been pruned to a perfect toadstool shape. And, in contrast, the Muwanga, Pericopsis angolensis, with crooked, pearly stems that, no matter how much they bend and twist, always end with the leaf canopy in perfect symmetry.

Examination of the bark is not only very helpful, but in many cases reveals consistent characteristics – the delicately coloured, peeling bark of Ochna pulchra (pulchra means beautiful). The malaria-yellow bark of the fever tree, Acacia xanthophloea; the bark of the paperbark Commiphora, Commiphora marlothii, and the paperbark Albizia, Albizia tanganyicensis, peeling in sheets of yellow and red paper respectively, and the rainbow colours of the bark of the tick tree, Sterculia africana.

Closer examination can be even more rewarding. Little tips can be found that will always be recognizable in the future. For instance a 1 mm-diameter, pale gland found at the junction of the leaf-stalk and the blade of the leaf tells immediately that this is a species of Monotes. This little gland is an extra-floral nectary, which only means that a nectar-producing organ, for some reason, is not in the flower, but on the leaf. It has been seen to exude its nectar, which dribbles down the leaf stalks, and is eagerly sought by ants.

Talking of ants, many insects can be a great help with identification. Butterflies are very particular in choosing the right food-plant for their caterpillars, and land briefly on one plant after another, tasting them with the taste-buds on their feet, then leaving that tree to taste the next, repeating the performance until the right one is found. Then, and only then, will they lay their eggs. This ‘tasting flight’ is quite characteristic and recognizable, and when finally the egg is laid the plant is identified! Not quite, actually, as each female butterfly has a short list of plants that she will accept, but it narrows down the field a great deal. To illustrate the point, the swallow¬tail butterflies favour members of the citrus family, Rutaceae, but each species of swallowtail uses only a few members of that family as food-plants. For instance in the Murahwa’s Hill area at Mutare, the Mocker Swallowtail lays almost exclusively on Teclea nobilis, and the Emperor Swallowtail on Fagaropsis angolensis, while the Citrus Swallowtail is so called for its prevalence – to the extent of becoming a pest – on citrus trees.

Recently, at the Matopos, our attention was attracted to a tree by the fact that Citrus and Green-banded Swallowtails were laying on its leaves. As we immediately suspected, it proved to be the Cape chestnut, Calodendrum capense, and as an added bonus it was in full flower.

Moths are usually haphazard layers. Every¬one must have seen moth eggs laid on walls and windows or anywhere, laid close together in a bunch, whereas butterflies usually lay them singly, dotted around the leaves. Not, however, the moth of a gregarious caterpillar, Diapalpus congregarius, which meticulously chooses Cassia leaves for its young to eat, almost exclusively the winter cassia, Cassia singueana (Trevor Gordon records finding only one on a long-pod cassia, Cassia abbreviata). The caterpillars build an untidy drooping nest of spider-like web in which to spin their cocoons. Even after they have long-since hatched and flown away this nest remains as a label with Cassia singueana written on it.

Take a moment, now, to think also that to an entomologist studying butterflies, a nest of cocoons on a Cassia tree is a label with Diapalpus congregarius written on it. Consider, too, that this entomologist, finding cater¬pillars on a Cape chestnut, would immediately look up swallowtails in his book.

This is how closely all sections of nature are intertwined.

[Comment 2000: Cassia singueana has been reclassified as Senna singueana, and it would seem that the moth, Diapalpus congregarius, knew all along that Cassia and Senna were different genera. The one moth that Trevor Gordon found on Cassia abbreviata might have been disorientated for one reason or another!).

Parasitic wasps of the Braconid species are highly selective in the caterpillars (and other insects) that they parasitize. Their ovipositors (egg-laying tubes) puncture the victim’s body, and they lay their eggs deep inside. The grubs hatch and feed on the flesh around them (being careful not to destroy any vital organs) until they mature, when they bore their way out of the body, and weave their cocoons outside. An examination of the cocoon on the back of the caterpillar will certainly identify both caterpillar and wasp.

Here, of course, we come into the fascinating area of biological control, where the prickly-pear plague of South Africa was eliminated by an insect, and the rabbit plague of Australia was controlled by a virus. A dangerous science, where the beneficial predator can so easily become a pest in itself, but, properly controlled, very full of potential.

Many plants display galls which, our scientific dictionary says, are excrescences caused by fungi, mites, or insects. With some tree species the presence of galls is so characteristic as to give the clue needed to make identification. The sight of a silver Terminalia, Terminalia sericea, in stark winter leaflessness but covered in galls, is quite unmistakable. The pods of wing-pod, Xeroderris stuhlmannii, can be so attacked that the tree seems to be covered in berries, which is most misleading until the discovery of one [unaffected] pod reveals the secret. And the infection of the flowers or fruits of the water-berries, Syzygium spp., to form distinctive tangled black masses, so easily identify the trees.

Look around you and note everything. The swift, flashing flight of the beautiful Charaxes butterflies to a ‘sucking tree’ that is exuding a sap they enjoy. A tree raining water to form pools beneath it in the hottest, driest month of the year means the presence of a frog-hopper insect infesting the tree, and sucking its sap so voraciously that it is running in froth out of its body. This would almost certainly be the rain tree, Lonchocarpus capassa (but there are a few other possible species), and the insect would be Ptyelus grossus. As a protection against the heat it covers its back with this froth, commonly called cuckoo spit in other closely related species. Birds clustering in a tree will draw attention to edible fruit or nectar-filled flowers; a browsing giraffe prefers Boscia and Acacia species, and a square-lipped rhinoceros eats mainly the perennial species of grass.

Heavy metals, such as nickel, chrome, copper, and arsenic are extremely toxic to plants. That is why parts of the hills of the Great Dyke are so characteristically bare of trees, and close examination will show that the grass is a species tolerant of the heavy metals. On the Wedza Mountains there is the ‘nickel anomaly’, an area where the concentration [of nickel] is such that only 17 species of grasses, herbs, and trees have been found. One woolly herb, Dicoma macrocephala, seems only to grow on nickel-bearing soils, and has thus earned the name ‘nickel flower”. Similarly, Becium homblei is the ‘copper flower’, and, even more specifically, certain groupings of species give more accurate indications of certain metals.

The potential of the vegetation as a guide to locating economically important minerals has been recognized for a long time, but it is only recently that the matter has been treated seriously. This study can be divided into two sections. (1) Geobotany, which is the recognition of indicator species, the tolerant ones strongly suggesting the presence of the metals; and (2) Biogeochemistry, which is the chemical analysis of certain parts of the plants to find out the concentration of the metal in the soil. Research is making this study more exact all the time.

Disturbed ground around the foot of a tree immediately raises the question: why? Are the roots edible to man or animal, or have they been sought after by a medicine man for his potions? Bark stripped from a tree raises the same questions. One should always notice everything, and question everything. One cannot study just one facet of nature; all the other facets keep getting in the way. But the more they get in the way, the more one realizes how fascinating nature can be.

In Retrospect will be continued.

 

THE LAMPATIA AT HARARE FOREST NURSERY

Among the early introductions of forest trees at the Harare Forest Nursery, off Orange Grove Drive in Highlands, was a specimen of Duabanga grandiflora (formerly Duabanga sonneratioides). It belongs to the small botanical family Sonneratiaceae, which comprises two genera only – Duabanga (2 rain¬forest species) and Sonneratia (5 mangrove species). Duabanga grandiflora is a large forest tree from India, Burma, Nepal, and the Andaman and Nicobar Islands. It is known as lampatia in Nepal, khokan in Assam, and myaukngo in Burma. It produces a soft wood that is easily seasoned and is excellent for making tea chests. It has also been used for making canoes and for the manufacture of matches.

The single specimen at the forest nursery is probably the only one of its kind in Zimbabwe, and although there is no definite record, it must have been planted around 1907. In February 1986 it had a height of 25.5 metres and a diameter of 91.3 centimetres, which is close to the dimensions it commonly attains in its native habitat. It is an untidy-looking tree with un¬pleasantly scented flowers that appear in clusters at the ends of the branches. The tree requires a warm, moist climate, so it is rather out of its element in Harare. In recent years there has been a lot of die-back of the crown, and I suspect that it will not be with us for very much longer.

-Lyn Mullin

Mr. Lyn Mullin has done a great job compiling a list of Ndebele plant names from three main sources, (1) FL Orpen (1951), Botanical-Vernacular and Vernacular-Botanical Names of some Trees and Shrubs in Matabeleland. This was originally published in the Rhodesia Agricultural Journal, Volume XLVIII, No. 2, pages 165-181, March-April 1951, and reprinted as Bulletin No. 1573 in the same year. (2) H. Wild (1972) A Rhodesian Botanical Dictionary of African and English Plant Names, revised and enlarged by H.M. Biegel and S. Mavi. And (3) J. Timberlake, C. Fagg, and RD Barnes (1999), Field Guide to the Acacias of Zimbabwe.

The list is available to members for $50 to cover paper and postage, or on a computer disc supplied by yourself, or by e-mail.

Please contact Maureen Silva-Jones.

 

ANDY MACNAUGHTAN   CHAIRMAN