TREE LIFE

December 2000

As before please confirm with any of the committee members that the scheduled outings and walks will actually take place. 

 

MASHONALAND CALENDAR

Sunday 3 December. This is a combined Christmas social and sadly our official farewell to the Haxen family who will shortly be emigrating to Oz. By popular request Tree Bingo will be played amongst the more than 120 tree species growing at “The Shambles”. Although this will be Phil’s ‘swan song’ as MC he will still resist obvious bribes. If the weather is fine there will be facilities for braaing, so bring a chair, a wine glass, lunch of your choice and something of a Christmas nature to share, and we will meet at 9.30 a.m. for a memorable day. Don’t forget to bring a pencil.

Tuesday 5 December. Botanic Garden Walk. Meet in the car park of the Botanic Garden where we will meet Tom at 4.45 for 5 p.m. If there is a topic that you would like Tom to discuss please contact any of the Committee members.

Saturday 23 December. Mark’s Walk will be to that exciting spot Domboshawa.  (On our last visit this was $5 per person)

Tuesday 2 January. Botanic Garden Walk.

 

MATABELELAND CALENDAR.

Sunday 3 December. To Lumene Falls in the southern Matopos. Some people may go a day beforehand to camp overnight, others can join o. Sunday. Please confirm with Jonathan Timberlake,  J. P. Felu  or Anthon Ellert,

14 December 2000. David Attenborough videos: ‘The Private Life of plants’ will be shown at 18.00 hours at JP’s place .

1 January 2001. There will be the traditional New Years Day party at the Timberlake’s, . Please bring your own drinks and contribution to food. Please phone Gill Short to confirm and for organising food.

 

GOSHA PARK, MARONDERA: 17 SEPTEMBER 2000

A good number of members turned up at Gosho Park on a warm Sunday morning, Rob Burrett described how Peter Ginn established the park in the early 1980s and consists basically of the rocky part of Springvale School. In understanding the vegetation, it is important to realise that both the altitude (c.1640 m) and the rainfall are relatively high.

We first crossed an open grassy area in which there were a number of suffrutex species. These are usually defined as small shrubs which produce usually annual flowering stems from an underground woody rootstock. They are a common element of the Zimbabwean flora and often occur in areas that are burnt every season.

Species seen included the first signs of the tiny Lannea edulis with its flowers and fruits barely above ground level, Euphorbia cyparissioides (dense, spirally arranged linear leaves with flowers in terminal umbels) and Syzygium guineense subsp. huillense.

I understand from Meg Coates Palgrave that there is a controversy as to whether this really differs from the normal subsp. guineense or whether it is simply a form created by its habitat.

Perhaps the most extraordinary thing was the abundance of an exotic composite, Ageratina adenophora (Eupatorium adenophorum). We had seen occasional patches of its white flowering heads as we drove along the main Harare to Mutare Road, but in the park it has become seriously invasive. To some extent, it has colonised dry areas, such as an area of cleared gums, but its main and preferred habitat was along the stream and vlei systems where it occurred with extraordinary lushness to heights of 2,5 metres, it is in many ways a strikingly beautiful plant – tall, white-flowered and like many weeds, winter-flowering. It is a native of Mexico. One wonders how long it will be before it fills the stream systems around Harare and other parts of the country.
We stopped and looked at the trees on a small rocky kopjie. Here was the first cabbage-tree of the day – the species of high rainfall and/or rocky places, Cussonia spicata. Also, the striking shrubby Vernonia, Vernonia myriantha, which at certain times of the year has striking stipule-like structures at the base of the leaves (hence one of its former names, Vernonia stipulacea). I, and I think others too, have confused it with Solanum mauritianum, which, when it has no flowers or fruit, is somewhat similar looking and also has large false stipules. An easy way to separate them with a lens is to see if the plant is stellate-hairy or not – if it is, it is the Solanum.

A very common species in the Park is Diospyros whyteana (the Bladder-nut) with its glossy dark green leaves and margin ciliate with long hairs and the fruit which are enclosed by a large inflated bladder-like structure, which is in fact the enlarged calyx. Also common was Sericanthe andongensis, a shrub with white flowers, the lobes of the flowers are often slightly curved thereby resembling a Catherine wheel. Both are typical of high rainfall areas.

After lunch we took the cars and parked near a small dam and from there walked towards Rob’s dig. On the way we stopped at a rocky hill with huge boulders and saw an enormous flowering Erythrina lysistemon. This is the one which is probably most common in the E districts but which also occurs elsewhere in higher rainfall areas. Also there was a second species of Cussonia, Cussonia natalensis and some large Celtis africana.

After crossing a stream near a vlei, a fine colony of Ficus verruculosa (the Water fig) was found. This occurs in wet places and is usually a small plant. Also here were the very glossy dark green leaves of Rhamnus prinoides (Shiny leaf).

Shortly after we reached the site of Rob’s dig in the shelter of a large boulder and Rob kindly spent some time explaining the background and purpose to his work. Returning, Rob took us to some dense riverine vegetation, which consisted mainly of evergreen species. Here was Mussaenda arcuata (a climber really rather than a tree), Ilex mitis (Cape holly) and a puzzling species, which we eventually concluded must be Apodytes dimidiata (the White pear). A most interesting species for me was a climbing legume, which was in fruit with the pods split open and the seeds still adhering to the fruits; this was later identified as Dumasia villosa. It is a local species and is known from this area but was new to me.

Next we went to a rocky area with some enormous Euphorbia ingens (the naboom) and a solitary, damaged specimen of a Wild banana, Ensete ventricosum. Also here in the humus-filled gaps amongst the rocks grew a true stinging nettle, Girardinia diversifolia.

Returning to the cars a bit of a panic took place, as we believed that one of the members was missing – we actually failed to see her note saying she had gone back to the Bush Camp. The party then split up to search in various places – but eventually she was found.

All in all, a most interesting day and our thanks must go to Rob for organising it on our behalf.

-Mark Hyde

 

A WALK IN THE FYNBOS

A day off from an actuarial convention in Cape Town gave Linda and I an opportunity to visit Kirstenbosch Botanical Garden. From the Gardens we were able to walk on well-marked and well-signposted paths up into the vegetation clothing the lower parts of Table Mountain.

Having read about the Cape flora but never actually experienced it before, it was an absolutely fascinating experience. Along the streams running off the mountain was dense woody vegetation, which included what appeared to be a significant familiar component: e.g. Diospyros whyteana, Halleria lucida, Ilex mitis and Myrsine africana. These were mixed with totally unfamiliar species; but luckily some plants were labelled and it was interesting to see Brabejum stellatifolium (a Proteaceae with leaves whorled like a Macadamia).

Up in the fynbos, the impression was indeed similar to Nyanga – reinforced by the ubiquitous bracken, the commonly ericoid herbs and shrubs and the strong aromatic scents. Indeed, both the families and genera were often similar: Erica, Lobelia, Protea, Polygala, the numerous Selago-like species, what appeared to be species of Thesium and some very beautiful plants in the Thymelaeaceae. In addition were the extra¬ordinary cone-like flower heads of the Bruniaceae, many species of Pelargonium, the strange restios and of course abundant legumes and composites. It was a fascinating and as usual somewhat frustrating experience, mainly because the admittedly useful popular wild flower book we had bought did not, and of course could not, cover everything.

This year a Conspectus of the Cape Flora has been published (as no 9 in the series known as Strelitzia). This is basically a condensed flora; it lists with very brief description the 9000 species which occur in the “Cape floristic region” and includes keys to the families and genera. Perhaps we should think again about a Tree Society visit to the Cape?

-Mark Hyde

 

SOLAR ECLIPSE – 21ST JUNE 2001

Being outdoor types, Tree Society members will have heard about the total eclipse of the sun forecast in June next year.

This total eclipse of the sun by the moon will take place on Thursday 21st June 2001 between 13.12 and 13.20 hours over the north-eastern parts of Zimbabwe.

That day also happens to be the solstice, the shortest day of the year for us in the southern hemisphere, but that is completely coincidental.

The late C.B. Archer in a comprehensive article published in Zimbabwe Science News, April / June 1992, drew attention to the fact that, while partial solar and lunar eclipses are not uncommon in this region, the last total solar eclipse visible in Zimbabwe occurred 115 years ago in August 1886. For the historically minded, that was before the occupation of the country by the B.S.A. Company, when Francistown and Tati were the very edge of anything resembling civilisation to the north bound adventurers and explorers that passed that way.

At that time concession seekers were actively pressing King Lobengula for mineral rights in his and adjacent territories. So long ago!

The forthcoming total eclipse of the sun by the moon will result in a shadow which will track in a belt about 150km wide across the north-eastern parts of Zimbabwe from Zambia to Mozambique. The southern edge of this shadow track will be in a line between Makuti, Mvurwi, Shamva and Mutoko. To observe the total eclipse properly one should be north of that line. South of that line the eclipse will be partial.

So favoured viewing spots will include places like Chirundu, Mana, Horseshoe, Centenary, Mtepatepa, Mt. Darwin and Nyamapanda including all places in between them. Being winter, the sky should be cloudless affording a clear atmosphere for excellent viewing but REMEMBER ON NO ACCOUNT SHOULD YOU LOOK AT THE SUN DIRECTLY. MAKE SURE YOU USE SUITABLE FILTERS TO PROTECT YOUR EYES.

A very helpful article by Paul Murdin has been published in the July / Sept issue of Wildlife Zimbabwe with maps showing the pathway of the eclipse shadow together with times which will help you find a good position for viewing. You don’t have to be at a swanky resort. That is optional although the occasion will be something to celebrate. Anywhere in the countryside with a clear view of the sky and within the eclipse track will do. The phenomenon will occur at about lunch¬time on that Thursday and the sun will be high and slightly to the north. There are numerous tarred roads accessing the area but the closest for Harare residents will be north from Mvurwi, Bindura and Shamva.
The birds will be baffled at the sudden and short-lived dusk and animals may behave strangely, too. Perhaps our birding colleagues will advise us of special places where we might best witness this strange bird behaviour.

For the statistically minded, Archer gives the next total solar eclipse as on the 4th December 2002, a relatively short gap of 18 months, but this will be over the western border and the northern Transvaal. It will be a further 93 years before the next one in Zimbabwe in June 2095 and it will track across Gwanda, Masvingo and Mutare.

Thursday, the 21st June 2001, will not be a fizzle like the last unfortunate viewing of Halley’s Comet. Do not miss the spectacle. For those of us residing in the northeast sector of Zimbabwe it will be an event of a lifetime with prime atmospheric viewing conditions as well – free! Something to celebrate.

-John Wilson

 

A SAFE HAVEN FOR SEEDS HARRY BARTON ROYAL BOTANIC GARDENS, KEW

One quarter of the world’s flowering plant species could disappear within 50 years. A mass extinction on this scale would seriously restrict the options for survival available to future generations, but help is at hand. The Royal Botanic Gardens, Kew’s Millennium Seed Bank project will safeguard over 25 000 species of plant against extinction.
Extinction of species on a global scale is undoubtedly one of the major environmental concerns of our time.

Professor E 0 Wilson of Harvard University has described the ongoing loss of genetic diversity as ‘… the folly for which our descendants are least likely to forgive us’. While rates of species condemned to extinction are difficult to predict accurately, recent estimates suggest a rate of 5.8% per decade, or 29% of all biodiversity within the next 50 years (WCMC, 1992). What makes extinction of such concern is its irreversibility – vegetation may regenerate on degraded land, if left undisturbed for long enough, but an extinct species can never be reproduced. Furthermore, we do not know how the loss of individual species is likely to affect the functionality of ecosystems as a whole.

Following the Rio Summit, in 1992, it became clear that the solutions to loss of biodiversity lay in global cooperation, as well as in the action of individual nation states. One of the outcomes of the Rio Summit was the Convention on Biological Diversity, which has since been ratified by 169 countries, including the UK. The Convention highlights the importance of ex situ conservation – conserving species in botanic gardens or seed banks, for example – as a back up where the security of species in situ cannot be guaranteed.

As part of its conservation programme, the Royal Botanic Gardens, Kew has operated a seed bank since the late 1960s; this is based at Wakehurst Place in Sussex. The seed bank currently holds the seeds of over 4000 wild flowering plant species. In the light of Rio, and the ever-accelerating rates of biodiversity loss, it was decided to plan dramatic increase in the scale of the conservation programme for the year 2000. This new project, the Millennium Seed Bank, has been part funded by the Millennium Commission, the Wellcome Trust and Orange PLC, and will con¬serve approximately 25 000 species of wild flowering plants. The need for a seed bank on such a large scale was underlined by a Kew study, which showed that whereas ample seed banking facilities existed for crop species, similar facilities for wild species were practically non-existent (Smith and prance, 1997).

What is a seed bank?
Seed banking is, in effect, a means of preserving plants in a state of suspended animation. Live seeds are collected from plants growing in the wild. After cleaning and discarding the fleshy parts of the fruit, the seeds are screened using X-ray to ensure they contain fully developed embryos. Next they are dried, to reduce their moisture content in equilibrium with 15% relative humidity, to remove any free water that would otherwise damage the seed on freezing. Finally, the seeds are stored in containers at minus 20°C, or in some cases minus 40°C. The length of time seeds remain viable under such conditions varies between species, but for 86% of seeds investigated so far, viability is expected to average at least 200 years (Hong, Linington and Ellis, 1996). This is supported by historical evidence (Brewley and Black, 1994) and retest data from Kew’s existing seed bank.

In the future, scientists will be able to remove samples from the seed bank, and reproduce the plant. Seed banks are therefore not purely museums of genetic diversity. Banked seed can be used to reintroduce plants to habitats from which they have been lost. They could also be used in a wide range of sustainable development and scientific research programmes, for example in the search for new medicinal drugs, crops or agricultural pest controls.
Seed banking has much to commend it, in addition to its reliability and simplicity. An estimated 89% of seeds are ‘orthodox’, that is they can tolerate the desiccation process necessary for seed banking techniques (Hong et a/., 1996). Large populations represent most species – a recent study in Berkshire confirmed that 86% of flowering plant species present in the county were represented by over 1000 individuals (R D Smith, pers. comm.). Seed banking also makes use of the fecundity of plants; a single individual Digitalis purpurea (foxglove), for example, produces an average of 78 000 seeds. A relatively large number of seeds can therefore be collected, even from populations of rare plants, without having a significant effect on the future existence of those populations in the wild. Because of their small size, many thousands of seeds can be stored in a relatively small space, ensuring that a high degree of genetic diversity can be conserved for each species at minimal cost.

While conservationists generally prefer in situ conservation methods, in many areas human activities are destroying natural habitats so rapidly that we cannot hope to conserve the plants in situ. In Madagascar, for example, existing forests are under such pressure that it is almost certain that many unique habitats will be destroyed within a few years. As more than 80% of Madagascar’s flora is thought to be endemic (i.e. not found naturally outside the island), some species will undoubtedly be lost before effective in situ conservation measures can be set up.

UK flora
The millennium Seed Bank has two principal aims. The first is to collect and conserve the seed of the entire native UK spermatophyte flora by the year 2000. Three hundred of our 1442 native plants, which regularly set seed, are regarded as threatened with extinction. Among the threats are agricultural ‘improvements’, road building, and drainage and possible climatic change. Kew’s existing seed bank already holds the seeds of some species, for example, the grass Bromus interruptus, which has become extinct in the wild since the seeds were collected. Conserving the country’s entire flora will not only provide a valuable back-up to other conservation efforts, it will hopefully act as an impetus for other nations to follow suit.

Endangered flora of the dry-lands
The second aim of the project is to conserve the seeds of an additional 10% of the world’s flora by the year 2010, in collaboration with overseas countries. The world’s flora is estimated at 242 000 species (Mabberley, 1990), so 10% is 24 200 species in total. The project will concentrate particularly on the dry-lands (arid, semi-arid and sub-humid regions). Far from being dominated solely by unproductive deserts, these areas contain a great deal of biological diversity. They are also experiencing some of the most rapid rates of habitat loss in the world – 74% of the range¬lands of Africa, and 75% of those of Asia, have suffered desertification to some degree (UNEP, 1995). Over one billion people, one fifth of the world’s population, inhabit the dry-lands, a proportion that is expected to rise significantly by the middle of the next century (UNEP, 1992, 1995), and bringing increasing pressures on these fragile marginal habitats.

Another reason for the dry-lands focus is that the seeds of almost all dry-land plants have evolved the ability to withstand drought (and thus desiccation), whereas a significant proportion of plants from humid regions are thought to have seeds that cannot survive desiccation. This ability to remain dormant during drought is spectacularly illustrated by the germination of large numbers and varieties of desert plants after the infrequent rains.
Among the countries that have particularly diverse dry-land floras are Australia, Brazil, Kenya, Madagascar, Mexico, South Africa and the USA. The main phase of the overseas collecting programme is due to start in the year 2000, but seed collecting visits have been made over the last year to Burkina Faso, Jordan, Mexico, South Africa, Tunisia and Yemen.

Why conserve biological diversity?
It is not just environmentalists and scientists who have an interest in preventing the erosion of global biological diversity. The majority of those who live in rural dry-lands in developing countries are utterly dependent on plants for their survival. Wild plants are an essential component of people’s diets, often providing the most important sources of micronutrients and are a vital fallback in times of food shortage (de Waal, 1991). In many dry-land areas, such as the Sahel region of Africa, population growth had out¬stripped increases in agricultural production in recent decades; in Ethiopia, between 1980 and 1988, per capita food production fell by a harrowing 9% (FAO, 1990). Wild plants are therefore likely to become increasingly important as sources of nutrition.

Biological diversity provides for many other everyday needs of people in the dry-lands. Kew’s SEPASAL database (Survey of Economic Plants from Arid and Semi-Arid Lands) records over 6000 species of flowering plants with known uses as foods, fodder, medicines, building materials, insecticides, raw materials for local crafts and industries, and a range of other economic uses (Davis et al., 1996). Obviously, wild plants have a central role to play in sustainable development in the dry-lands.

Biological diversity also benefits people in the developed world. Approximately 25% of the medicines used in the West are derived from plants, as are many pest controls, resins and industrial raw material (Goodin and Northington, 1986). Ironically, 80% or more of the world’s plants have yet to be investigated by scientists for their chemical properties, so we simply do not know the potential benefits of the plants that are being driven to extinction.

Progress to date
The success of the Millennium Seed Bank project hinges on partnership, both within the UK and overseas. Seed collecting in the UK is already underway, with the collaboration of numerous local Wildlife Trusts, statutory conservation bodies such as English Nature and Scottish Natural Heritage, and other scientific bodies. With 817 species collected by Christmas 1997, the task of collecting the UK flora is now over 60% complete. Seed collecting programmes are currently being negotiated with various countries in the tropics and sub-tropics. Under these agreements, local botanists will undertake most of the collecting. Where facilities exist, an agreed proportion (usually half) of the seeds collected will be kept by the country concerned, the remainder being stored at Wakehurst Place.

A world resource
Kew intends to ensure that seeds stored in the Millennium Seed Bank are put to good use. They will be available to scientists throughout the world, subject to the provision of the Convention on Biological Diversity, which calls for agreements to be set up with the host country on access to genetic resources and sharing of any benefits that might arise. Seeds of dry-land species stored in the Millennium Seed Bank are likely to be particularly valuable for such research. Many have adapted chemical defences against insects or unusually harsh climatic or soil conditions, and could therefore contain valuable chemicals or have useful attributes. Other species could be used in environmental restoration programmes; species from the genus Tamarisk, for example, can colonise the unstable soils, and could be used to stabilise sand dunes in severely desertified areas.

The Millennium Seed Bank building is expected to be completed and opened to the general public in the year 2000. It will contain facilities for visiting students and researchers, so that overseas scientists can make use of a full range of research facilities while working on the flora of their country. Much of the research on site will be directed towards establishing optimum seed storage protocols and improving seed collecting techniques. For instance, it may be possible to target future seed collecting activities much more effectively by using Global positioning System (GPS), Geo¬graphical Information Systems (GIS) and genetic information. To date, only 7000 species have had their seed storage behaviour investigated (Smith and Prance, 1997). Research will also focus on problem seeds, such as those of aquatic species and orchids, which are not ideally suited to conventional storage techniques.
The millennium Seed Bank is the ultimate insurance policy against the loss of genetic diversity worldwide. It will not stop the wholesale destruction of natural habitats and populations of flowering species in the wild. However, it will prevent the complete and irreversible loss of much of the world’s genetic diversity, protecting it for the benefit of humanity in the future.

From Biologist (1998)
With acknowledgements and thanks
References available on request.

This year is the 50th anniversary of the founding of the Tree Society, and probably a very good time to gather information in order to compile and record our history.

Please drop us a line, e-mail, or phone with any details that you can remember. Do you have any articles or photographs that we can photocopy or perhaps you have some particular memories or anecdotes worth recording for posterity.

Please give it some thought; we would love to have contributions from all over Zimbabwe.

 

In Retrospect: -WHILE RIVERS RUN

In a ROOTNOTE by Kim Damstra in TREE LIFE No.44 (October 1983):
We are all aware that plants lose water through tiny holes (called stomata) in their leaves. The process is called transpiration. I am always amazed at the volume of water that is lost to the atmosphere in this way. Town planners have successfully drained vleis simply by planting gum trees. We recently learned that the Save River, which has been limited to standing pools for the past months, had begun flowing again, although no rain has fallen. This well-known phenomenon is ascribed to a cold spell a few days earlier, which kills leaves on the hardier of the deciduous trees, stopping transpiration.

The ground water that was lost through the stomata is now available as run-off, and the rivers begin flowing. Along the northern escarpment late-season fires similarly reduce transpiration, and as a result the rivers of Matusadona begin flowing before the summer rains. A remarkable phenomenon, indeed.

[Comment 2000: This phenomenon was recorded from the Bembezi River, northwest of Bulawayo, following a severe frost in the late 1940s. A staff member of the Forestry Department had dossed down for the night in the dry bed of the Bembezi in August or September, and woke in the early hours of the morning with water swirling around him! No rain had fallen anywhere in the catchment of the Bembezi.]

-Lyn Mullin. In Retrospect will be continued

Please continue collecting seeds for Ann Bianchi. In particular she needs seeds of Heteropyxis dehniae, Sterculia rogersii and Croton pseudopulchellus.

 

ANDY MACNAUGHTAN   CHAIRMAN