Boomplantweek en die Internasionale Jaar van Woude - Dendro.co.za

DENDRON » No/Nr: 43 » November 2011
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UNDERGROUND TREES OF THE PONDOLAND CENTRE
plane), occur widely as forest trees but also can be
found as chasmophytes (growing in fire-protected
rock crevices) in and around rock exposures in
the grasslands, often near forests. Under these
conditions, the aerial parts are burnt off regularly,
but I have not seen an indication of reversion to the
arborescent state in places where fire has missed
out a year or two. It would be informative to study
the genetics of the two forms of these species to see
whether they are either facultative geosuffs or, just
possibly, evolving towards the obligate state. The
other possibility would be to take seed of each form
for growing on, but as the transition from one form
to the other may be incomplete, seeds could also
be in a stage of transition and reproduce either way.
The age of plants has always been
a fascination...it is becoming clear
the we have a tencency to seriously
underestimate it.
Looking at the occurrence of geosuffs in the
Pondoland Centre, temperatures are moderate;
dry periods, especially in winter, can occur but
droughts are rare; geosuffs occur on both the
shallower sandstone derived soil of the Msikaba
Formation and on deeper dune sands; herbivory is
a constant; fire is also a constant in our grasslands
(Abbott, PlantLife 35) and the soils are nutrient poor
because of the high rainfall.
Meg Coates Palgrave (PlantLife 18) is convinced
that the success of seedlings in the indigenous
woodlands (‘miombos’) of Zimbabwe is an
infrequent occurrence and suggests that there,
trees normally reproduce vegetatively from
existing rootstocks. This provides an example of the
ancestral ability of woody plants to produce coppice
shoots but still leaves the reasons for adopting the
geosuff growth form (as opposed to a proper tree)
unexplained. In contrast to Meg’s findings in the
Zimbabwe woodlands, our forest species down here
seem to do quite well in setting seed and generating
seedlings although some species certainly flower
irregularly. Even coppicing forest species such as
Dahlgrenodendron natalense (Sandstone quince)
set fertile seed from time to time. Another such tree
is the rare Lydenburgia abbottii (Pondo bushmans
tea) which I have seen with a mass of seedlings
below it.
Compared to our forest regeneration, Pondoland
grasslands appear to depend largely on perennial
species which shoot at ground level or below, socalled
resprouters. The number of herbaceous plant
species which exist as clones is large and as Acocks
(1975) tells us “The Pondoland Plateau Sourveld
is the densest veld in the Republic, so dense that
grasses grow as single shoots rather than as tufts;
at least the tufts are very small.” Thus it seems likely
that seedlings would find it harder to establish
amongst resprouters and tufted species.
The range of selective pressures suggested to
promote the geosuff growth form is quite large,
but the wide range of distribution and conditions
of geosuff occurrence suggests to me that the
pressures of fire and herbivory are indeed
candidates for such a change of behaviour, at least
in the Pondoland Centre. These could well be acting
in concert with some or all of the other factors put
forward. Here, I would suggest the opportunity
offered by forest margin ecotones with grassland
could well be a potential nursery school for the
evolution of geoxylic suffrutices from arborescent
forest forms.
The age of plants has always been a fascination to me
and it is becoming clear that we have had a tendency
to seriously underestimate it. According to a popular
website that, amongst others provides information
on botanical record breakers (waynesword.
palomar.edu accessed 14 April 2008) there is a
shrub in the Mojave Desert called creosote bush,
Larrea tridentata (Zygophyllaceae). The original
stem produces a series of aerial branches but as the
centre of the stem dies off, the remaining portions
continue to grow as a large ring of peripheral shoots;
a growth pattern reminiscent of that in a geosuff,
except that in the case of creosote bush the clone
forms an ever-widening circle surrounding a central
barren area. The oldest of these clones is estimated
to be about 12 000 years old. Another clonal plant,
Lomatia tasmanica (Proteaceae) in Tasmania, may
be one of the oldest plant clones in the world. Known
as the King’s Holly, the species appears to be a
sterile triploid incapable of producing viable seeds
and the existing clones are estimated to be as much
as 43 000 years old! With examples such as these,
we should not be shy to suggest considerable ages
for our geosuffs. There is an extensive clonal colony
of Eugenia capensis subsp. gueinzii (Coast myrtle)
in grassland on the ancient Berea Formation sand
dunes along the Wild Coast which is about 50 x 30
m in extent. No doubt this particular clone must be
many hundreds, if not thousands of years old. This
evidence of long term stability is a very important
consideration when developments are proposed
which can destroy our grasslands. In fact, this
particular colony of Eugenia capesis subsp. gueinzii
(Coast myrtle) grows on dunes earmarked for the
possible mining of heavy minerals. Suggestions
of rehabilitation or revegetation, often mentioned
in environmental assessments, seem rather
presumptuous. It is quite clear that the prefix “re-”
is out of place and all that can happen to grassland
which has been destroyed by development, is the
introduction of plants to provide a covering to the soil
without a hope of restoring the earlier ecosystem.
Anisha Dayaram of Wits University is currently
working on carbon dating some geosuffs in
collaboration with Custodians of Rare and
Endangered Wildflowers (CREW). There is so little
known about the underground parts of plants in
grasslands and I am delighted that Anisha has taken
on this project and I sincerely hope that it will lead
to other investigations into the behaviour of more of
these plants.
Marita Thornhill and Ian Felton (PlantLife 23) feel
that the term “woody grasslands” better describes
the coastal grasslands of Maputaland with their
abundant of geosuffs. Perhaps we should give
thought to changing our terminology for the
Pondoland veld to give recognition to the fact that,
UNDERGROUND TREES OF THE PONDOLAND CENTRE
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although individual numbers of grasses exceed all
other kinds of plant in our ‘grasslands’, they are far
the least in species numbers and biomass. Cryptic
Savanna or Dwarf Open Woodland perhaps, but
certainly something which gives better recognition
to the plant assemblage.
References:
1. Abbott, A.T.D. 2006. Where do our beautiful
2.
grasslands come from? PlantLife 35: 3–6.
Burtt Davy, J. 1922. The suffrutescent habit as an adaptation
to environment. Journal of Ecology 10: 211–219.
3. Acocks, J.P.H., 1975. Veld types of South Africa. Botanical
Research Institute, Pretoria.
4. Coates Palgrave, M. 1988. Regeneration of indigenous
woodland in Zimbabwe. PlantLife 18: 30–32.
5. Gunn, M. & Codd, L.E. 1981. Botanical exploration of
southern Africa. B.R.I. A.A.Balkema, Cape Town.
6. Jackson, B. Daydon, 1971. A glossary of botanic terms.
Hafner Publishing, New York.
7. Thornhill, M. & Felton, I. 2000. The underground forests of
Maputaland. PlantLife 23: 9–10.
8. Stearn, W., 1983. Botanical Latin. David & Charles, London.
9. Steenkamp, Y., Kellerman, M.J.S. & Van Wyk, A.E. 2001. Fire,
frost, waterlogged soil or something else: what selected for
the geoxylic suffrutex growth form in Africa? PlantLife 25: 4–6.
10. White, F. 1976. The underground forests of Africa: a
preliminary review. Gardens’ Bulletin, Singapore 29: 55–71.
Virtual Tree Herbarium (ViTH)
Adapted from news items distributed by the University of Johannesburg & Naas Grové
The University of Johannesburg, under the auspices
of Prof Michelle van der Bank and Dr. Oliver Maurin,
is busy developing a Virtual Tree Herbarium (ViTH)
based on the same concept as similar projects for
birds, mammals and other organisms with the Bird
Atlas and Virtual Museum. The general idea is to have
a system available to anyone, to capture tree / shrub
observations from the field. This idea appealed to
the Central Committee of the Dendrological Society
as it has proven to be very successful with projects
such as the Bird Atlas. It is a non-profit initiative
that would allow our members from all branches
to contribute towards the development of more
accurate species distributions maps, and thus
contribute towards science.
The data that would be uploaded by the members
of the Society on the system will only involve
observations and must contain: 1) A Temporary
identification 2)A GPS location and 3) A set of
photographs of the tree, leaves, bark and any other
features such as fruit and flowers (to help confirm
the identification).
A panel of experts then has to screen, evaluate and
verify all submissions at intervals and record those
which can be verified. The verified data would
eventually serve as the basis for an accurate map
and database of tree / shrub species found in all
parts of the country.
The Dendrological Society held a workshop
facilitated by Dr. Oliver Maurin and Professor
Michelle van der Bank on 30 July 2011 at the
University of Johannesburg to discuss the project
and ways to participate. The following members
attended the workshop: Gert Middelberg, Fanie de
Meillon, Izak van der Merwe, Naas Grové, Christoph
Fuhrmann and Walter Barker (Tree Society of South
Africa)
An experimental survey of 33 tree species was
made in Melville Koppies on 15 October 2011 by
the Magalies branch of the Society during an outing
with the botany Masters Student Mr Phillip Rousseau
of the University of Johannesburg, and these were
the first entries to be submitted by the Society on the
ViTH system. Members who wish to contribute to the
project can consult our website for more information
at www.dendro.co.za
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DENDRON » No/Nr: 43 » November 2011