By Geoff Tribe
Australia’s gift to the world was the gum- or Eucalyptus tree now found growing throughout the world where it has been planted for its timber, fire-wood, honey resource and as an ornamental. In southern Africa, eucalypt plantations not only provide hardwood timber and half the paper-pulp needs of the region, but are also found scattered throughout the landscape. Almost everywhere there was European habitation in the past and present, the ubiquitous eucalypt is bound to have been planted. At most wind pumps in the arid Karoo or the Kalahari Desert, a few eucalypts may be found growing nearby as a source of shade for the stock.
Origins of Eucalyptus in South Africa
South Africa is poorly endowed with natural forests, with only 0.3% of the land area afforested. Exploitation of these indigenous forests began with European settlement at the Cape of Good Hope in 1652 and gradually extended eastwards as the local resources became exhausted. Timber was required for shipbuilding, housing, ox-wagons, furniture and fuel. The early Cape governors realized the necessity for the importation of fast-growing exotic tree species and the first introductions were the common oak (Quercus robur) followed by cluster and stone pines (Pinus pinaster and Pinus pinea). By 1847, attempts were made to halt the exploitation and conserve what remained of the indigenous forests by restricting access. Increased demand for timber arose in the 1870s for railway sleepers, telegraph poles and props for mines. The first timber plantations consisting of eucalypts was established at Worcester in 1876 to provide firewood for railway locomotives. However, it was only during World War II when timber imports were disrupted and prices escalated that a boom in afforestation began and continued after the war with a total area of commercial plantations in South Africa now exceeding 1.5 million hectares, of which slightly less than half is under eucalypts.
Much of South Africa’s honey production relies on the nectar from these eucalypt plantations and woodlots throughout the country. Commercial eucalypt plantations, however, are not found in the Western Cape, but a variety of spectacular flowering gums have been planted as ornamentals (Fig. 1a,b,c,d). Many of these originate in the winter rainfall region of Western Australia and so are well adapted to the climate of the Cape. These exotic trees are able to grow rapidly and are able to outperform those in their country of origin because they are not subjected to the depredations of the many pests and diseases that afflict them in their natural environment.
Cape Town ornamental gums
The most striking of the Christmas flowering gums is the Red-flowering gum, Corymbia (Eucalyptus) ficifolia (Fig.2) which is extremely attractive to honeybees (Fig. 3) and many other insect species. There are colour varieties from a deep crimson to almost orange (Fig.4a,b,c,d,e,f) and some may be hybrids between the White-flowering gum, Corymbia calophylla (Fig. 5) as seen in the red tinges (Fig. 6). The profusion of clumped flowers is available to bees over a period of several weeks. Both nectar and pollen are produced in abundance and the honey of the red-flowering gum is distinctive in that, when the honey is extracted or a comb broken, the honey forms long ‘strings’. Another spectacular tree which flowers in late autumn is the swamp messmate Eucalyptus robusta (Fig.7).
Also flowering around Christmas and into the next year is the prime honey producer of the Western Cape, the Sugar-gum, Eucalyptus cladocalyx (Fig.8). The sugar-gum grows to impressive heights and is possibly the most important gum in the Western Cape because it tides the bees over the crucial dearth period of January-March when not much forage is available in the indigenous fynbos and temperatures soar to 35°C. It also produces the premium honey in the Western Cape – a honey which may take 10 years or more to crystalize if from pure source. All Eucalyptus species in the winter rainfall areas contribute to the wellbeing of the honeybees and thus safeguard the fundamental economy of the region.
There are many other less spectacular species of eucalypts growing in Cape Town and surroundings because many species were introduced into the Arboretum at Tokai during the early days of the Commonwealth in order to select those which showed promise as plantation species. The following list is of some of these species and their rating in nectar and pollen production out of a maximum of 4 according to Johannsmeier (2001):
Nectar Pollen Months Origin
Eucalyptus ficifolia* 3 2 12-2 WA (south-western)
Eucalyptus calophylla* 3 2 12-5 WA (south-western)
Eucalyptus cladocalyx 4 1 1-2 South Australia
Eucalyptus lehmannii** 3 2 9-11 WA (south-western)
Eucalyptus diversicolor 3 2 2-3 WA (south-western)
Eucalyptus globulus 2 2 7-10 Tasmania
Eucalyptus gomphocephala 3 4 3-4 WA (south-western)
Eucalyptus robusta 3 3 4-6 NSW + Queensland
Eucalyptus leucoxylon 3 1 5-9 South Australia
*Genus of blood-woods and ghost-gums recently reclassified as Corymbia.
**Species present in South Africa now confirmed as Eucalyptus conferruminata.
Features of eucalypts
Most eucalypt species carry three sets of reproductive stages – the ‘fruits’ (seeds) of the previous year, those presently in flower and the buds beginning to form for the following year. It usually takes a full year for the buds to mature and thus the weather conditions of the previous year have a direct effect on the number and profusion of flowers in the present year. Initially drought conditions may stimulate the tree to produce more buds as opposed to new growth, and a bumper honey flow may be experienced following this. But if the drought persists for several years, then the tree ceases both growth and bud formation. This curtailing of both growth and bud formation may also be induced by the action of pests.
The arrival of the Eucalyptus tortoise beetle (Trachymela tincticollis) in the Western Cape which severely defoliated all concolorous (similar shade of colour on both sides of the leaf) eucalypt species caused the trees to die back and as a result, also stopped the formation of buds. The introduction of the egg parasitoid, Enoggera reticulata resulted in a 96% parasitism rate (Tribe and Cillié, 2000) which was subsequently followed by a massive flowering of Eucalyptus gomphocephala trees, the weight of the flowers causing several branches to break.
Many insect pests of eucalypts that have arrived in South Africa have had a devastating effect on the monospecific and contiguous plantations. The success of Enoggera reticulata in controlling the eucalyptus tortoise beetle was largely due to the exclusion of its two hyper-parasite species which together accounted for 88% of its population in Australia. Freed from its own parasitism, it was most effective in parasitizing the eggs of its primary host and preventing the emergence of the highly destructive larval stage.
Eucalypts in Australia
Honeybees were absent in Australia until introduced by European settlers and before then eucalypts were pollinated exclusively by a host of indigenous insects, birds and mammals such as possums. Their exposed flowers which gave easy access of their pollen and nectar to a wide variety of organisms attest to this. Although most flowers of eucalypt species are white to cream coloured and therefore more attractive to insects, red flowering gums (presumably more attractive to birds) also attract honeybees and many other insects. Perhaps the primary reason for this unusual attraction to red flowers is the incredible melliferous scent emanating from the eucalypts when in full flower.
The amount of nectar secreted by eucalypts is immense. In Yuraygir National Park in northern New South Wales it was possible in the mornings to gently move the sand away from under where a cluster of flowers had dripped over-night, leaving a loosely nectar-bound core of sand the size of a small bucket. Honeybees were excluded from the park due to the controversy raging at that time on the possible negative effect of alien honeybees on indigenous pollinators.
Eucalypts as ‘invaders’
Several Eucalyptus species have been placed on the invasive list of the Department of Agriculture including the River red-gum, Eucalyptus camaldulensis, whose seeds are discharged into water courses and add to the many other exotic species clogging the rivers. However, it is not common to see a myriad seedlings sprouting around established eucalypts. This is mainly a consequence of the fire-ecology of natural eucalypt forests in Australia. When visiting the endemic Ludlow Tuart Forest (Eucalyptus gomphocephala) south of Perth, one is struck by the non-random distribution of the trees – as if they had been planted in rows. The reason for this is that after a fire progresses through the forest and burns fallen trees, dehiscence occurs and seeds falling into the ash germinate and grow. Because the ash occurs in strips, this results in rows of seedlings following the outline of the burnt trunks. Apparently without this ash few seeds would germinate and eventually grow to maturity. This phenomenon is utilized by foresters where, following the felling of sections of mature natural forests, seeds are collected from the now open capsules of felled trees and then temporarily stored. The logs are removed and the debris is then burned and soon thereafter the stored seeds are spread over the area by helicopter into the ash for successful germination.
In paddocks bordered by eucalypt windbreaks such as E. lehmannii (now identified as E. conferruminata) (Fig.9) few if any seedlings survive as they are eaten by antelope, sheep, goats and cattle and therefore pose no danger of spreading.
Other attributes of eucalypts
Eucalyptus species such as the white stemmed Corymbia (Eucalyptus) papuana ghost gum of the outback growing in their natural environment are aesthetically beautiful. The texture and colour of the bark is a reflection of the habitat in which they occur and can also add to their beauty as ornamentals as in suburbs of Cape Town. Stringybark species are water and fire resistant and grow in regions inundated with water for months of the year followed by fires. White stems resulting from peeling bark reflect sunlight, an adaptation to fierce heat (much like kokerbooms, Aloe dichotoma now Aloidendron dichotomum in arid areas of southern Africa). Dwarf, multi-stemmed mallee eucalypt species in fire prone areas of Australia rely on an underground woody rootstock (lignotuber) in order to re-sprout after the fire has passed through. The blood-woods if wounded ooze a red resin which is dried and powdered and used as medicine (Fig. 10).
Eucalypts as integral to the proliferation of honeybee colonies in the Western Cape
Not only are the eucalypt species in the Western Cape highly attractive as ornamentals, but are essential to the wellbeing of honeybee colonies and thus to the agricultural base of the economy of the region. Does the presence of alien eucalypts distort or negatively influence the survival of the Cape Bee and other pollinators from flies to beetles and birds which visit them? Available evidence shows that eucalypts are in fact possibly responsible for an increased number of colonies in the region due to an increased amount of nectar and pollen. Such healthy honeybee colonies are able to produce a greater number of reproductive swarms each year than would have occurred naturally in the fynbos, and so maintain or increase the natural capacity of the area.
The author at work:
Boland D.J., Brooker M.I.H., Chippendale G.M., Hall N., Hyland B.P.M., Johnston R.D., Kleinig D.A. and Turner, J.D. 1987. Forest Trees of Australia. CSIRO, Australia. 687pp.
Johannsmeier, M.F. (Ed.). 2001. Beekeeping in South Africa. Plant Protection Research Institute Handbook No 14, Agricultural Research Council of South Africa, Third Edition, Revised.288pp.
Tribe, G.D. and Cillié, J.J. 2000. Biological control of the Eucalyptus-defoliating Australian tortoise beetle Trachymela tincticollis (Blackburn) (Chrysomelidae: Chrysomelini: Paropsina) in South Africa by the egg parasitoid Enoggera reticulata Naumann (Hymenoptera: Pteromalidae: Asaphinae). African Entomology 8(1): 15-22.