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Lets Atlas out Alien Proteaceae too!

RESEARCH PROGRESS

LETS ATLAS OUR ALIEN PROTEACEAE TOO!

Dave Richardson, Jonkershoek Forestry Research Centre, Stellenbosch

The Proteaceae Atlas Project provides an exciting opportunity for everyone to get to know the wealth of our indigenous Proteaceae. But let's not forget the Australian cousins of our splendid clan - both those that already made the Cape their second home and those that have put down their roots but have not (yet?) spread. There is a lot to be learnt about our own proteas by comparing them with those from "down under".

The Proteaceae family is concentrated in temperate Australia (about 700 species) and in the Cape (about 350 species). The family is particularly prominent in fire-prone shrublands of the two regions. Proteaceae shrubs are usually the dominant woody plants on most nutrient-poor soils in both regions: Protea, Leucadendron and Leucospermum are prominent in the Cape, whereas Banksia and Hakea are conspicuous in Australia. Although no genera are shared, many fynbos areas have been invaded by Hakea - often to the point that indigenous species are eliminated. Although you may not feel kindly disposed to these Australian immigrants, they clearly deserve attention from atlassers, for many reasons.

Firstly, let me introduce you to these foreigners and tell you something about their travels in the Cape. Three species of Hakea (Needlebushes or Hakeas) are proclaimed noxious weeds in South Africa. The most noxious of these is H. sericea Silky Needlebush, an erect 2 to 3m tall (occ. to 5m) shrub with dark green, needle-like leaves (ask anyone who has helped in a hack) up to 40 mm long, 1 mm diam. and hairless. Hakea gibbosa Rock Needlebush is similar to H. sericea in general appearance, but the leaves are longer (40-50 mm), stouter, and covered with short hairs. The other invasive alien, H. suaveolens Sweet Needlebush is very different: it has hairless, 70-100 mm long leaves that are divided into few or many upright needles. The Silky Needlebush is by far the most widespread of the three and is to be found in Fynbos on most mountains from the Cape Peninsula to Grahamstown. Rock and Sweet Needlebush have much smaller ranges, but may be very conspicuous in some areas (e.g. the Cape Peninsula). We would dearly love to know exactly where these species occur, so please note them when they occur in your Record Localities.

A fourth species, H. salicifolia, HEDGE Needlebush is a very popular hedge plant. Because it is not as weedy as its relatives, it is known as the "Mak Hakea" in Afrikaans. It does not spread from hedges into natural fynbos or forest, but, in my experience, invades only highly disturbed areas such as road verges. But don't take my word for this - please check it out!

An important characteristic of all Needlebushes, and one that has helped the successful ones immensely in their quest for dominance of our indigenous vegetation, is the fruit: a woody "nut", termed a follicle, which contains two winged seeds. Inside the follicles the seeds are protected both against predation and the heat of fires. The follicles accumulate on the plants and when the plants die (they have thin bark and are easily killed by fire) the follicles open and release the winged seeds onto the landscape. Some of the seeds are carried great distances by wind, but most seeds fall close to the parent plant. This gives rise to a two-pronged process of invasion: seeds falling nearby form dense stands and those dispersed far (by wind) establish new infestations which in turn become dense thickets after fire. This invasion began soon after Needlebushes were introduced to the Cape around 1840. Silky Hakea spread rapidly from a few planted sites. The atlas data will help us determine how fast Hakeas can spread, and whether they are still spreading to new areas. This will allow us to determine the limits of the distribution ranges of the species.

Great progress has been made in the control of Needlebushes in the Cape. Mechanical control has been used since the early 1970s. Those of you who have hacked know the procedure. First, the plants are chopped down and then left lying in the veld. This allows the follicles to open and release the seeds. These seeds are eaten by birds and rodents, but because of their large numbers many survive. Spring felling is best, as this exposes the seeds to predation throughout summer and autumn - until the first heavy rains induce germination. Some 12-18 months after felling the veld is burned and all the young plants are killed before they have a chance to produce more seeds. This method is very effective, and works just as efficiently with pines. However, some plants always survive and the felling operation is very expensive: unless regular follow-up operations are undertaken the area can revert to a dense Hakea stand after the following fire. Also where dense stands occur the intense heat produced by burning the dead Hakeas may destroy the Fynbos seed banks, kill the roots of resprouters, and alter the physical properties of the soil: the result is a barren landscape that must be planted.

However, the key to the invasion of the Needlebushes is the vast amount of seeds produced: in Australia the same species produce relatively few seeds. Why? In Australia the vast majority of seed are eaten by insects, which are specialized to get through the protective follicles. Three of these seed-attacking insects have been released in South Africa. One of these, Erytenna consputa Hakea Fruit Weevil is capable of destroying 80% of seeds. It is already reducing the spread of Needlebushes and reducing the density of stands. You can easily observe the shrivelled follicles caused by the weevil: look closely at one and you will find the exit hole through which the larva escaped before pupating to adulthood. Note that the weevils can only enter young follicles: mature follicles are too heavily protected. So for the meantime we cannot dispense with mechanical clearing.

We were not alone in discovering that Needlebushes where taking over Fynbos. An indigenous fungus Colletotrichum gloeosporioides discovered this ideal food-source in the 1960's. The symptoms of fungal attack are the development of cankers on the stem and branches (usually oozing gum). This kills the bark and dieback of the leaves - or the entire plant - above the infection follows. Patches of dead Needlebushes can be seen in all parts of the range of the Silky Needlebush, which is most susceptible to this fungus. However, the fungus is temperamental and requires specific weather conditions to spread.

Once the Hakea invasion has been controlled, we must start conserving Needlebushes in our nature reserves. This is the only way we can ensure that the weevils and fungus will always be there to prevent future invasions.

Atlassers can help us to monitor the success of these control measures by collecting data on the distribution and densities of Needlebushes (just treat them as Proteaceae species in the Proteaceae Present Box). If you are particularly keen you may note (in the Additional Comments Box) the incidence of weevils, the proportion of follicles killed, or the proportion of plants infected or killed by the fungus.

What about the other Australian genera of the Proteaceae planted in the Cape? Atlassers should certainly be on the look-out for new invaders. Several species of Banksia have been planted on a fairly large scale in the western Cape for the cut-flower market. Some species share with the pest Needlebushes a set of features (viz. woody follicles that protect and store the seeds until after a fire) which suggest that they may also invade Fynbos. These species have only recently been widely planted - perhaps they are just waiting in the wings for the right moment to kick off in the scramble for dominance of the Fynbos. Far-fetched? I wonder whether it crossed anybody's mind in 1840 that Hakea sericea might become a major weed. With your help we may be able to nip these invasions "in the bud", thus preventing the destruction of our natural vegetation and saving the expense of the costly control measures required to eradicate the aliens.

Meanings of scientific names: 6. Hakea.

Hakea (after Baron CL von Hake (1745-1818), patron of botany)

gibbosa: hunched (follicle)

salicifolia: willow-leaf sericea: silky (leaves)

saligna: willow-like (leaves) acicularis: awl-like (leaves)

suaveolens: sweet-smelling (flowers) tenuifolia: narrow-leaf

Copies of an information pamphlet on the Hakea species (Pamphlet 365/7: Plant Invaders) are available from the Department of Environment Affairs, PRETORIA 0001, or directly from Dave at: Jonkershoek Forestry Research centre, Private Bag X5011, STELLENBOSCH 7600.

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