The alien flora of the Cape of Good Hope Nature Reserve

An annotated species list of the alien vascular plant flora of the Cape of Good Hope Nature Reserve is presented. The flora comprises five gymnosperm and 68 angiosperm species that are definitely alien to the reserve and four angiosperm species that are possibly alien. The life-form distribution of the alien flora is shown to be significantly different from that of the indigenous flora; trees, shrubs and annual herbs are more important in the alien flora, and dwarf shrubs and perennial herbs are much less important. Biotic factors are suggested as being important in determining the success of alien invasions, in particular grazing by ungulates. The invasion rate is currently about one new species per year. By ceasing to introduce tree species and by restricting human disturbance, the rate of invasion of new species could be reduced. of biotiese faktore, veral beweiding deur hoefdiere, 'n belangrike rol kan speel by die indringing van uitheemse plante. Tans word die tempo van indringing op ongeveer een nuwe spesie per jaar geskat. Deur die invoer van boomsoorte te staak en versteuring deur mense te beperk, kan die indringingstempo van nuwe plantsoorte verminder word.


Introduction
The invasion of natural vegetation by alien plants constitutes one of the Cape of Good Hope Nature Reserve's major management problems (Taylor 1977;Taylor eta/. 1985;Clark 1985). In this paper we list for the first time all the species involved, providing details of their history, distribution and status in the reserve, and present some analyses of the problem, based on this information.
The reserve is located at the southern tip of the Cape Peninsula (34° 12'S 18°22'£), is 7750 ha in extent, ranges in altitude from 0 to 366 m.a.s.l. and experiences mean annual rainfall ranging from 300 to 700 mm. The geology, ecology and history of the reserve have been described by Opie (1967) and Taylor (1969). The vegetation and flora of the reserve have been documented by Taylor (1984a, b;. The vegetation is primarily mountain fynbos on the central plateau which is underlain by Table Mountain sandstone, with strandveld vegetation on the littoral shelf which is widest on the western side of the Peninsula.

Methods
In order to compile this list the alien species (Wells et at. 1986) were extracted from the published flora of the reserve (Taylor 1985). Additional species were obtained from the published accounts of alien plant invasions of the reserve (Taylor et at. 1985) and from the unpublished observations of the authors. These species were annotated using the conventions of Wells et at. (1986), the data provided by this text being supplemented where necessary from a range of botanical reference books. Details of each species' distribution and status within the reserve were based on field observations of the authors, supplemented by data recorded by H.C. Taylor in his card index of the area's flora and in the raw data and field notes from the fixed-plot surveys (Taylor et a!. 1985). Only alien plant species that are known to have self-seeded on the reserve are included. Species that are known to invade areas of natural vegetation within the reserve are asterisked (*). Species that are or have been a major problem in the reserve are given a double asterisk (**) . Species were defined as constituting a 'major problem' when they have been observed to form dense stands in areas of natural vegetation. These stands tend to exclude the native flora and have generally required active control measures to prevent their spread. Those species which are not undoubtedly alien to the reserve are bracketed.
The term 'disturbed' is used throughout this paper to refer to anthropogenic disturbance. Within the reserve this mainly takes the form of soil disturbance arising from road building activities and that around picnic sites and human habitation. The clearance of dense stands of alien trees is also considered to give rise to 'disturbed' areas. Prior to the reserve's proclamation, certain areas were cultivated. These are also termed 'disturbed' .
A map giving the location of most of the places named in the present account and the location of the permanently marked alien plant-monitoring plots (numbered 1 to 100) is presented as Figure 1 of  and Taylor et a!. (1985).
In the list that follows, collections are given by the name of the collector followed by the collector's number. In the case of collections by H.C. Taylor these are given in the form (T2355). All the Taylor collections are lodged with STE and the other collections cited are either in NBT or BOL. Herb, annual from ?Europe. This small grass has been recorded from the hills between Ribboksdam and Platboom in the south of the reserve by Taylor (T5282) . * Ammophila arenaria (L.) Link.

The alien flora
Marram grass. Herb, perennial from Europe. Growing on dunes north of Die Mood where it had probably been planted in a dune ' reclamation' campaign. Not considered to be spreading in the reserve .
Wild oats. Herb, annual from Europe & Asia. Widespread in reserve but is mainly confined to disturbed areas such as road verges, old lands and around present and old homesteads and picnic sites. Does not generally invade natural veld. Very palatable and is probably being kept in check by grazers. In areas of 100% alien tree cover that were cleared in 1986, dense stands of A. barbata have germinated. These areas were apparently cultivated at some time in the past.
Kikuyu. Herb, perennial, East Africa. Found mainly at Klaasjagersberg, Perdekloof, the Homestead Restaurant and at picnic sites. Spreads in wet areas and outcompetes indigenous species. Isolated patches are scattered around the reserve, often where lawn cuttings have been dumped or used in erosion-control operations. This species is currently heavily grazed in the reserve. * Vulpia myuros (L.) C.C. Gmel.
Matsedge. Herb, perennial, elsewhere in South Africa. A few small clumps occur in the Klaasjagersberg river near the offices and a large stand in the lower reaches of this river near Die Mond. Also occurs in the marsh at Olifantsbos. This species has been cultivated in ornamental ponds at Klaasjagersberg and was not included in the reserve's flora by Taylor (1985). If this species is indeed alien to the reserve it could pose a significant conservation problem in the future.] Arecaceae * Phoenix dactylifera L.

Ornithopus sativus Brot.
Seradella. Herb, annual, Europe & Asia. This species was introduced to the reserve as a fodder legume in the Circular Drive area. These plantings were initiated in 1959 in order to improve the reserve's grazing for large ungulates (Opie 1967). The introductions of forage legumes all failed as a result of over-utilization by these ungulates (Opie 1967;Millar 1970). Apparently this species is now no longer present on the reserve. * Sesbania punicea (Cav.) Benth.
Red sesbania. Shrub, perennial, South America. One stand of this species was discovered in the reserve in the early 1980s. The plants are growing on a borrow pit adjacent to the main road near Plot 58. The patch is approximately 500 m 2 in area. Clearing every second year has not proven successful so annual clearing is now being undertaken.  -Afr. Tydskr. Plantk., 1987, 53(5) Solanum nigrum L. Scop.
Nightshade. Herb, variable, origin uncertain, thought to be alien to South Africa. This species is found in disturbed areas around old human habitations and in old cultivated fields. Orobanchaceae * Orobanche ramosa L.
Blue broornrape. Herb, root parasite, annual, Europe & Asia. One patch found at gate at Scarborough in 1986 growing near the coast in sandy soil. Also present near beaches and at Cape Point next to footpath near the lookout spots. Myoporaceae * Myoporum serratum R.Br.
Manitoka. Tree/shrub, perennial, Australia. This is a coastal species which occurs in the dunes at the Homestead Restaurant, Olifantsbos and Die Mond. Also found at Black Rocks. Numerous seedlings come up after clearing Acacia cyclops in these areas.
Occurs mainly on roadverges and other disturbed sites in the reserve.
Horseweed fleabane. Herb, annual, North America. Grows on roadverges and along gravel tracks. Common around buildings.
Hairy wild lettuce. Herb, perennial, Europe & Asia. As for Plantago lanceolata but also recorded in the Gifkommetjie turn-off plot in October 1971.
As for P. lanceolata but also recorded on the western shore of Sirkelsvlei in September 1972.

Discussion
The naturalized alien vascular plant flora of the Cape of Good Hope Nature Reserve comprises 5 species belonging to the Gymnospermae and 68 definitely alien species belonging to the Angiospermae. An additional four angiosperms are possibly alien to the reserve. Of the 19 definitely alien monocotyledonous species seven are not known to grow in areas of natural vegetation, being confined to areas of intense human disturbance such as picnic sites. None of the monocotyledons were considered to be posing major problems in the reserve whereas one gymnosperm and six dicotyledons were. All of these were trees.
The life-form distribution of the alien flora is markedly different from that of the reserve's indigenous flora (Table 1).
Even when we combined all tree and shrub categories (but not dwarf shrubs which are distinctive, being defmed as species never exceeding I m in height), the shrub/climbers with the climbers, and the biennial and variable herbs with the annual herbs, the Chi-squared test for heterogeneity of the indigenous and alien flora distributions was highly significant (X 2 5nF = 113, p < 0,001). Tree and tree/shrub species are much more frequent in the alien flora whereas the shrub and dwarf shrub element, which dominates the indigenous flora, is almost totally absent from the alien flora. These results are in accord with the general observation that alien trees appear to have filled an 'empty niche' in the fynbos (Campbell et al. 1979;Mollet al. 1980;Macdonald 1984). Comparison of ecosystems in matched environments in the Mediterranean-type regions of Australia (whence 18 of the reserve's invasive tree and shrub species emanated) and South Africa, has identified the absence of tall trees in the fynbos as one of the important anomalies requiring explanation (Milewski & Cowling 1985). That all six of the angiosperm tree species causing major problems in the reserve are from Australia reinforces the contention that this continent has given rise to a suite of tree species especially well adapted to invading fynbos vegetation (Macdonald 1985).
The other life form which is much more frequent in the alien flora than in the indigenous flora is that of the annual herbs (Table 1). However, of the 29 definitely alien annuals, 10 are apparently confined to sites of intense human disturbance. Most of the remainder occur most commonly in such sites. These species are found in natural vegetation only where this is very open, e.g. Briza minor on stream banks, Medicago polymorpha on the edge of Sirkelsvlei, and Melilotus indica next to the sea and on the rocky hills near Ribboksdam. Raitt (1983) has shown that where fynbos is subjected to a long history of frequent and intense human disturbance, the alien flora is totally dominated by this life form (690Jo of introduced genera being annuals alongside a railway on the Cape Flats).
It is also of note that 24 of the 29 naturalized annuals originate from Europe and Asia, many of them from the Mediterranean Basin. The ability of plants from this region to invade areas of human disturbance in the relatively recently colonized Mediterranean-type regions of the world has been attributed to the long history of human disturbance that the Mediterranean Basin has experienced (Groves 1986).
Small perennial plants are only a minor component of the reserve's alien flora. The few dwarf shrubs and perennial herbs that have successfully invaded within the reserve are, like the annuals, almost entirely restricted to sites of human disturbance. Where they are present in fynbos they are once again found in areas of relatively open plant canopies, e.g. Ammophila arenaria on littoral dunes and Spergularia media on rocky littoral sites. The inability of low-growing alien plants to successfully invade fynbos within the reserve is in accord with the hypothesis that there is intense competition for light between alien and native species in fynbos communities (Macdonald & Richardson 1986 Another factor that might be limiting successful invasion by plants of these growth forms is herbivory. Several herbaceous alien species have been observed to be heavily grazed by ungulates within the reserve, e.g. A vena barbata, Cortaderia selloana and Pennisetum clandestinum. The intentional introduction of forage legumes and pasture grasses to ploughed strips along the reserve's roads in the late 1950s and 1960s failed, at least partly, as a result of excessive defolation of the young plants (Opie 1967;Millar 1970). Grazing has been suggested to be an important selective pressure in shaping the alien flora of southern Africa (Macdonald 1984(Macdonald , 1985. That no geophytes have successfully invaded the reserve is possibly a further reflection of this type of selective pressure. The reserve has a high density of mole rats which feed mainly on geophytes. The large number of geophyte species in the indigenous flora presumably have adaptations that enable them to survive this predation pressure. However, geophytes from other mediterranean-type regions have not been subjected to such pressures (Milewski & Cowling 1985).
The role of ungulate herbivores in alien plant invasions in the reserve needs to be researched: on one hand, the introduction of these ungulates, most of which are alien to the reserve, is suspected to have led to the over-utilization of certain of the reserve's indigenous plants (Macdonald et al. in press). This might favour the establishment of alien plants, particularly where over-utilization leads to an opening-up of the plant canopy. On the other hand, the observations reported above indicate that ungulates might be limiting successful invasions. The interaction is complicated by two further considerations: the first of these is that the presence of these ungulates has been the stimulus for several intentional plant introductions to the reserve. The second is that alien plants might also have been unintentionally introduced in fodder imported to supplement the nutrition of these ungulates.
Although the collection of data on the alien flora of the reserve has been intermittent it appears that at least 8 species have been recorded from the reserve for the first time in the 1980s (Bromus molliformis, Cortaderia selloana, Sesbania punicea, Vicia benghalensis, Tropaeolum majus, Callistemon rigidus, Nicotiana g/auca, Orobanche ramosa). If these were all new additions to the reserve's alien flora this would give an invasion rate of at least one species per year. On the currently observed ratio of problem species to total alien species (7:73) this rate of invasion can be expected to give rise to about one new problem species per decade.
Two important management considerations arise from the above analyses. Firstly, no more tree species should be introduced to the reserve. Secondly, sites of human disturbance should be severely limited. Obviously, every effort should be made to prevent the inadvertant introduction of new alien species to the reserve, e.g. in fodder imports or during the movement of soil for roadbuilding and erosioncontrol purposes. A system of regular monitoring around sites of human disturbance should be initiated to enable the early detection of new invasions.