A revised list of alien plants for the Kruger National Park

2003. A revised list of alien plants for the Kruger Park. 21-44. ISSN Alien plants recorded in the Kruger National Park are listed, providing an update of species that have been recorded since the last published list in 1988. The serious conse-quences that invasive alien plants pose are widely recognised internationally and are regarded as the greatest threat to the Kruger National Park. It is extremely important to maintain an updated list of species to use as a reference and from which to monitor changes in the influx of invasive species. The list contains the invasive status of the plants, current impact, habitat types, biological control status and status according to the Conservation of Agricultural Resources Act (CARA), Act 43 of 1983, as amended in March 2001. The list comprises 370 species, of which 121 are invaders and two are transformer weeds, which may cause considerable damage and alterations to the indigenous biodiversity. A total of 91 species listed herein are also listed in the CARA regulations or are proposed additions to the CARA regulations.


Introduction
The species list in this paper contains reference to lists previously published by a number of authors of alien plant species recorded in the Kruger National Park (KNP). The first published list was by Obermeijer (1937), who listed six alien plant species ("troublesome weeds": Chenopodium ambrosioides L., Tagetes minuta L., Argemone mexicana L., Gomphrena celosiodes Mart., Boerhavia diffusa L., and Cocculus hirsutus (L.) Diels. (Foxcroft & Richardson 2003), thereafter Codd (1951) indicated 32 species, Van der Schijff (1957& 1969 indicated 43 and 76 species, respectively, and Macdonald & Gertenbach (1988) listed 150 alien plant species. Between 1988 and 1997, the species list increased to 216 species (KNP alien plant section records). In February 1999, Nichols and Foxcroft undertook a survey in the Skukuza personnel village listing approxi-mately 243 species. The number of alien plant species in the KNP then totalled approximately 360 species, prompting a revision of the KNP alien plant list to provide a more accurate reflection of the records. Figure 1 indicates the increase in alien plant species in the KNP. The long-term average increase in alien plant species, since the first record of alien plants was made in 1937, is 5.6 alien species per year. Thirteen species have been removed from the list presented by Macdonald & Gertenbach (1988), as information now indicates that these species are probably indigenous (Appendix 1).
The list further provides information on the status of the weed and its current impact in the KNP, as well as its biological control and legal status for South Africa. The date provided is that of the first record for the species or when the species was first listed in publications. 'M&G' is added to the date column to indicate plants listed in the last published list (Macdonald & Gertenbach 1988). All plants not indigenous to the KNP lowveld have been listed in a manner similar to Macdonald & Gertenbach (1988).
the extent of that ecosystem (denoted by T).
Where the species is considered as a potential transformer, PT is added.
Impact on the KNP is noted as the current known impact, and rated as high (H), moderate (M) or low (L). This information is an estimate based on records of the species in the KNP and the authors' personal experience.
The habitat types where the plants are currently observed in the KNP are: disturbed areas and roadsides denoted by the symbol (DR), villages and rest camps (V), aquatic habitats (A), riparian/riverine (R) and terrestrial/dryland habitats (TD).
Status of biological control is indicated at two levels; that taken from the national biocontrol list (Olckers & Hill 1999); and, that for the KNP ( -DW1: Declared weed (category 1) are prohibited plants which must be controlled, or eradicated where possible (except in biocontrol reserves, which are areas designated for the breeding of biocontrol agents); -DI2: Declared Invader (category 2) are mainly commercial plantation species but also plants for woodlots, animal fodder, soil stabilisation, etc., allowed only in demarcated areas, by permit holders, under controlled conditions and in biocontrol reserves; -DI3: Declared Invader (category 3) are mainly ornamental species that may no longer be planted (except with special written permission), nor may there be trade in propagative material. Existing plants may remain but must be prevented from spreading.
All three categories of plants are prohibited within 30 m of the 1:50 year floodline of watercourses or wetlands, unless exemption is obtained. The full regulations and species list are given in Henderson (2001). is indicated by Fig. 2. The basic under-riding principle of the South African National Parks (SANParks), "to preserve biodiversity in all its natural facets and fluxes" (Braack 1997) is directly violated by the introduction, whether intentional or accidental, of alien organisms, and according to definition, indicates the requirement to remove or control all alien species. In practice, the control of prioritised transformer and invader species, to acceptable limits of abundance, is the most likely scenario. At this minimal level of abundance, the impact on biodiversity (as described by Noss 1990) is hoped to be minimal. Macdonald & Gertenbach (1988) stated that the increase in number of alien plant species recorded for the KNP was probably due to increased collecting and awareness between 1937 and 1983. Further increase may also be ascribed to increased tourism (Macdonald 1988), which has unintentionally brought in seeds from other infested parts of the country as well as increased infestation of the lowveld. Infestations and new species may also have arisen due to the considerable increase in size of towns such as Nelspruit and others along the escarpment, over the past 50 years.

Discussion
Although Macdonald & Gertenbach (1988) state that 10 species had been eradicated, at least four of these (Senna didymobotrya,  Table 1 Revised alien plant list for the Kruger National Park  Macdonald & Gertenbach (1988) also reported that Solanum mauritianum was first reported along the Crocodile River and was either eradicated or later failed to be reported as present along the river by officials from Skukuza. This indicates that, for a reserve the size of the KNP, the likelihood of a species being eradicated is remote once listed, and it may appear in another area at a later stage. Furthermore, the large infestations of most of these weeds on the boundaries of the KNP make it unlikely that only a few plants will enter the KNP and re-invasion by the plants is inevitable.
Evidence to prove the lag phase and our limited knowledge of the ability of alien plants to become invasive is borne by the listing of 43 species by Macdonald & Gertenbach (1988) as non-invasive. Of these species, 17 are now well-known invasive species, while seven have since become invasive in the park. In a national park, which aims at the protection of indigenous biodiversity, policy should rather err on the side of caution. The removal of all alien species accompanied by the replacement thereof with indigenous species should be promoted. Although a species may not, at a single point in time, exhibit a tendency to invade, the lack of knowledge of the species and the long phase that is often found to prelude an explosion in the distribution of invasive species, places most species in an unknown category. This may result in serious, often immense, insidious and irreversible problems at a later stage (McNeely 2000), as species enter a rapid growth phase.
The habitat invaded indicates that the vast majority of the species occur, or occurred, in the staff villages or rest camps (320 species) and is of concern (Fig. 3 Examination of the plant list indicates the total number of plant families represented is 98, of which eight families collectively contain 125 species (or 35 % of the total) (Fig. 4). The other 90 families contribute to the remaining 245 species.
Impact ranking assigned to the species indicates that 87 % of the species are rated as having a low impact, 7 % medium and 4 % as having a high impact (Fig. 5). Although the perception may be created that invasive species therefore represent a minimal impact to the KNP, the combined effects of only a few invasive species can have major consequences and result in dense stands that cover vast areas.

Conclusion
Invasive alien plants have been recognised as one of the greatest threats to the biodiversity of the KNP (Braack 1997). In order to address this, proactive work on the prevention of species reaching and infesting the KNP is necessary. Early detection is the single most important step in combating the plants. While still in the early stages of invasion, the plants may be removed before they are able to set seed and become established. Updated species lists provide a firm base from which to work and are necessary to determine new invasions in an area as well as the rate of invasion. It is however only a starting point as spatial data is needed to determine the areas invaded, the extent to which they are invaded and the densities of invasions, in order to make meaningful interpretations and recommendations.