Invasive Species in the Kruger
Invasive Alien Species (IAS) have probably been present in the Kruger National Park (KNP) since its proclamation in 1898. Currently, approximately 360 alien plant species are recorded in the KNP.
These range from aggressively invading “transformer” weeds to less invasive “casual” alien plants.
However, as the main aim of a national park is to “conserve the indigenous biodiversity”, and as invasives are well known to be a threat to biodiversity, it is undesirable to have or allow any alien species in a national park.
The riparian zones are generally found to be the most heavily infested, with a wide array of species being recorded. Many IAS were introduced into the KNP accidentally, when plants were brought in to ‘beautify’ gardens and restcamps and later spread to the surrounding areas.
Well known examples are the prickly pear, Opuntia stricta (now infesting 35,000 hectares in the Skukuza area), Lantana camara that was planted in camps and villages, and now occurs widely along the rivers, and even aquatic weeds such as water lettuce (Pistia stratiotes), which is now found on many dams and rivers.
Many other species have spread into the KNP via rivers and possibly other means.
A number of species are currently being targeted in the Kruger, and are likely to be considered candidates for control in the Greater Limpopo Transfrontier Park of which the Kruger forms a part.
The following represent a partial list of Kruger's current invasive species problems:
Various Opuntia (jointed cactus) species (generally Opuntia ficus-indica) are known to occur along the Mozambique border and it is predicted that they are widely spread. A potential problem however may be that the species is utilized for its fruit;
Other Opuntia’s may also be found in the area, such as Opuntia stricta and O. rosea. These species have little or no commercial value and can rapidly invade dryland/terrestrial areas and form dense impenetrable thickets. Biological control is used as far as possible in these infestations in SA;
Eichhornia crassipes is currently found on the Letaba River at Engelhard dam and downstream. Biological control agents are used in the control of this weed on Engelhard dam as well as many other dams and lakes in Africa. The plants on Massingir dam should already have biocontrol agents on them as the plants carrying the insects in KNP would have spilled over into Massingir dam. Six different species of biological agents were released onto the plants;
Azolla filiculoides (red water fern) is also a well-known aquatic invader that became widespread throughout the KNP in a matter of 12 months. It could infest or already have infested Massingir dam and the Olifants river. The biocontrol agents are however extremely effective and travel great distances to find the plants. Pistia stratiotes (water lettuce) was found in the Levhvhu/Limpopo flood plain and may infest waterways further downstream. Once again, this is a species that can be controlled by biological control.
The two riparian zones of the Limpopo River and Olifants River are infested to varying degrees with a wide range of species.
General clearing activities are taking place in the KNP and upstream through the “Working for Water” programme.
The most problematic species recorded in these areas include Lantana camara, Chromolaena odorata, Caesalpinia decapetala, Senna spp., Mimosa pigra, Ricinus communis (although some areas don’t consider it an invasive alien plant), Nicotiana glauca, a wide array of annual species (e.g. Argemone, Datura and Xanthium), Cardiospermum halicacabum and also C. grandiflorum, Melia azedarach, Sesbania punicea, Solanum mauritianum and S. seaforthianum.
Monitoring of invasive species
The KNP Alien Biota Section is currently designing a monitoring programme for the monitoring of IAS in riparian areas. Opuntia stricta is currently recorded during chemical control and biocontrol operations by means of a GPS. Aquatic weeds are currently the most frequently monitored species, using fixed-point photos and the monitoring of biocontrol damage. Plant samples are collected and reared at the sections’ storerooms for the breeding of biocontrol agents. Host-specific insects are reared on these plants and then taken back to the infestation and distributed throughout the infestation. Records are taken of plant damage and number of insects on the plants in order to determine the numbers of biocontrol agents and the level of damage they are causing. Data from clearing operations and GIS data on distribution is available for IAS in the KNP. This is periodically written into internal scientific reports or publications.