Protecting Kruger’s Wilderness

What Are Alien Invasive Species?

Alien (or exotic) species are organisms that humans have moved, intentionally or accidentally, outside their natural range. Not all alien species become invasive — many remain contained in gardens or agricultural areas. But when an alien species begins to spread on its own and causes ecological, economic, or social harm, it becomes invasive.

In Kruger National Park, invasive plants are the most visible culprits. More than 300 alien plant species have been recorded, and around 35 are considered invasive or problematic. Common offenders include Lantana camara, Chromolaena odorata, Opuntia (prickly pear), Eucalyptus trees, and Melia azedarach (syringa).

These species were mostly introduced as ornamentals, shade trees, or for erosion control decades ago — long before their destructive potential was known. Once established, they spread through seeds, wind, animals, and rivers, infiltrating wild areas and replacing native vegetation.

Why Invasive Species Are a Problem in Kruger

Invasive species pose multiple, interconnected threats to Kruger’s ecosystems:

1. Loss of Native Biodiversity

Dense stands of alien plants outcompete indigenous flora, shading out smaller plants and changing soil chemistry. As native plants disappear, so do the insects, birds, and mammals that depend on them, leading to a cascading loss of biodiversity.

2. Reduced Water Availability

Some invasive trees — especially along rivers — consume vast amounts of water. Studies have shown that species like Eucalyptus and Poplar can drastically lower groundwater levels and reduce streamflow. In a semi-arid park like Kruger, where every drop matters, this is a serious threat to both wildlife and downstream communities.

3. Altered Fire Patterns

Many invasive plants change the fuel load and fire intensity. Some make fires burn hotter and faster, while others suppress fire entirely — disrupting the natural fire regimes that shape savanna ecosystems.

4. Economic and Management Costs

The financial cost of controlling invasive species is enormous. Clearing, chemical treatment, monitoring, and follow-up work cost millions of rand annually. Without continuous funding and manpower, cleared areas can quickly become re-infested.

5. Aquatic Impacts

Aquatic invasives like water hyacinth (Eichhornia crassipes) and Salvinia molesta choke waterways, block sunlight, and deplete oxygen levels, leading to fish deaths and loss of aquatic biodiversity. These floating mats also hinder tourism and recreation along rivers and dams.

A Long Battle: Kruger’s History of Control Efforts

Kruger’s fight against invasive species began decades ago. By the early 1980s, park managers had identified alien plants as a significant threat to ecological integrity. Early control focused mainly on visible infestations near camps and roads.

In the 1990s, the Working for Water programme — a national initiative by the South African government — revolutionized invasive plant management in protected areas, including Kruger. It provided funding, training, and employment for local communities to remove water-thirsty alien plants along river systems and catchments.

Partnerships between SANParks scientists, universities, and NGOs strengthened Kruger’s ability to prioritize species and track the effectiveness of control operations. Over time, management evolved from simply “removing plants” to a strategic, data-driven approach based on ecological impact and spread potential.

Methods Used to Control Invasives in Kruger

Kruger employs a mix of traditional and modern strategies to combat invasive species. The park’s approach is integrated, using multiple methods depending on the species, habitat, and scale of infestation.

1. Prevention and Early Detection

Prevention is the most cost-effective weapon. Park staff and residents are educated about which species are invasive and discouraged from planting them in gardens. Vehicles and equipment are cleaned to avoid spreading seeds, and high-risk areas like riverbanks and roadsides are regularly inspected for new incursions.

2. Mechanical Control

Mechanical removal — pulling, cutting, or bulldozing — is effective for small infestations or where chemical use could harm non-target species. Crews manually uproot young plants, cut larger ones, and dispose of them safely to prevent re-sprouting.

However, mechanical methods are labour-intensive and often need to be combined with herbicide treatment to stop regrowth.

3. Chemical Control

Herbicides are applied in a targeted way, such as stem injections, basal bark applications, or foliar sprays. These treatments are performed by trained teams who ensure minimal environmental damage, especially near water sources.

4. Biological Control

Biological control — introducing natural enemies from a species’ home range — offers long-term, cost-effective suppression. Kruger has successfully used biological agents such as weevils that feed on water hyacinth and cactus moths that target Opuntia species.

These methods are safe when carefully tested, and they help reduce the need for continuous chemical spraying in remote or sensitive areas.

5. Monitoring and Research

Every cleared site in Kruger requires regular follow-ups. Without consistent monitoring, a cleared area can revert to dense invasion within a few seasons. Researchers also study the effectiveness of different methods, ensuring that management remains adaptive and evidence-based.