Invasive Alien Plants And Their Impact On Wetlands

Invasive alien plants multiply rapidly once they are established in an area, which increases clearing costs and compounds adverse effects on the environment. These species have established sustained self-propagating populations and spread considerable distances from the site of introduction.

- Farai Tererai

Invasive alien plants are introduced either intentionally or unintentionally. Plants that were introduced intentionally were brought into the country for horticulture, aquaculture, agriculture, and forestry. Plants that were introduced unintentionally entered the country as commodity contaminants, or as stowaways on trucks, airplanes, and ships.

How alien plants spread

Once these species arrive, some naturalize to the local conditions, including climate factors. They accomplish this through superior competitive capabilities, which include fast growth, high reproductive output and the ability to adapt to a wide range of physical environments. In many cases, these invasive alien plants establish dominance and form monocultures or homogeneous populations.

These species spread rapidly in rivers or streams and their margins, collectively known as riparian zones, as well as wetlands, because these systems are inherently highly dynamic and connected.

Riparian zones and wetlands, which usually cover only a small part of the landscape, experience much disturbance due to the natural processes of flooding, erosion, deposition, river damming, and land use next to rivers. Consequently, they are highly susceptible to invasion.

Rivers serve as conduits for substantial fluxes of materials and energy, thus dispersing alien plants. Wetlands are known for trapping material transported by rivers, which is why rivers and wetlands are the most heavily invaded ecosystems. This phenomenon causes substantial changes to ecosystem structure and function.

Common invaders of wetlands

Approximately 26 alien plant species are listed as invasive in the inland aquatic ecosystems of South Africa, which includes wetlands.

The Southern African Plant Invaders Atlas database indicates the most common invaders of rivers and their fringes. These plants include: