How South Africa’s second most invasive tree can be managed better

09 November 2016

mediumMany plants have been moved around the world for many reasons, whether for ornamental, forestry or agricultural purposes. A small proportion has become invasive, spreading beyond the areas in which they were initially planted. In some cases this has negatively affected humans and the environment.

One such tree genus, Prosopis, or mesquite, originally from the Americas, has been introduced to more than 100 countries. It was introduced into the arid parts of South Africa to aid farmers and local communities with fodder production, provide shade for livestock and produce firewood.

It has now invaded large parts of the country and has become the second-most widespread invasive tree after Australian acacias. It has had a negative impact on biodiversity, livestock production, land value, human health, infrastructure and water supply. These are all crucial factors for the economy and for local people’s livelihoods.


The negative effects of these invasions have led to the initiation of programmes to manage them across the world. In South Africa the Working for Water programme drives management on state and private land along with input from private landowners. Without active management these invasive plants would become more widespread and their impact on people and the environment would be more pronounced.


Management initiatives, such as Working for Water, aim to reduce the impact and spread of invasive plants. In South Africa the initiative also aims to create jobs and drive rural development.


The Conservation and Invasion Biology Department at Stellenbosch University recently conducted a study to assess the barriers that impede the effective management of widespread Prosopis invasion. More than 100 barriers that hinder current management operations were identified in the study. The results could be used to come up with solutions.


The key barriers identified were:

  • Using versus removing the tree and control options. Some parties wanted to continue using Prosopis for fodder and fuelwood and did not want them removed. Others pointed to the serious negative impact they have. Amongst those who want the Proposis removed, there was also controversy about labour-intensive management, related to Working for Waters Expanded Public Works Programme (EPWP) model, which is time consuming and makes progress slow. Mechanical and biological control approaches are obviously faster, but employ fewer people.
  • Proposis is hard to control because it grows very fast and spreads rapidly. It is also capable of regrowing from cut stumps if herbicide is not applied correctly.
  • Management operations are hampered by poor planning and prioritisation. Often no systematic control strategy is followed.
  • There is a lack of co-ordination and cooperation, linked to poor planning, inefficient management, and lack of collaboration between different government departments and farmers.

There were differences in perception of the importance of some barriers. Most farmers (80%) placed high importance on a lack of planning and poor management as important barriers. Few managers (20%) regarded these as important. This reflects different views about the context in which management projects operate.

Many of the barriers can be overcome, and ways to do this were identified in some instances. But not all were conducive to simple solutions. Key adaptive responses relate to the adoption of more effective clearing methods. These include:

  1. Mechanised options and biological control. These are more time and cost effective, but can still allow for job creation.
  2. Raising awareness and building partnerships to ensure that different actors work together to control the problem.
  3. Ensuring landowner follow-up control. This will ensure state investment is not wasted and long-term control is guaranteed. It is legally binding, but not enforced.
  4. Improved monitoring to get an understanding if control is working and of its benefits. This can also help to reduce inefficient management.
  5. Incorporating systematic strategic planning at various levels to ensure the limited funds available are spent wisely.

All of this will improve the effectiveness of control programmes with the funding available. YouTube video clip

By: Ross Shackleton, Post Doc student in Conservation and Invasion Biology, Stellenbosch University 

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