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

The mesquite tree was introduced into South Africa to aid farmers and local communities. It is now invasive in most parts of the country. Shutterstock

Many plants have been moved around the world for many reasons – for example for ornamental purposes, forestry and agriculture. A small proportion have 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.

Reducing the impact

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.

We recently conducted a study to assess the barriers that impede the effective management of widespread Prosopis invasion. More than 100 barriers were identified in the study, which tried to identify the problems that hinder current management operations. The results could be used to come up with solutions about how to overcome these problems.

Prosopis invasions in South Africa: a blessing or curse?

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. There was also controversy about labour-intensive management, which is time consuming and makes progress slow. Mechanical and biological control approaches are obviously faster but employ fewer people.

  • The ecology of the species. It 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.

  • Poor planning and prioritisation. Often no systematic control strategy is followed.

  • Coordination and cooperation, which is linked to poor planning, inefficient management, corruption and lack of collaboration between different government departments and farmers.

There were differences in how the importance of some barriers were perceived. 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.

Adaptation responses

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 adaption responses include 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 also 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 and in a way that has the most benefit.

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