Woody invasive alien species in Eastern Africa

village thickly overgrown with Prosopis juliflora
A village thickly overgrown with Prosopis juliflora.

Many exotic trees and shrubs have been introduced to Africa. Some of them, for example Prosopis spp. or Lantana camara, have become invasive and are threatening important ecosystem services. In South Africa alone, invasive alien plant species have been estimated to cause costs related to the loss of ecosystem services of USD 1 billion annually.

Woody invasive alien species affect ecosystems and local livelihoods

In Eastern Africa, where peoples’ livelihoods still strongly depend on natural resources like grassland, cropland, forests, and water, the impacts of invasive species are severe. At the same time, there is a lack of reliable information on where, how, and to what extent natural resources and people are affected. Accordingly, there is also a lack of coordinated and effective sustainable management of woody invasive alien species.

The project areas of "Woody Weeds": Afar (Ethiopia), Baringo (Kenya), Moshi and Amani (Tanzania). Map: Sandra Eckert; Landsat background imagery courtesy of U.S. Geological Survey

Understanding and mitigating impacts

CDE has been working to address this challenge as a key partner in two projects: The “Woody Weeds” research project (2015–2021) and the “Woody Weeds +” implementation project, which builds on the research results of the initial project.

The original inter- and transdisciplinary research project “Woody invasive alien species in Eastern Africa” (Woody Weeds) sought to mitigate the negative effects of woody invasive alien species on biodiversity, ecosystem services, and human well-being in Eastern Africa. To achieve this goal, the project focused on:

  1. Understanding how different levels of invasion impact natural resources and, consequently, on peoples’ livelihoods;
  2. Assessing the past, current, and potential future spread of selected woody invasive alien species in three case study areas and at national level, considering different climate scenarios;
  3. Based on these findings, developing and testing technologies for invasive species management – prevention, early detection and rapid response, as well as biological, chemical, and physical control – jointly with local implementation groups;
  4. Finding entry points into national policy processes with a view to fostering awareness and the uptake of sustainable land management practices.

CDE had a leading role in activities under 2–4.

Main research results

Research in Afar Region, Ethiopia, have shown the following:

  • In the 35 years since its introduction, Prosopis has invaded 1.17 million hectares of land. About 30% of which was formerly grassland.
  • The most severe Prosopis invasion occurred within a strip along roadsides and rivers. The banks of the Awash River, Afar’s main source of water, have been invaded to the point where local pastoralists and their livestock are no longer able to access the water.
  • Measurements in Afar showed that one tree absorbs an average of around 6.8 litres of water daily. This adds up to 3.1 to 3.3 billion cubic metres of water annually used by Prosopis throughout the invaded areas in Afar Region.
  • Reduced access to water and the degradation of grasslands has led to conflicts among local communities.

In Baringo County, Kenya, similar assessments yielded the following findings:

  • Prosopis coverage increased from 882 hectares in 1988 to 18,792 hectares in 2016. At the same time, grasslands decreased by 6,252 hectares, cropland by 2,281 hectares, and native tree vegetation by 3,602 hectares. All three land uses are important for rural people’s livelihoods and for biodiversity.
  • Healthy and restored grasslands store significantly more soil organic carbon than land covered with Prosopis.

The project successfully identified entry points into national policy processes through which it will promote the uptake of sustainable land management practices. Environmental ministries in three countries took action based on the project results:

  • In Kenya, project partners were requested to identify practical solutions for Prosopis management.
  • In Tanzania, three project scientists were appointed to a task force in charge of preparing a national strategy for the management of invasive alien species.
  • In Ethiopia, the Ministry is represented in the local implementation group of the Woody Weeds project.

Supporting the implementation of the National Prosopis Strategy in Kenya

In 2020, the Kenyan Government drafted a National Prosopis Strategy (NPS) with support from the Woody Weeds team. Afterwards, the project team was able to secure funds from the Swiss Agency for Development and Cooperation (SDC) to launch the new “Woody Weeds +” project, which aims to support the government in implementing the NPS, together with relevant stakeholders, in a target area stretching from West to East along the southern edge of Kenya’s northern rangelands. This belt is a crucial site of some of the most dynamic and threatening invasive plant processes.

The Woody Weeds + project has four main objectives:

    1. To support institutions at the national, sub-national, and local levels in concretizing and operationalizing the NPS by developing spatially explicit Prosopis management strategies and integrating them in land use, land restoration, and integrated development plans.
    2. To raise awareness among stakeholders about the long-term impacts of Prosopis invasion and accelerate the dissemination of adequate knowledge for its efficient, effective, and context-specific management.
    3. To create momentum for a broad implementation of Prosopis management by pioneering strategies in test areas and bringing land users on board.
    4. To find innovative financing mechanisms through funds and impact investment and secure the long-term sustainability of Prosopis management.
The healthy grassland protected by a fence in Baringo County, Kenya, contrasts starkly with the degraded land outside the fence, infested with Prosopis juliflora. Photo: Purity Rima

Achieving tangible behaviour change in land use and governance

CDE contributes in the use of artificial intelligence and machine learning to monitor the actual spread and risks of future contamination using satellite imagery. We are also leading the work package aimed at raising awareness about Prosopis, its sustainable management, and land restoration. It is striving to achieve tangible behaviour change in land use and governance

  • through face-to-face exchange with stakeholder groups;
  • through events and exchange visits;
  • by engaging with the media and equipping extension services with information and tools;
  • by providing knowledge on sustainable practices through a dedicated mobile app.

Finally, CDE is contributing to a business concept for impact investment to support long-term financing of sustainable Prosopis management and land restoration.

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