By Whitney Akinyi

A new study conducted by the Centre for Agriculture and Bioscience International (CABI), an international intergovernmental organization, has unveiled three highly effective methods to fight against the invasive Prosopis juliflora tree in Ethiopia, Kenya, and Tanzania.

Prosopis juliflora, introduced to Eastern Africa in the 1970s to address wood and fodder scarcity and combat land erosion, has rapidly spread, becoming one of the most menacing non-native tree species globally.

Its invasive nature has resulted in various detrimental consequences, including the loss of grazing land, restricted access to water, declining biodiversity, compromised human health, and increased conflicts among humans and wildlife.

The findings revealed that the treatments involving complete removal of above-ground biomass, namely manual removal and cut stump, yielded more productive and diverse vegetation compared to the basal bark treatment that killed the trees while they stood.

The restoration interventions, while showing varying rates of vegetation establishment and species composition, resulted in the establishment of grassland vegetation, including a substantial fraction of perennial grasses, suggesting the potential for reversing the impacts of Prosopis juliflora and providing support for livelihoods.

Dr. Rene Eschen, lead author of the study and Senior Scientist at CABI’s center in Switzerland, emphasized that the study demonstrates the possibility of restoring land previously invaded by Prosopis juliflora. The choice of control method depends on resource availability, including herbicides, and the intention for land use post-Prosopis management. Furthermore, the researchers highlight the cost and time investment, as well as the subsequent vegetation development, which varies among the different methods employed to eliminate Prosopis trees.

The three-year study encompassed three regions: Ethiopia’s Afar National Regional State, Kenya’s Baringo County, and Tanzania’s Moshi District.

In addition to the successful eradication methods, the researchers tested three incremental restoration interventions: divots, divots, and mulching, and divots and mulching with grass seed sowing. This demonstrates that cut stump and basal bark herbicide application, as well as manual uprooting, successfully eradicated the trees in nearly 85-100% of cases, the study noted.

Dr. John Richard Mbwambo from the Tanzanian Forestry Research Institute added that further studies are necessary to assess whether the initial investment in Prosopis treatment is offset by the economic benefits provided by grassland established after the removal of Prosopis. Nevertheless, the study indicates that increased availability of fodder can result in significant livelihood benefits.

“Most of the restoration practices did not have a significant impact on the species re-establishment and further studies are needed to determine whether the initial investment in Prosopis treatment is offset by economic benefits provided by grassland established following removal of Prosopis. Yet, these results indicate that significant livelihood benefits may be obtained as a result of the increased availability of fodder,” said John Richard.

CABI has been actively studying Prosopis and its impact on water usage and rural livelihoods in Ethiopia’s dry Afar Region since 2015, as part of the long-term Woody Weeds project.

The subsequent Swiss-Kenyan Woody Weeds + project, launched in 2019, aims to support Kenya’s National Prosopis Strategy by facilitating the sustainable management of Prosopis juliflora. The project will collaborate with relevant stakeholders in Baringo, Isiolo, and Tana River counties, targeting areas along the southern edge of Kenya’s northern rangelands.

This research aligns with a project funded by the Darwin Initiative, currently active in Tanzania, which complements the National Invasive Species Strategy and Action Plan (NISSAP). The project aims to protect Tanzania’s biodiversity, ecosystem services, and livelihood assets from invasive species, including the starting invasion of Prosopis juliflora in the Lake Natron Basin.

The study was supported by the Swiss Programme for Research on Global Issues for Development (r4d), funded by the Swiss National Science Foundation and the Swiss Agency for Development and Cooperation, through the project ‘Woody invasive alien species in East Africa: Assessing and mitigating their negative impact on ecosystem services and rural livelihood.’