Invasive of the month: Prosopis

CABI and a number of collaborators have launched a project in Kenya that seeks to improve understanding of the country’s invasion by mesquite (Prosopis spp.) in order to enhance its management.

Native to arid and semi-arid regions of western Asia, Africa and the Americas, mesquite species have been widely introduced to other regions of the world due to their ability to survive in inhospitable locations and provide a source of fuel, timber, fodder and edible seedpods.

In Kenya, mesquite species were introduced – without any comprehensive risk assessment – to stop desertification and to provide fodder, charcoal and fuelwood in the dry zones of the country. The major introduction efforts in the 1980s were supported by local communities. However, mesquite species soon began spreading from their initial places of introduction and are now advancing rapidly, eliminating other species and threatening ecosystems, livestock and the livelihoods of thousands of people. For example, about 30 000 people are affected in Marigat Division in the Baringo District of the Rift Valley, where mesquite has been blamed for encroaching onto grazing land, blocking roads and watering points, drying up rivers and changing their courses, and causing the loss of teeth – and even death – in goats. This has led to a high-profile debate in the country, resulting in the Minister of Environment declaring mesquite a national disaster.

About half a dozen different mesquite species are reported to have been introduced to Kenya, but details on the materials brought in – including their sources – have been poorly documented. The project will therefore attempt to unravel the links between mesquite species composition and invasiveness. This will help to ensure that taxonomic considerations are given due prominence in any mesquite management efforts, such as the introduction of biological control agents.

The spatial distribution of mesquite will be mapped, allowing the identification of areas that are susceptible to invasion but not yet infested. Management measures such as prevention of and early warning and rapid response to new infestations can then be implemented in these areas.

Surveys of arthropods and microorganisms associated with mesquite in Kenya will also be undertaken, to quantify how mesquite invasion impacts upon key biodiversity components.

This work will also help in the identification of empty niches that could be filled by introduced biological control agents. The project is a collaborative initiative between CABI, the University of Fribourg, Swiss Federal Institute of Technology (ETH) and the World Agroforestry Centre (ICRAF), with funding support from the Swiss Agency for Development and Cooperation (SDC) through the Swiss Centre for International Agriculture (ZIL). It is hoped that the knowledge generated from this project can help to reduce the rate of spread of this controversial tree in Kenya as well as other affected countries.

Reference: Okello Ogutu W.  Unraveling the mysteries of mesquite in Kenya GISP Newsletter 7