‘Early detection and rapid response’ to stop spread of woody weeds in Eastern Africa

A team of international invasive plant experts are recommending a coordinated management plan to halt the scourge of woody weeds threatening rangeland and biodiversity in Eastern Africa.

Lead authors of a new study in Ecosphere, Dr Sandra Eckert, Centre for Development and Environment, University of Bern, Switzerland, and CABI’s Dr Urs Schaffner, say that unless steps are taken to control Prosopis juliflora and Lantana camara it could spread to unreached areas of Kenya, Ethiopia and Tanzania.

P. juliflora and L. camara are both considered to be amongst the world’s 100 worst invasive species with the former being introduced in the 1970s and 1980s as part of dryland reforestation programmes and the latter in the 19th century as an ornamental plant.

However, the scientists, including those from the University of Nairobi, Sokoine University of Agriculture in Morogoro and the Water and Land Resource Centre in Addis Ababa, suggest that these noxious weeds – excaberated by climate change – will seriously impact upon grazing land and drive out native flora and fauna if left unmanaged.

Dr Eckert said, “The semi-arid to arid regions of Ethiopia and Kenya, essentially all areas up to 1600m, are either currently or at risk of being invaded by P. julifora. It has also started to invade the north of Tanzania and could even affect neighbouring regions such as Sudan and South Sudan.”

A previous study co-authored by Dr Eckert and Dr Schaffner showed that P. juliflora can spread very rapidly; in the Afar region in Ethiopia, this weed has invaded 1.2 million ha of rangeland, shrubland and crop fields within 35 years.*

Dr Eckert added, “Our data clearly show that the whole Afar and large parts of the Somali region are suitable for invasion by P. juliflora, so these lowland regions, once known for their grasslands and pastoralist communities, are seriously threatened.

“In respect of L. camara, the Ethiopian and Kenyan highlands as well as northern and central Tanzania have the highest risk of invasion. Our model suggests that Zambia could also be a target in the future.”

The researchers believe that a ‘spatially explicit management strategy that ensures concerted communication and management across national and subnational borders’ is needed to nip the woody weeds scourge in the bud.

Dr Schaffner said, “Our results reveal that ‘early detection and rapid response’, i.e. the identification of the first trees in new areas and a rapid removal of these trees, will be key for slowing down the fast spread of P. juliflora. Surveillance of areas still free of P. juliflora is warranted not only within the boundaries of the current climate, but also in areas which will become suitable in the context of climate change.

“In the case of P. juliflora, the planting of saplings and dispersal of seeds should be prohibited in areas bordering the current range of suitable habitats – for example south-western Tanzania and northern Zambia.

“In respect of L. camara our findings indicate that this species has already colonized a significant part of its ecological niche in Eastern Africa and that prevention measures may be less warranted than with P. julifora. Rather, management should be targeted at preventing L. camara from building up high local densities, as currently observed in areas bordering Lake Victoria.

“We recommend that management is in line with more detailed maps of the invasive species’ current distribution – ideally with information on local abundance or cover.”

Full paper reference

Eckert, S., Hamad, A., Kilawe, C., Linders, Theo E.W., Ng, Wai-Tim., Rima, P., Shiferaw, H., Witt, A., Schaffner, U. (2019) Niche change analysis as a tool to inform management of two invasive species in Eastern Africa. Ecosphere, DOI:XXXXXX

The paper is available as an Open Access document and can be viewed here XXXXXXXX

*Additional references: Shiferaw, H., Schaffner, U., Bewket, W., Alamirew, T., Zeleke, G., Teketay, D., Eckert, S. (2019) Modelling current fractional cover of an invasive alien plant and drivers of its invasion in a dryland ecosystem. Scientific Reports 9(1): 1576.

Mbaabu, P.R., Ng, WT., Schaffner, U., Gichaba, M., Olago, D., Choge, S., Oriaso, S. Eckert, S. (2019) Spatial evolution of Prosopis invasion and its effects on LULC and livelihoods in Baringo, Kenya. Remote Sensing 11(10): 1217.

Funding

Swiss Programme for Research on Global Issues for Development (r4d), funded by the Swiss National Science Foundation (SNSF) and the Swiss Agency for Development and Cooperation (SDC), for the project “Woody invasive alien species in East Africa: Assessing and mitigating their negative impact on ecosystem services and rural livelihood.”

Urs Schaffner was supported by CABI with core financial support from its member countries.

About the Centre for Development and Environment (CDE)

CDE is Switzerland’s centre of excellence for sustainable development. One of the University of Bern’s strategic research centres, it conducts research and teaching on behalf of a more sustainable world. CDE’s aim is to chart pathways to sustainable development and to initiate transformations in line with the UN’s 2030 Agenda for Sustainable Development. The centre combines sound research with inter- and transdisciplinary approaches to analysis and transformation. Its research agenda is created within long-standing partnerships spanning the global North and South.

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About CABI

CABI is an international not-for-profit organization that improves people’s lives by providing information and applying scientific expertise to solve problems in agriculture and the environment.

Through knowledge sharing and science, CABI helps address issues of global concern such as improving global food security and safeguarding the environment. We do this by helping farmers grow more and lose less of what they produce, combating threats to agriculture and the environment from pests and diseases, protecting biodiversity from invasive species, and improving access to agricultural and environmental scientific knowledge. Our 49 member countries guide and influence our core areas of work, which include development and research projects, scientific publishing and microbial services.

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