The first paper from Theo Linders’s PhD work has been published in the Journal of Ecology.

The study assessed how Prosopis impacts a range of biodiversity and ecosystem functioning indicators in Afar, Ethiopia, and Baringo, Kenya. We found that Prosopis had a clear negative impact on both plant species richness and herbaceous biomass. Losses in plant species richness and biomass cascaded through the system, resulting in changes in invertebrate abundance and decreasing soil fertility and stability.

Our results highlight that not only plant species richness can affect ecosystem functioning, but changes to one ecosystem function, herbaceous biomass, can also significantly affect other ecosystem functions. For Prosopis management the results mean that just removing Prosopis is unlikely to be enough to restore healthy ecosystems, and that high plant species richness and herbaceous biomass are prerequisites for a healthy ecosystem.

Reference: Linders, T.E.W., Schaffner, U., Eschen, R., Abebe, A., Choge, S.K., Nigatu, L., Mbaabu, P.R., Shiferaw, H., Allan, E. (2019) Direct and indirect effects of invasive species: biodiversity loss is a major mechanism by which an invasive tree affects ecosystem functioning. Journal of Ecology. doi:10.1111/1365-2745.13268

A new video, made by Charles Kilawe of Sokoine University of Agriculture, features various stakeholders in northern Tanzania telling about the impacts of Prosopis on their livelihoods. Some stakeholders also talk about how involvement in the local implementation groups (LIGs) organised by the Woody Weeds project helps their community taking decisions about potential management of this species.

Last week, John Richard, Charles Kilawe and René Eschen interviewed people affected by Prosopis juliflora in the area south of Moshi town, Tanzania. This is part of the r4d Digital Storytellers project, which aims to document how r4d projects help to achieve the Sustainable Development Goals (SDG) of the 2030 Agenda for Sustainable Development.

Among other impacts, Prosopis severely reduces access to grazing land and the amount of available fodder and it increases the cost of farming. The species has started invading Tanzania relatively recently and various communities in the region are affected. The Woody Weeds project facilitates decision making by so-called Local Implementation Groups (LIG), consisting of diverse stakeholders, about management of Prosopis in their communities. The appropriate management options differ depending on the stage of the invasion. The interviewees spoke about the impact of the Prosopis invasion on their livelihoods and their involvement in the LIGs. They also explained the management methods for prevention, early eradication and control of Prosopis that are being tested.

A chairman tells about how Prosopis threatens grazing lands in his community and how three communities will jointly implement Early Detection Rapid Response measures to prevent the invasion.

Similar interviews were held in Baringo (Kenya). In Amani (Tanzania), we interviewed LIG members about the impacts of Lantana camara, Clidemia hirta and bracken, Pteridium aquilinum, on agriculture in their area and the sustainable land management practices that are tested as part of the LIG activities.

(reblogged from the CABI Invasives blog)

CABI scientists have revealed the massive ecological and economic impacts that the invasive alien tree Prosopis juliflora has had across the Afar Region of north eastern Ethiopia.

Dr Urs Schaffner, who is supervising lead author Mr Hailu Shiferaw for his PhD studies, contributed to the Science of The Total Environment published research which shows that the devastating Prosopis was a major reason for losses in annual ecosystem service values in Afar Region estimated at US $602 million in just 31 years.

Mr Shiferaw, in the paper entitled ‘Implications of land use/land cover dynamics and Prosopis invasion on ecosystem service values in Afar Region, Ethiopia’, highlighted that between 1986 and 2017 the weed spread at a rate of 31,127 ha/year while grassland and bush-shrub-woodland declined at a rate of 19,312 ha and 10,543 ha/year respectively.

Mr Shiferaw, from the Water and Land Resource Centre of Addis Ababa University, Dr Schaffner and colleagues from Botswana University of Agriculture and Natural Resources, the School of Agricultural Economics & Agribusiness, Haramaya University in Ethiopia, and the Centre for Development and Environment (CDE), University of Bern, in Switzerland, said local communities perceive that climate change, frequent droughts and invasive species are the main drivers of land use/land cover changes.

During the 19th and 20th centuries, various species and hybrids of Prosopis – native to South and Central America – were planted in areas outside of their native range including Australia, southern Asia and eastern Africa. The aim was to provide firewood, charcoal, fodder and timber to stabilize soil in degraded ecosystems and prevent desertification.

While the first introductions in Ethiopia were made during the 1970s and 1980s, problems soon arose in the early 1990s when the tree started invading croplands, grasslands, riverbanks and roadsides – causing significant environmental impacts and a source of conflict among pastoralist groups due to the effect on dwindling grazing land.

Mr Shiferaw said, “Our study provides evidence that land use and land cover changes in the Afar Region have led to a significant loss in ecosystem service values, with serious consequences for the livelihoods of the rural people.

“Negative net changes were found for grassland, bareland, bush-shrub-woodland, and natural forests as a result of the Prosopis spreading so rapidly.” About 50% of the lost grassland is now dominated by Prosopis. Hence, Prosopis causes serious negative effects on pastoralism, the traditional livelihood form in the region.

In a previous paper ‘Modelling the current fractional cover of an invasive alien plant and drivers of its invasion in a dryland ecosystem’, published in Scientific Reports, Mr Shiferaw and his team of international scientists suggested that the migration of livestock and wildlife could have contributed to the distribution of the woody weed but state this claim requires further investigation.

The scientists also believe that river courses, particularly during flooding events, are known to serve as modes of transportation of Prosopis pods and seeds to downstream areas – a process otherwise known as corridor dispersal.

In respect of the paper in Scientific Reports, Mr Shiferaw said, “In particular, our findings revealed that the invasion of riparian habitats along the Awash River will continue downstream, thereby, quickening the loss of drought-season grazing areas which may aggravate conflict among pastoralist communities.”

The researchers say that despite the potential benefits of Prosopis, by way of firewood and charcoal, Ethiopia has declared it a noxious weed and has recently published a Prosopis management strategy to try and manage it.

Full paper reference (open access)

Shiferaw, H., Bewket, W., Alamirew, T., Zeleke, G., Teketay,D., Bekele, B., Schaffner, U., and Eckert, S. 2019. Implications of land use/land cover dynamics and Prosopis invasion on ecosystem service values in Afar Region, Ethiopia. Accepted on 13 April 2019 Vol 675, Science of the Total Environment. DOI: 10.1016/j.scitotenv.2019.04.220

Ketema Bekele, one of the six PhD students in the first phase of the Woody Weeds project, has successfully defended his thesis earlier this year. The title of the PhD dissertation is “Impacts of Prosopis Spp. on Environment and Livelihoods in East Africa: Evidence from Ethiopia and Kenya” and the advisory committee consisted of Prof Jema Haji and Dr Belaineh Legesse of Haramaya University and Dr Urs Schaffner of CABI Switzerland.

The Woody Weeds team is of course excited about the achievement and congratulate Dr Bekele.

Two chapters of the thesis have recently been published in peer-reviewed journals:
Bekele, K., Haji, J., Legesse, B. and Schaffner, U. (2018) “Economic impacts of Prosopis spp. invasions on dryland ecosystem services in Ethiopia and Kenya: Evidence from choice experimental data” J. Arid Env. 158: 9-18
Bekele, K., Haji, J., Legesse, B., Shiferaw, H. and Schaffner, U. (2018) “Impacts of woody invasive alien plant species on rural livelihood: Generalized propensity score evidence from Prosopis spp. invasion in Afar Region in Ethiopia” Pastoralism: Research, Policy and Practice 8: 28