Prosopis has started invading in Tanzania and this INSIGHTS brief, the first in a series produced by the Woody Weeds project, provides background, implications for policy and management options.

Key messages form this brief:

• The invasion of Prosopis trees in Tanzania is still at an early stage. Therefore, a national Prosopis strategy and methods to prevent further expansion of Prosopis and to sustainably manage it in invaded areas should be developed.
• National and sub-national authorities should coordinate Prosopis management and make resources available for its implementation. Awareness about the negative impacts of this species should be raised among extension services and other stakeholders.
• Established stands of Prosopis should be mapped and managed. Surrounding areas as well as areas bordering neighbouring countries with Prosopis invasion should be regularly surveyed and new infestations mapped and eradicated.
• Building on the management know-how from other countries (e.g. Australia and South Africa), physical, chemical and biological control options should be developed for Tanzania to manage Prosopis infestations where eradication is not feasible.
• Planting and intentional spread of seeds and seedlings should be prohibited. Animal consumption of Prosopis pods and seeds should be discouraged and livestock kept in a Prosopis-free zone for at least 48 hours prior to being moved to unaffected areas. Especially, the spread of Prosopis into sensitive ecosystems, such as national parks and other protected areas should be prevented.

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One of the PhD students in Woody Weeds Project, Mr Hailu Shiferaw, measures the amount of water consumed by Prosopis trees in the Afar Region of Ethiopia. He assesses the amount of water being used by Prosopis using eco-physiological and micrometeorological instrumentation.

The main technique used to understand water consumption at the tree level is measuring the flow of water through the stem of replicate Prosopis trees in a field study. The transpiration rate is measured using the stem sap flow method, in which sap flow through individual Prosopis trees is measured in trees of different diameter classes.

Sap flow measurements to calculate transpiration from individual Prosopis trees: sap flow measurement setup (left) and setup for data storage (right).

The second part of the field study is aimed at calculating evapotranspiration (ET) of a Prosopis-dominated plant community, so that triangulation with transpiration from individual Prosopis trees will be possible. Evapotranspiration is assessed using Eddy Covariance measures taken above the vegetation canopy, which reveal the amount of water transpired by the entire vegetation. The data is collected from a homogenous Prosopis-dominated vegetation block where the instrument is installed.

Eddy Covariance measurement to calculate evapotranspiration from Prosopis-dominated vegetation. Measurement instruments (left) and monitoring and downloading equipment (right) are mounted on an elevated position.

A preliminary analysis of the data shows that a single Prosopis tree consumes several liters of water per day during high photosynthetic active periods, suggesting an important impact of Prosopis on water availability at the study area. Hailu will continue his measurements and analyses to arrive at more definitive estimations of water consumption by individual Prosopis trees, but also by Prosopis at community level.

In our latest scientific publication we analyze the potential of novel high resolution satellite images to indentify, map and possibly monitor the invasive species Prosopis spp.



We found that it is possible to separate the highly invasive Prosopis spp. from co-existing indigenous Vachellia tortillis which both have similar spectral signatures. We evaluated the potentials of two recently launched satellite platforms that have high spatial resolutions, Pléiades and Sentinel-2A. Particularly, ESA’s Sentinel-2 constellation of two identical satellites in orbit by spring 2017 will be of high interest for the Woody Weeds project for the continuous and detailed montoring of invasive species encroachments.

Our comparative study can be found here

Wai-Tim Ng, Purity Rima, Kathrin Einzmann, Markus Immitzer, Clement Atzberger and Sandra Eckert. Assessing the Potential of Sentinel-2 and Pléiades Data for the Detection of Prosopis and Vachellia spp. in Kenya. Remote Sensing 2017, 9(1), 74; doi:10.3390/rs9010074

The management of woody alien invasive plants is a complex undertaking, and to achieve the goals of management effectively requires a strategic approach. Two African countries have recently published national strategies for managing alien invasive Prosopis trees.

In Ethiopia, the Ministry of Livestock and Fisheries published its “National strategy on Prosopis juliflora management” in January 2017. This official document presents a strategy aimed at i) preventing the expansion of Prosopis to uninvaded areas, ii) reclaiming and restoring invaded areas after Prosopis clearance and iii) sustainably managing Prosopis for productive use and increasing biodiversity through the regulation and coordination of Prosopis management initiatives. In February 2017, researchers from Stellenbosch University’s Centre for Invasion Biology published a proposal for a national strategy for the management of Prosopis in South Africa. This strategy considered all available control methods (including biological control, control through utilisation, and different combinations of chemical and mechanical control), and these were compared in terms of costs, effectiveness, and potential to create employment. The strategy concluded that biological control and more mechanised approaches were important, but that the effectiveness of control through utilisation requires urgent research to establish its potential usefulness before it is widely implemented. Both of these strategies provide essential frameworks within which the outputs of the Woody Weeds project can be placed. It is our intention to develop proposals for similar strategies for Kenya and Tanzania.

Ethiopia’s National Strategy on Prosopis juliflora Management

Ross T. Shackleton, David C. Le Maitre, Brian W. van Wilgen and David M. Richardson. Towards a national strategy to optimise the management of a widespread invasive tree (Prosopis species; mesquite) in South Africa. Ecosystem Services, 2017

A Woody Weeds meeting was held in Ethiopia from 7-11 June 2016 at Adama Town in the Rift Valley. The event included a progress review of PhD and MSc student work in the project and a field visit to the Awash Valley in the Afar Region, where the Prosopis invasion is the severest in the country, to assess the level of the Prosopis invasion and look at research sites. Prior to the project meeting, the six PhD students met for a two-day training workshop.

A highlight was the one-day stakeholder meeting that was attended by farmers and pastoralists from areas affected by Prosopis and Lantana, experts from Woreda Development Bureaus and the Ethiopian Institute of Agricultural Research and representatives from Awash National Park, the Federal Ministry of Livestock & Fisheries and non-governmental organisations working in Middle Awash.

The meeting was opened by Dr Daniel Temesgen, who is leading the team commissioned to design a strategy to manage the invasion of Prosopis in Ethiopia and his speech focused on describing the extent of the problem, exploring the challenges and the work government, in particular that of the Afar Regional State, and the intention of the government during the second Growth Transformation Plan Period.

In groups, the participants drew maps of the areas where Lantana and Prosopis invasion are found. After identifying the areas the current management practice, land use type, specific locations where management is practiced, approximate area covered and the main types of land degradation addressed were also indicated on the maps. Particular attention was paid to Sustainable Land Management practices that are currently employed.

Prosopis has spread from its original sources across the Middle Awash River Valleys and is now covering over 1.2 million hectares with 20 out of 32 woredas invaded. It continues to spread at a rate of at between 20-50 thousand hectares per year in Afar region alone. Participants indicated that Lantana is mainly an issue in eastern and western parts of the country. They said that the invasion is not as bad as Prosopis and the management not as difficult. However, Lantana takes grazing land and when there is no grass cattle and goats feed on it. When they eat too much it kills the animal, and spoils the taste of the milk. Participants indicated that the only use is for fire wood.

The participants indicated during group discussions that cattle herding and farming have become very difficult because of Prosopis, and there has not been any effective intervention by the government and NGOs. Participants from affected communities indicated that Prosopis is taking the best grazing land and that it is aggravating the already prevailing food insecurity as a result of climate variability and drought as it takes over good farmlands. Moreover, it hampers livestock mobility and visibility which allow Hyena and lion to come closer and pry on cattle. The manpower requirement for clearing the land makes cultivation more expensive: it requires up to 8000 Birr/ha to clear the land, which is expensive. There was also an argument that Prosopis thorns are not poisonous in themselves, but they can cut and poke holes in the skin of humans and animals, and the small wounds provide an entry point for pathogenic organisms. There was however a disagreement among the communities on his issue.

The meeting was closed with a pledge of the participants to provide the required support for the research undertakings of the Woody Weeds project and the organizers thanked those present for their participation and contributions during the meeting, despite the fasting period.

PhD students participating in the first phase of the Woody Weeds project presented their project outlines and some initial results during the recent project meeting in Adama, Ethiopia. The six students play an important role in the woody weeds project and we were excited to learn about their progress. In addition, four MSc students are carrying out research on the socio-economic and ecological aspects of the woody weeds project. The students have established active collaborations among themselves and they work together to collect field data. It is expected that this  interdisciplinary collaboration will contribute to achieving project outcomes and also to the professional development of the students. Below, we introduce the PhD students and give a brief summary of their research topics, objectives and methodologies.

MSc and PhD students of the Woody Weeds project in Adama, Ethiopia. Front row: Ms Maria Loreto Castillo, Ms Purity Rima Mbaabu and Ms Amina A Hamad. Back row: Mr Anteneh Abebe, Mr Hailu Shiferaw Desta, Mr Ousmane Seid, Mr Theo Linders and Mr Ketema Bekele. Photo credit: Urs Schaffner.

PhD students and research topics:

Maria Loreto Castillo (CIB, South Africa) – This research focuses on understanding the ecological-evolutionary dynamics that underlie the extraordinary invasive success of Prosopis species globally, with a focus on Kenya and Ethiopia. From a global perspective, Maria aims to use population genetic techniques and Prosopis individuals from invasive populations around the world to assess the incidence and extent of hybridization. On the local level, she aims to integrate genomic simulation modelling, experimentation and historic information about the introduction of the individuals to a) evaluate whether some species and/or their hybrid offspring are more likely to undergo range expansions, b) link dispersal ability and survival capacity to new habitat characteristics such as soil conditions or presence of pastoralist routes, c) identify potential routes of spread from the first planted individuals. A final important objective is to evaluate how this new knowledge on invasion processes can be applied to develop effective management options such as biological control.

 

Ketema Bekele (Haramaya University, Ethiopia) – The general objective of this PhD research is to measure the impact of woody weeds on rural livelihood and ecosystem services in East Africa, specifically Prosopis in Ethiopia and Kenya, and Lantana in Ethiopia and Tanzania. This research will (i) evaluate impact heterogeneity of these woody weeds on those aspects of biodiversity and ecosystem services that are important to the livelihoods of rural households; (ii) estimate the economic values that households place on the studied woody weeds and their impacts; and (iii) identify the measures that households take to mitigate the negative impacts. To address these objectives, context-based household questionnaires, focus group discussions and key informant interviews will be applied. Descriptive statistics and econometric models will be used for data analysis.

 

Theo Linders (CABI Switzerland) – This PhD thesis focuses on assessing the effects of two woody weeds, Lantana camara and Prosopis juliflora, on biodiversity and ecosystem services in East Africa. Data will be collected in the field along a cover gradient, in four regions in Ethiopia, Kenya and Tanzania. The effect of these woody weeds will be analysed for individual ecosystem services and for combined ecosystem services for each region. The effects will also be compared between the regions to look for regional and species-specific differences. Additionally, the ecological data will be combined with socio-economic data on the impacts of woody weeds in the same regions (see Ketema Bekele, above). This combination will allow an assessment of how the effects of invasive species on ecosystem services change with increasing cover of these woody weeds measured by both environmental and socio-economic data. It will therefore enable us understand the full impact of woody weeds  on the study area.

 

Hailu Shiferaw Desta (WRLC, Ethiopia) – The goal of this research is to spatially assess the historical and current, and to model the potential future distribution of Prosopis juliflora in Afar Region, Ethiopia. Based on these distribution maps, change in land use and land cover  will be mapped and quantified. Additionally, fractional cover maps of Prosopis juliflora will be generated. Based on identified key factors associated with invasion of Prosopis juliflora (elaborated based on the findings of the other PhD students as well as the entire project team), areas at risk of future invasion in Afar Region will be spatially predicted. In order to understand and quantify impacts on water, Prosopis tree water consumption will be measured at the plot scale. These measurements will then be spatially up scaled to district and regional level. Costs and benefits of above ground biomass ( as well as land use and management) will be spatially assessed and quantified.

 

Purity Rima Mbaabu (KEFRI, Kenya) – The goal of this research is to spatially assess the historical and current, and to model the potential future, distribution of Prosopis juliflora in Baringo County, Kenya. Based on these distribution maps, change in land use and land cover will be mapped and quantified. Additionally, fractional cover maps of Prosopis juliflora will be generated. This will be done with the help of spectro-radiometric field measurements. Also, when modelling the future spread potential of the species, different climate scenarios will be considered. Purity’s study set up is within the agro-pastoral communities in Baringo, situated along the Great Rift Valley in Kenya. In order to understand and quantify (spatial and monetary) impacts on biodiversity as well as agro-pastoral livelihoods she will work in close collaboration with other PhD students in the project team who assess these impacts on plot level and also conduct socio-economic household surveys. Besides that she will conduct participatory mapping exercises  in agro-pastoral communities. Costs and benefits of respective land cover and land use will be spatially mapped and quantified for the entire Baringo County.

 

Amina A Hamad (Sokoine University of Agriculture, Tanzania) – The research aims at assessing the distribution and abundance of Lantana camara in the East Usambara Mountains, Tanzania by using WorldView-3 satellite data as well as spectro-radiometric field measurements. Based on these mapping results, a fractional cover map of L. camara will be generated. Future potential invasions of L. camara shall be conducted by assessing historic L. camara distribution using a combination of aerial photos and participatory mapping. Furthermore, impacts of L. camara on plant species diversity and selected ecosystem services will be quantified and mapped by working in close collaboration with other PhD students who assess these impacts on field plot and household level. Their collected data will be used to upscale the impacts to the entire study area. Plot level work done by this PhD includes  field runoff experiments to quantify impacts of L. camara on soil loss and water quality.  As a result of the spectro-radiometric field work, this PhD research will establish a spectral library of important plant species (introduced as well as native) present in the study area. The data will then be used to further analyse their spectral separability.

Important knowledge about woody invasive species and how to manage them was shared at a stakeholder engagement workshop in Tanzania at the end of November 2015.

The workshop was held during a Woody Weeds project meeting in Amani Nature Reserve and local, regional and national stakeholders were invited to find out about the programme and have their say on how these invasive species affect livelihoods.

Around 30 stakeholders joined the project team, including the Tanga region commissioner, the Conservator of Amani Nature Reserve, the Director-General of the Tanzanian Forest Research Institute (TAFORI), as well as several village executives and village chairs.

In group exercises, participants shared knowledge about woody invasive species in the region and sustainable management techniques used to control them.

Workshop attendees also identified stakeholders that were seen as the most relevant for the management of woody weeds in Tanzania. These audiences were prioritised by considering how they were potentially able to help tackle the problem and their current engagement with the issue.

The meeting noted that some stakeholders may be unaware of the impacts the weeds have on livelihoods or currently not affected. The project and local stakeholders will work to engage with these important stakeholders in Tanzania to help improve the management of woody weeds.

We thank the participants in the workshop for their time and enthusiastic input, and look forward to future collaboration.

René Eschen, CABI

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The Baringo district northwest of Nairobi is one of the regions in Kenya where a number of mesquite species, Prosopis spp., were introduced some 40 years ago as part of poverty alleviation efforts. The trees were intended to provide, among other benefits, additional income.

Today Baringo is one of the most heavily invaded regions in eastern Africa, with severe consequences for the rural communities. As part of the kick-off meeting of the project the project team visited the district, one of the case study areas.

During this two-day visit, two communities were visited which suffered from high Prosopis invasion levels. These communities gave an interesting first insight into the dilemmas that have arisen due to Prosopis invasion. The first community we visited utilizes Prosopis for charcoal production and hopes to benefit in the future also from selling Prosopis wood to a local power plant; by utilizing this invasive species the community members gain some financial benefits and at the same time reduce the impacts of this plant on their land.

Irrespective of how the local communities deal with this invasive species, one of the main challenges in management is to find ways to slow down or reduce the spread of Prosopis and mitigate its negative impacts in Baringo (and elsewhere). While the government of Kenya supports local communities in utilizing Prosopis, there is, so far, little scientific evidence that utilization indeed slows down or even stops the spread of this aggressive invader.

One of the key tasks of the project will therefore be the evaluation of the impacts on the environment and rural livelihoods of the various management options against Prosopis and other woody invasive species, such as management by utilization, physical, chemical or biological control, or doing nothing, and to inform decision-makers about the key findings.

Urs Schaffner, CABI