Prosopis juliflora management and grassland restoration in Baringo County, Kenya: Opportunities for soil carbon sequestration and local livelihoods

1. Climate change, land degradation and invasive alien species (IAS) threaten grassland ecosystems worldwide. IAS clearing and grassland restoration would help to reduce the negative effects of IAS, restore the original vegetation cover and sustain livelihoods while contributing to climate change mitigation, but uncertain financial benefits to local stakeholders hamper such efforts. This study assessed where and when net financial benefit could be realized from Prosopis juliflora management and subsequent grassland restoration by combining ecological, social and financial information. 2. Impacts of Prosopis invasion and grassland degradation on soil organic carbon (SOC) in nine sublocations in Baringo County, Kenya, were evaluated. Then the financial impacts of Prosopis removal and grassland restoration in the area were calculated and spatially explicit management scenarios for each sublocation modelled, combining geographical information derived from satellite images taken in different years of the invasion with SOC data and socio-economic data collected in the sublocations. 3. The expanding Prosopis distribution and density since 1995 have increased cumulated SOC storage on former bare land or degraded grasslands. On former pristine or restored grasslands, however, Prosopis invasion has reduced total SOC storage. 4. Prosopis removal and grassland restoration are predicted to yield financial benefits through charcoal made from removed trees, increased cattle numbers and carbon credits. However, a trade-off between increased SOC and net financial benefit was found. The predicted net SOC increase would contribute around one-tenth, at most, to the net financial benefit. 5. The available budget, based on Baringo households’ average willingness to pay, would enable removal, on average, of one-fifth of Prosopis per sublocation in a single year. A larger area can be cleared if Prosopis is sparse than if it is dense. The analyses show that in some sublocations, households’ annual investments could result in restoration of all former grassland areas. 6. Synthesis and applications. This study shows how integrating and linking detailed ecological, social and financial geodata to develop accurate and realistic invasive alien species management scenarios can illustrate costs and benefits of management interventions in a spatial context. Such scenarios should be used more extensively to support land management decisions

Pathways towards the Sustainable Management of Woody Invasive Species: Understanding What Drives Land Users’ Decisions to Adopt and Use Land Management Practices

Sustainable land management (SLM) practices are key for achieving land degradation neutrality, but their continued implementation lag behind the progression of various forms of land degradation. While many scholars have assessed the drivers of SLM uptake for restoring land affected by desertification, drought, and floods (SDG 15.3 and partly SDG 2.4), little is known about the implication of SLM implementation on invasive alien species (IAS) management. This study aimed at understanding the challenges and proposing solutions for the uptake of SLMs with respect to the management of the invasive tree, Prosopis juliflora, in Baringo County, Kenya. Data were collected with semi-structured questionnaires, the responses were coded into themes, and c-coefficient tables were used to determine code linkages. Our results show that the availability of incentives is the main motivation for invasion management. Thus, management efforts have often focused on private parcels, while communally shared lands tended to be neglected despite their vulnerability to invasion. We conclude that sustainable IAS management lies at a landscape scale, and thus the national IAS management strategies should adopt a collective approach by empowering local actors to engage in SLM implementation

Sustainable Management of Rangelands: An Assessment of Invasion Cover Trajectories and Their Contribution to Invasion Management in Marigat Sub-County, Kenya

Invasive alien species have complex spatiotemporal patterns of spread beyond geographical and jurisdictional boundaries. This calls for a coordinated management approach that is spatially explicit, extends beyond individual plot levels, and incorporates land users’ perceptions and decisions. This study, therefore, aims at assessing spatiotemporal invasion trajectories of the invasive tree Prosopis juliflora in Baringo County, Kenya, and evaluating their possible relation to land users’ management decisions. Pre-classified land cover data over a seven-year time period (1988–2016) were reclassified based on the presence or absence of P. juliflora and integrated into ArcGIS to produce P. juliflora cover trajectories for analysis. The spatiotemporal analysis of Prosopis invasion dynamics yields trajectories that can be linked to underlying land users’ management decisions. Areas that remained free of Prosopis since their first clearance were primarily areas where the invasion would cause the highest loss in terms of income or opportunity costs; areas that were never cleared since they were first invaded tended to be areas where no one could be personally held accountable for their management, while the abandonment of management followed by re-invasion appeared to be linked to different drivers, including diversification of livelihoods and lower market prices for horticultural products. Our findings indicate that invasion trajectories are useful in informing existing management strategies to adopt context-based invasive species management practices. The study recommends scaling up the trajectory analysis approach to be replicated in large-scale invasion management strategies. Since it requires considerable finances and time to conduct such analyses on raw satellite imagery, we suggest further research on how to simplify the approach to make it easily and efficiently replicable for large-scale applications

Restoration of degraded grasslands, but not invasion by Prosopis juliflora, avoids trade-offs between climate change mitigation and other ecosystem services

Grassland degradation and the concomitant loss of soil organic carbon is widespread in tropical arid and semi-arid regions of the world. Afforestation of degraded grassland, sometimes by using invasive alien trees, has been put forward as a legitimate climate change mitigation strategy. However, even in cases where tree encroachment of degraded grasslands leads to increased soil organic carbon, it may come at a high cost since the restoration of grassland-characteristic biodiversity and ecosystem services will be blocked. We assessed how invasion by Prosopis juliflora and restoration of degraded grasslands in a semi-arid region in Baringo, Kenya affected soil organic carbon, biodiversity and fodder availability. Thirty years of grassland restoration replenished soil organic carbon to 1 m depth at a rate of 1.4% per year and restored herbaceous biomass to levels of pristine grasslands, while plant biodiversity remained low. Invasion of degraded grasslands by P. juliflora increased soil organic carbon primarily in the upper 30 cm and suppressed herbaceous vegetation. We argue that, in contrast to encroachment by invasive alien trees, restoration of grasslands in tropical semi-arid regions can both serve as a measure for climate change mitigation and help restore key ecosystem services important for pastoralists and agro-pastoralist communities

Factors enhancing the level of utilisation of research knowledge on ecosystems

The significant resource investment in research on ecosystems for development of the Global South does not necessarily result in high levels of research knowledge utilisation (RKU). Understanding the factors associated with various levels of RKU can inform funding agencies and researchers developing new projects. We applied a combination of a questionnaire survey and follow up interviews with members of research teams of multiple, broadly comparable projects to make an assessment of achieved RKU levels using a combination of quantitative statistical hypothesis testing and narrative description of survey responses. Research knowledge dissemination by members of the project team who work for non-academic institutions or champions, e.g. particularly motivated people that promote and facilitate implementation or adoption of the project results, and via television was associated with higher research knowledge utilization. By contrast, dissemination by members of the project team working for academic institutions and via peer-reviewed journals was associated with lower RKU. The achieved level of RKU was consistently lower than the targeted level of RKU across spatial scales. The discrepancy between the perceived level of RKU and the evidence provided by survey respondents indicates the need for better monitoring the utilisation of research knowledge in development pathways. Our results further suggest that three years project duration is too short to achieve high levels of RKU in socio-ecological systems. We recommend involvement of non-academic members of the project team in project design, leadership and dissemination for increasing RKU.ISSN:1932-620

Spatiotemporal trajectories of invasive tree species reveal the importance of collective action for successful invasion management

Biological invasions are complex processes requiring coordinated and spatially targeted management. This study assessed spatiotemporal trajectories and determinants of Prosopis cover in Baringo County, Kenya. Land cover data for every seven years between 1988 and 2016 revealed the presence of Prosopis. We tested for trajectory clusters using spatial autocorrelation and overlaid the trajectory categories with landscape features. Generally, most plots were only temporarily managed or not managed at all, while continuous management of Prosopis occurred mainly near rivers and on plots suitable for cultivation. Parcels within 250 m from roads, which are dispersal pathways for Prosopis seeds, were rarely cleared of Prosopis. We conclude that successful management requires incentives for stakeholders’ engagement in collective management action at a landscape level. Trajectory mapping should be integrated into planning tools to foster the prioritization of timely and context-specific response mechanisms

Niche change analysis as a tool to inform management of two invasive species in Eastern Africa

Significant progress has been made in providing guidelines and recommendations for assessing theecological niche, stage of invasion, and probability of invasive alien plant species (IAPS) potential distribution inspace and time. We followed these recommendations by developing and comparing ordination and species dis-tribution models (SDMs) of two important woody IAPS in Eastern Africa,Prosopis julifloraandLantana camara,and interpreting the results to inform IAPS management. The two species differ in their invasion history in East-ern Africa; whileL. camarawas widely introduced there in the 19th century,P. juliflorawas only planted atselected locations in the 1970s and 1980s. For the SDMs, machine learning algorithms were used to generate oneensemble model each forP. julifloraandL. camara. For ordination, we used bioclimatic variables, performed aprincipal component analysis, and compared the native and global niches of the species with the Eastern Africanniche. Niches varied substantially depending on the percentage of marginal climates excluded from the models.Additional analysis ofthe local niches surrounding the originalP. julifloraplantations showed that they are com-plementary, which may have led to anoverestimation of regional nichefilling. While niche expansion was absentor small depending on the percentage of marginal climates excluded, analysis of the stages of invasion suggestedthatP. julifloramay have started to adapt to novel climatic conditions and thatL. camarais approaching apseudo-stable equilibrium in Eastern Africa. The SDMs showed that large areas in Eastern Africa that have notyet been invaded byP. julifloraare suitable or will become suitable with climate change. ForL. camara,theglobalSDM predicted a considerably larger suitable area than the Eastern African one, raising uncertainty about theareas to be included in a regional management strategy. Thus, combining ordination and SDMs and integratinga geographic component into ordination is useful in assessing IAPS invasion stages and potential niche shifts,and the results help inform IAPS policy and management. The combined approach can also serve to guideexperimental studies addressing divergences betweenresults generated with the different approaches

Spatial Evolution of Prosopis Invasion and its Effects on LULC and Livelihoods in Baringo, Kenya

Woody alien plant species have been deliberately introduced globally in many arid and semi-arid regions, as they can provide services and goods to the rural poor. However, some of these alien trees and shrubs have become invasive over time, with important impacts on biodiversity, ecosystem services, and human well-being. Prosopis was introduced in Baringo County, Kenya, in the 1980s, but since then, it has spread rapidly from the original plantations to new areas. To assess land-use and land-cover (LULC) changes and dynamics in Baringo, we used a combination of dry and wet season Landsat satellite data acquired over a seven-year time interval between 1988−2016, and performed a supervised Random Forest classification. For each time interval, we calculated the extent of Prosopis invasion, rates of spread, gains and losses of specific LULC classes, and the relative importance of Prosopis invasion on LULC changes. The overall accuracy and kappa coefficients of the LULC classifications ranged between 98.1−98.5% and 0.93−0.96, respectively. We found that Prosopis coverage increased from 882 ha in 1988 to 18,792 ha in 2016. The highest negative changes in LULC classes were found for grasslands (−6252 ha; −86%), irrigated cropland (−849 ha; −57%), Vachellia tortilis-dominated vegetation (−3602 ha; −42%), and rainfed cropland (−1432 ha; −37%). Prosopis invasion alone directly accounted for over 30% of these negative changes, suggesting that Prosopis invasion is a key driver of the observed LULC changes in Baringo County. Although the management of Prosopis by utilization has been promoted in Baringo for 10−15 years, the spread of Prosopis has not stopped or slowed down. This suggests that Prosopis management in Baringo and other invaded areas in East Africa needs to be based on a more integrated approach

The impact of invasive species on social-ecological systems: Relating supply and use of selected provisioning ecosystem services

Understanding the sustainability of social-ecological systems requires quantifying the relationships between ecosystem service supply and use. However, these relationships, and the influence of environmental change on supply and use, are poorly known. Here we apply a nested sampling design to analyse supply-use relationships in ten administrative units in each of two Eastern African regions undergoing invasion by an alien tree, Prosopis juliflora. Ecological data on supply of two key provisioning services, woody and herbaceous biomass, were collected in field plots and the use, defined here as income and livestock numbers, was assessed using household surveys. Supply and use were then up-scaled to the level of the smallest administrative unit. High Prosopis cover affected the supply of both services, with increased woody biomass but reduced herbaceous biomass. We found that supply of woody biomass was positively associated with income from wood sales. Prosopis invasion reduced income from livestock and slightly decreased cattle numbers over the past ten years. We propose that biophysical and socio-economic data collected at the same scale can help to determine supply-use relationships for ecosystem services and we discuss how integration of supply-use data can inform sustainable management of social-ecological systems in the context of environmental change