Combining Earth Observation, Socio-Economic Surveys, and Spatial Modelling to Evaluate Ecosystem Services Bundle in Selected Landscapes of North-Eastern Mountains, Tanzania

Abstract

The mountainous environments of NE Tanzania are of international relevance for safeguarding biodiversity, sequestering carbon and delivering important ecosystem services (ES) to local populations. However, these landscapes are also particularly vulnerable to land degradation due to steep slopes, fragile soils, increasing population, severe shortages of pastureland, and climate change. Hence, with population densities as high as 650 people/km2 in the highlands, and with smallholder agriculture as the main income-generating activity finding a nexus between sustainability and ES delivery and the urgent short-term economic needs of households is an important challenge. The overarching goal of this doctoral thesis is to establish a guideline framework for understanding the role of indigenous agroforestry systems in delivering ES bundle aims to enhance their long-term sustainability while finding common ground between conservation efforts and the livelihoods of rural communities. The focus was on four smallholder indigenous agroforestry systems (AGF) in mountainous landscapes in the NE Mountains of Tanzania: Kihamba (Mount Kilimanjaro), Ginger (Pare Mountains), Miraba (West Usambara Mountains) and Mixed spices (East Usambara Mountains). These landscapes form a distinct climate transect, characterised by varying altitudes, rainfall patterns, soil types, and vegetation. Publications I and II use a simple stratification approach by subdividing mountainous landscapes into equal-size study landscape boxes of 200 km2. In each box, six wards (local administrative units) were selected purposefully to characterize and describe the salient features of most common AGF practices by smallholder farmers along transects. A combination of various approaches and techniques, including earth observation, benefit transfer method (BTM) model, field and socio-economic surveys and individual-based statistical methods for the valuation of ES provision from AGF were employed. Publication III assesses the potential and variability of AGF in sequestering carbon and promoting soil fertility by field soil surveys and laboratory analyses. Publication IV evaluates vulnerable group access (i.e., availability and adequacy) to different ES by socio-economic surveys. In publication V the spatial prediction of ES tradeoffs and synergies potential in the AGF was simulated based on regenerative and degenerative scenarios using a spatial system dynamics model. Publication I reveal that Mt. Kilimanjaro has the highest delivery of ES. However, a noticeable loss in ES is evident in Mt. Kilimanjaro and the South Pare Mts. agroforestry signalling a decline that can significantly impact the livelihoods of communities that rely on highland landscapes for various ES provisioning. Additionally, the increase in ES from forests has not been sufficient to offset the losses observed in agroforestry. These findings highlight that programs promoting restoration of agroforestry can be successful yet are not sufficient for increasing overall tree cover in the studied landscapes. Publication II, moreover, highlights that within the AGF systems, the native tree cover has been partly replaced by non-native trees in Kilimanjaro and Pare, while native trees have been severely degraded in the West and East Usambara AGF systems. Concerning smallholder farmers' decision-making process across the four study landscapes, the farmers recognise the intrinsic value of native tree species. Their socioeconomic realities force them to prioritise economically significant ES delivery when selecting trees. Specifically, they tend to favour trees that support cash crops, food production, fuel, timber, fodder, or provide shade for coffee. These findings highlight alarming land use/cover changes and degradation within agroforestry ecosystems, underscoring the urgent need for frameworks that mitigate the adverse impacts while balancing development and restoration efforts with the provision of economic needs and ecosystem services. In publication III, the evidence base was built for the potential benefits of native trees for carbon sequestration and soil fertility improvement in AGF, contributing to climate change mitigation and adaptation. The findings show that the highest soil carbon sequestering potential was found in the old Kihamba systems (located on Nitisols) of Mt. Kilimanjaro compared to other systems on Acrisols of the Pare, West and East Usambara Mts. which calls for soil management practices and restoration strategies that have significant potential for optimizing the soil carbon and fertility. Next, publication IV determine who suffered most from losses in ES delivery upon landscape degradation. Degraded landscapes also become less inclusive and vulnerable groups in society, i.e. single-headed households, including female-headed households and persons living with disabilities, are unequally affected by the observed degradation, as they most of all rely on access to ES closer to their homes. The underlying drivers of this degradation, which create imbalances between conservation efforts and livelihoods, are the topic of publication V. From the dynamic model analysis applied, it is evident that farmers will require additional support and incentives to maintain native trees in their fields. This support could come from government and NGO campaigns and should be inclusive and tailored to local needs. It reveals a clear dichotomy between sustainably managed and degraded agroforests, with the future of these systems depending on the ability to transition from degeneration to regeneration. The findings of this research provide evidence across landscapes for addressing challenges and generating opportunities for the socio-ecological ecosystem services nexus in AGF in tropical mountains:Declaration of conformity................................................................................ ii Declaration of Independent Work and Consent ............................................ iii Thesis at a Glance ........................................................................................ v Graphical abstract (a) ................................................................................... vii Graphical abstract (b) ................................................................................... viii Abstract ......................................................................................................... ix PART A: SYNTHESIS.......................................................................................1 1. INTRODUCTION .........................................................................................1 1.1 Tropical Mountain Landscapes ..................................................................1 1.2 Ecosystem Services Bundle.......................................................................3 1.3 Agroforestry Systems..................................................................................5 1.3.1.1 The genesis and evolution of indigenous agroforestry systems (Drawing from the past, adapting to the future) ................................................5 1.3.1.2 Strength through diversity .................................................................... 6 1.3.1.3 Socio-cultural aspects of AGF evolution .............................................. 8 1.3.1.4 Success and setbacks ......................................................................... 9 1.3.1.5 Historical impact and evolution in Sub-Sahara Africa ..........................10 1.4 Research Questions and Objectives ..........................................................15 1.4.1 Degenerative scenario .............................................................................15 1.4.2 Regenerative scenario ............................................................................ 16 2. MATERIAL AND METHODS ........................................................................ 17 2.1. Study area ................................................................................................. 17 2.2 Overview and Critical Reflections of Methods Applied................................ 18 3. SYNTHESIS OF RESULTS AND DISCUSSION .......................................... 22 3.1 Indigenous Agroforestry Systems, Biodiversity Conservation, and Ecosystem Services Bundle (Publication I, II) ............................................................... 23 3.2 Indigenous Agroforestry Systems on Degradation and Climate-smart Solutions (Publication III)............................................................................................. 27 3.3 Indigenous Agroforestry Systems and Inclusivity (Publication IV) ............. 31 3.4 A System Dynamics Modelling: A Framework for Evaluating Ecosystem Services bundle (Publication V)................................................................................. 32 3.4.1 Trade-offs, synergies, and provision potentials in tropical mountain landscapes................................................................................................32 3.4.2 Trends and behaviours from the system dynamic model ........................ 33 3.4.3 Widening all bottlenecks in the conduit to sustainability........................... 35 4. CONCLUSION AND RECOMMENDATIONS ............................................... 36 5. PERSPECTIVES FOR FURTHER RESEARCH .......................................... 39 REFERENCES ................................................................................................. 40 Acknowledgments ............................................................................................. 55 PART B: PUBLICATIONS ................................................................................. 58 PUBLICATION I ................................................................................................ 60 PUBLICATION II ............................................................................................... 98 PUBLICATION III .............................................................................................. 117 PUBLICATION IV .............................................................................................. 131 PUBLICATION V ............................................................................................... 152 List of Figures Figure 1: Ecosystem services and their link to human well-being (ES Bundle).... 4 Figure 2: Indiscriminate logging for subsequent coffee cultivation in NE Tanzania during the German colonial period before World War I........................................ 11 Figure 3: Location of the studied NE mountain landscapes of Tanzania............. 18 List of Tables Table 1: The historical evolution of agroforestry systems in Sub-Saharan Africa...13 Table 2: Historical transformation of Indigenous Agroforestry Systems in mountains regions of NE Tanzania ..........................................................................................1