Landscape Patterns and Modelling of Soil-Vegetation Relationship And

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY KUMASI, GHANA Landscape Patterns and Modelling of Soil-Vegetation Relationship and Related Ecosystem Services to Support Landscape Conservation in the Mo River Basin (Togo) by Badabaté DIWEDIGA (BSc. Natural Sciences, MPhil. Environmental Management) A Thesis submitted to the Department of Civil Engineering College of Engineering in partial fulfilment of the requirement for the degree of DOCTOR OF PHILOSOPHY in Climate Change and Land Use MAY 2016 DECLARATION I hereby declare that this submission is my own work towards the PhD degree in Climate Change and Land Use, and that, to the best of my knowledge, it contains no material previously published by another person, nor material which has been accepted for the award of any other degree of the University, except where due acknowledgment has been made in the text. Badabaté Diwediga (PG 8392712) ---------------------------- ---------------- Signature Date Certified by: Dr. Quang Bao Le CGIAR Research Program on Dryland 17 May 2016 Systems (CRP-DS) ------------------------ ----------------- International Centre for Agricultural Signature Date Research in Dry Areas (ICARDA) Amman 11195, Jordan. Prof. Sampson K. Agodzo Department of Agricultural Engineering ------------------------- ----------------- Kwame Nkrumah University of Signature Date Science and Technology (KNUST). Kumasi, Ghana Prof. Kpérkouma Wala Laboratory of Botany and Plant 17 May 2016 Ecology -------------------------- ---------------- Department of Botany Signature Date University of Lomé Lomé, Togo. Prof. Yaw A. Tuffour ------------------------ ------------------ Head of Department Signature Date i ABSTRACT In order to support integrated landscapes and restoration efforts, this research focused on the assessment and monitoring of the spatio-temporal land use/cover change (LUCC) and degradation in the Mo River Basin (a subunit of the Volta basin of about 1,490 km2 in Central Togo). Field measurements, legacy and ancillary data were subjected to sequential multivariate methods, correlation analyses, geostatistics and modelling to analyse landscape conditions. First, along a gradient of land protection regime, data from extensive soil sampling and forest inventory were used to analyse soil organic carbon (SOC) and total nitrogen (TN) storage up to 30 cm depth, and the interactions between vegetation-soil conditions. Next, Landsat images of 1972, 1987, 2000 and 2014 combined with most updated global topographic and soil databases were used to analyse the landscape changes and its impacts on SOC, TN, soil loss potential and landscape patterns. Finally, the Landscape Management and Planning Tool adapted for the Mo basin (LAMPT_Mo), a spatially explicit model based on the Revised Universal Soil Loss Equation (RUSLE), was used to model the historical soil loss, and evaluate the efficiency of some land management scenarios. Different databases and field characterisation were used for model calibration and validation. The results showed that SOC and TN varied significantly according to land use/cover types, soil depths, topographical positions and land protection regime. With forests and woodlands exhibiting highest amounts of nutrients, mean TN varied from 0.06 to 0.16 % in the topsoil (0 – 10 cm) and 0.04 to 0.09 % in the subsoil (10 – 30 cm). Similarly, SOC ranged from 1.81 % in farmlands to 3.58 % in forests in the topsoil while woodlands had highest SOC in the subsoil (2.23 %). The river basin is made up of four and three vegetation types in unprotected and protected areas, respectively. The synergized effects of land protection status, soil conditions, landform, and human disturbances drive these vegetation patterns. From the historical analyses, natural lands dominated the basin, ii though their area constantly decreased since 1972. Contemporary LUC (in 2014) is dominated by savannahs/shrubs (53 %), woodlands (27 %) and forests (11 %). Non- cultivated and vegetation regrowth areas were the most dominant of the LUCC trajectories to whom SOC, TN and soil loss potential were responsive. Trajectories of land cover decline induced soil quality deterioration while correlation analyses showed soil loss to be more landform-driven than LUCC. Simulations using LAMPT_Mo yielded values of net soil loss (NSL) far higher than the tolerable limits for the Tropics. NSL markedly changed over time with about 26, 23, 27 and 44 Mg ha-1y-1, for 1972, 1987, 2000 and 2014, respectively. Steep slopes (≥ 15 ᴼ), poorly covered lands, and riversides (distances ≤ 100 m) are critical areas of sediment source. Some intervention measures such as controlling erosion hotspots through LUC protective measures could help reducing NSL up to 70 %, to the tolerable limits for the Tropics. The combination of methods and approaches used for the monitoring and assessment of landscape change and degradation enabled to capture the different spatial aspects of the problem of land degradation in the Mo basin. The study demonstrated that important appropriate conservation measures would be necessary for the catchment rehabilitation, protection and sustainable resource use. iii TABLE OF CONTENTS DECLARATION ............................................................................................................ i ABSTRACT ................................................................................................................... ii LIST OF FIGURES ...................................................................................................... vii LIST OF TABLES ...................................................................................................... viii LIST OF ABBREVIATIONS ....................................................................................... ix ACKNOWLEDGEMENTS .......................................................................................... xi CHAPTER 1: GENERAL INTRODUCTION ............................................................... 1 1.1. Background ............................................................................................................. 1 1.2. Problem statement ................................................................................................... 2 1.2.1. National and local challenges of land degradation............................................... 2 1.2.2. Research approach to address multifaceted knowledge needs for sustainable land management and restoration in the Mo basin................................................................. 3 1.3. Research objectives ................................................................................................. 5 1.4. Outline of the Thesis ............................................................................................... 5 CHAPTER 2: LITERATURE REVIEW ....................................................................... 6 2.1. Concepts and definitions ......................................................................................... 6 2.2. Phenomenon of land degradation and causes .......................................................... 8 2.3. Land use/cover change and land degradation ......................................................... 9 2.4. Vegetation patterns as impacted by various drivers .............................................. 12 2.5. Land degradation and soil erosion ........................................................................ 13 2.6. Approaches for modelling ESS dynamics ............................................................. 16 2.7. Landscape restoration and implications for climate change ................................. 17 CHAPTER 3: STORAGE AND DRIVERS OF SOIL ORGANIC CARBON AND TOTAL NITROGEN IN MO LANDSCAPES ........................................................... 19 3.1. Introduction ........................................................................................................... 19 3.2. Material and methods ............................................................................................ 20 3.2.1. Study area ........................................................................................................... 20 3.2.2. Sampling design and soil sample collection ...................................................... 22 3.2.3. Laboratory analyses of soil samples................................................................... 23 3.2.4. Collection of in-situ ecological and other environmental variables ................... 24 3.2.5. Mapping of the spatial patterns of SOC and TN contents ................................. 27 3.2.6. Statistical analyses.............................................................................................. 27 3.3. Results ................................................................................................................... 28 3.3.1. Variations of SOC and TN under different land use/cover types ...................... 28 3.3.2. Distribution of SOC and TN according to topographical positions ................... 31 3.3.3. Influence of land protection regime on soil chemical properties ....................... 33 3.3.4. Interactions between soil properties and environmental variables..................... 35 3.3.5. Soil chemical properties-environment interactions in agro-systems .................. 39 3.3.6. Spatial distribution of TN and SOC in the Mo basin ......................................... 42 3.4. Discussion ............................................................................................................

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