Soil organic carbon baselines for land degradation neutrality : Map accuracy and cost tradeoffs with respect to complexity in Otjozondjupa, Namibia
Nijbroek, Ravic ; Piikki, Kristin ; Söderström, Mats ; Kempen, Bas ; Turner, Katrine G. ; Hengari, Simeon ; Mutua, John - \ 2018
Sustainability 10 (2018)5. - ISSN 2071-1050
Land degradation neutrality - Map accuracy - Method complexity - Namibia - Sampling density - Soil organic carbon
Recent estimates show that one third of the world's land and water resources are highly or moderately degraded. Global economic losses from land degradation (LD) are as high as USD $10.6 trillion annually. These trends catalyzed a call for avoiding future LD, reducing ongoing LD, and reversing past LD, which has culminated in the adoption of Sustainable Development Goal (SDG) Target 15.3 which aims to achieve global land degradation neutrality (LDN) by 2030. The political momentum and increased body of scientific literature have led to calls for a 'new science of LDN' and highlighted the practical challenges of implementing LDN. The aim of the present study was to derive LDN soil organic carbon (SOC) stock baseline maps by comparing different digital soil mapping (DSM) methods and sampling densities in a case study (Otjozondjupa, Namibia) and evaluate each approach with respect to complexity, cost, and map accuracy. The mean absolute error (MAE) leveled offafter 100 samples were included in the DSM models resulting in a cost tradeofffor additional soil sample collection. If capacity is sufficient, the random forest DSM method out-performed other methods, but the improvement from using this more complex method compared to interpolating the soil sample data by ordinary kriging was minimal. The lessons learned while developing the Otjozondjupa LDN SOC baseline provide valuable insights for others who are responsible for developing LDN baselines elsewhere.
Development of a Soil Organic Carbon Baseline for Otjozondjupa, Namibia
Nijbroek, R. ; Kempen, B. ; Mutua, J. ; Soderstrom, M. ; Piikki, K. ; Hengari, S. ; Andreas, A. - \ 2017
In: Proceedings of the Global Symposium on Soil Organic Carbon 2017. - FAO - ISBN 9789251098387 - p. 142 - 150.
Land Degradation Neutrality (LDN) has been piloted in 14 countries and will be scaled up to over 120 countries. As a LDN pilot country, Namibia developed sub-national LDN baselines in Otjozondjupa Region. In addition to the three LDN indicators (soil organic carbon, land productivity and land cover change), Namibia also regards bush encroachment as an important form of land degradation. We collected 219 soil profiles and used Random Forest modelling to develop the soil organic carbon stock baseline. Values range between 0.53 and 4.27 kg/m2 in the sandy Otjozondjupa soils. LDN baselines were integrated into other national planning processes to add value to LDN products. Analyses of the relationship between soil carbon and land cover change, especially from grassland to bushland, increased the usefulness of soil carbon maps for the Integrated Regional Land Use Planning process. Local ownership of LDN baseline development, from data collection to digital soil mapping, was crucial for local stakeholders.