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A high-resolution spatially-explicit methodology to assess global soil organic carbon restoration potential21 March 2017Luuk Fleskens, Michel Bakkenes, Coen Ritsema, Ben ten Brink, Klaas Oostindie, Gudrun Schwilch
Rationale Urgent need for spatial data to guide initiatives on
restoration and prevention of land degradation: what practices are available, possible and feasible in each location, and how do they perform?
Much research exists on restoration opportunities, but the bulk of it concentrates on local scales.
A new approach is therefore much needed that, based on the state of knowledge, enables a global outlook on opportunities and challenges of SOC restoration.
Methodology
We model the global SOC restoration potential in the top 30-cm of soil as a full-scale SOC Restoration scenario by aggregating the effects of the most effective restoration category in each location.
SLM and reforestation practices can affect SOC in two ways:Restoring SOC and Preventing SOC loss
Establishing SOC restoration potential requires: i) restoration and prevention trend lines considering time
after investment (literature review)ii) SOC restoration ceilings (S-World)iii) Current levels of soil loss and SOC loss (NDVI+S-World) iv) Classification of restoration measures and developing an
allocation mechanism for these categories of restoration measures (WOCAT and data review)
C Sequestration potential: restoration + prevention of SOC losses
SLM effect on SOC – relation of SOC increase with timeLiterature reviewRelationship between the number of years and the increase of Soil Organic Carbon (SOC)(Mg/ha) for those cases exhibiting a sequestration rate greater or equal than 0.25 Mg/ha, or where the total SOC increase is greater or equal than 7.5 Mg/ha
This function is used to map C restoration potential
Current SOC levels, trend and potential SOC content30 arcsec (~1 km2) global datasets:• Current soil organic carbon (SOC) content
Based on S-World; functional interpolation modelling based on harmonised global soil profiles. Stoorvogel et al. (2017a) Land Deg Dev in press)
• Current rate of soil degradation (SOC loss and soil depth loss) Based on trend analysis and projection of bias-corrected NDVI analysis. Schut et al. (2015) PLOS One 10(10): e0138013
• Potential soil organic carbon (SOC) content Based on S-World; analyses of soils under natural land use classes and best possible agricultural management given current land use. Stoorvogel et al. Stoorvogel et al. (2017b) Land Deg Dev in press)
SLM category typesWOCAT Broad
CategoriesWOCAT
Sub-classifications
WOCAT Broad categories
Categorisation used (number of practices included)
Agronomic
Cropping management
Conservation agriculture
Reduced tillage (44)
Soil improvement
Manuring/composting Soil improvement (42) Integrated soil fertility management
Vegetative
Cover crops Vegetative cover (33) Cross-slope barriers (vegetative)
Vegetative barriers (43)
Agroforestry Agroforestry (38) Sustainable planted forest management
Reforestation in savannahs* (29) Assisted natural regeneration* (6) Smallholder woodlots* (6) Forest plantations *(6)
Structural
Water management
Water harvesting
Floodwater harvesting Water harvesting (36)
Macrocatchment Microcatchment Rooftop/courtyard
Irrigation
Drip irrigation Irrigation (24) Smallholder irrigation
management Cross-slope barriers (structural)
Terraces Terracing (29) Bunds Bunds (45)
Gully rehabilitation Gully rehabilitation (26) Management
Grazing land management
Integrated crop-livestock management
Grazing land management (39)
Pastoralism and rangeland management
Forest management
Sustainable forest management in drylands Sustainable rainforest management
Combination
Miscellaneous
Other Multi-faceted intensification (19)
Trends and opportunities
Classification used
SOC restoration potential per technology category*
*Based on WOCAT expert opinion, assuming a 5-year assessment lag period
SOC Increase (%)Soil loss reduction (%)
Applicability of SLM categories (examples)
Agroforestry
Terraces
Water harvesting
Bunds
Considering land use, slope, elevation, precipitation, biome, soil depth, soil texture, population density, distance to roads/ports/etc (at 1 km2 resolution)
Most effective restoration technology per location/pixel
Soil organic carbon restoration potential until 2050
SOC restoration potential 2050
Calculations based on following assumptions:
• Excludes conversion of any agricultural land to forest• Considers only the top 30 cm of soil as responding to
management
Total global SOC restoration and prevention: 22 Gt C
Conclusions1. We present a first, high resolution (30 arc second) and
spatial-explicit assessment of the global SOC restoration potential.
2. A theoretical full-scale Restoration scenario considering both restoration of historical and prevention of ongoing SOC losses, amounts to 22 Gt by 2050.
3. Comparing our results to findings by others, the potential contribution of SOC restoration to climate change mitigation is low, mainly governed by SOC ceilings associated to current land use.
4. A variety of restoration technologies can be deployed for restoration. There are some interdependencies that were not considered (e.g. use of compost/manure may be limiting; livestock exclusion may lead to degradation surrounding areas)