Future C loss in mid-latitude mineral soils: climate change exceeds land use mitigation potential in France

Many studies have highlighted significant interactions between soil C reservoir dynamics and global climate and environmental change. However, in order to estimate the future soil organic carbon sequestration potential and related ecosystem services well, more spatially detailed predictions are needed. The present study made detailed predictions of future spatial evolution (at 250 m resolution) of topsoil SOC driven by climate change and land use change for France up to the year 2100 by taking interactions between climate, land use and soil type into account. We conclude that climate change will have a much bigger influence on future SOC losses in mid-latitude mineral soils than land use change dynamics. Hence, reducing CO2 emissions will be crucial to prevent further loss of carbon from our soils.

The likeliness of the occurrence of cropland is generally highest on flat or gently sloping terrains. Moreover, in the South and East of France cropland tends to occur most frequently at lower altitudes and more in particular in the South-East of France on south orientated hillslopes. Equally, the probability to find grasslands is highest on flat or gently sloping terrains in mountainous areas in the East as well as on south oriented slopes in the South-East. Whereas the likeliness for the occurrence of forest is all over France highest on steep sloping terrains and more precisely on north orientated slopes in the South and East of France. In addition, in the North of France forest tends to occur mostly at higher altitudes while in the South of France this is at lower altitudes. The occurrence of vineyards and orchards in the North of France is highest on steeper slopes, while in the South this is highest at non-steep slopes at lower altitudes, with in general all over France a slight preference for south orientated slopes. Urban development has been found to occur most often at lower altitudes in the North and East of France and on non-steep sloping areas in the South-West, Centre and East of France (Fig. 1).

(ii) Climate (Fig. 2)
Croplands are most likely to be found in relatively dry areas in the Northern and Central parts of France and in relatively cool areas in the South, Eastern and Central parts of the country, whereas in the West and South-West of France croplands tend to occur more frequently under relatively humid and/or warm climatological conditions. Grasslands have in general the highest likeliness to occur in relatively humid and cool areas. Forest seems most likely to be found in relatively humid and warm areas, except for the West of France, where they are found in dry and cold areas. Vineyards and orchards generally occur in relatively dry areas (except in the most South-Eastern part of the country). In addition in the central part of France vineyards and orchards are more frequently found in relatively warm areas. The relation between the occurrence of urban land use and climate variables is unclear, although in the South-West, urban areas tend to be found more often in relatively warm areas (Fig. 2).
(iii) Soil Type (Fig. 3) Overall, the likeliness of occurrence of cropland tends to be highest on silty soils. In the West (except Brittany) croplands are less likely to be found on clay rich soils characterized by high bulk densities (e.g. alluvial plains of large rivers reaching coastal areas). In addition, in the more mountainous regions in France in the East and South-East (+ Brittany), croplands are more likely to be found on soils characterized by low stone contents, while in most other regions (not mountainous) this is the opposite (i.e. higher probability on soils with rather high stone content). The link between soil type and the spatial pattern of the probability of occurrence of grassland and forest is less clear. Nevertheless, the results indicate that grassland seems most often located on very fine textured soils (i.e. high clay content or low geometric mean particle size (Dg)) as well as on soils characterized by low stone content (especially in the North and Central part of France), whereas forests are more likely to be found on very fine textured soils (i.e. low Dg and high clay content) in the South-East of France and on more medium-fine -coarse textured soils in other regions (i.e. higher Dg and high silt content). In addition, forests appear more frequently on soils characterized by high stone contents in mountainous regions in the South-East of France as well as in the West, whereas in most other regions forests are more often located on soils characterized by low stone contents. Finally, vineyard and orchards are more likely to be found on soils characterized by high stone contents (South-East) and/or low clay contents (South of France).
The relationship between soil type and urban land use is unclear, although in general urban areas are found on soils characterized by high Dg (i.e. sandy soils), the latter can be observed in particular in the West of France (Fig. 3).
(iv) Socio economic (Fig. 4) Everywhere in France, unsurprisingly, urban areas have a high probability to be located in areas characterized by a high population potential, but nevertheless no clear overall trend roads. Furthermore, in the South-West forest are more likely to be found in areas characterized by low population potential but rather high employability potential.
Relationships between the considered socio-economic variables and the likeliness of occurrence of vineyard and orchards are less clear, although in the North, vineyard and orchards tend to be found closer to the main route and in the South further away from the main route (Fig. 4).

Validation
The resulting