Biophysical and socioeconomic factors influencing soil carbon stocks: a global assessment

Soil is the most important terrestrial carbon (C) reservoir but is greatly impacted by land use change (LUC). Previous analyses of LUC impacts on soil C have focused on biophysical variables, leaving aside the influence of socioeconomics. The aim of our study was to determine global soil organic carbon (SOC) change patterns after LUC and to assess the impacts of both biophysical and socioeconomic factors that influence stocks of SOC after LUC simultaneously. This was done at a global scale using 817 sites from 99 peer-reviewed publications. We performed separate analyses for cases in which there were gains and losses of SOC. The best predictors of SOC stock changes were the type of LUC and predictors related to sampling depth, climate, biome, soil order, relief, geology, years since LUC, and primary productivity. However, also, socioeconomic variables such as indices of poverty, population growth, and levels of corruption were important. They explained 33% of the variability in SOC on their own and helped improve model accuracy from 42 to 53% when considered in combination with biophysical variables. SOC losses were highly correlated to the type of LUC and social variables, while SOC gains correlated most strongly with years since LUC and the biophysical variables. The analyses confirm that one of the biggest drivers of SOC loss is conversion to agroindustrial scale cropping, whereas with regard to the recuperation of SOC after LUC, the factor “time since conversion” emerged as the most important predictive variable, which must be better integrated in respective policy expectations. We conclude that policies should more than ever incentivize holistic approaches that prevent additional loss of native SOC, while at the same time promoting sustainable intensification of existing agricultural regions. Finally future investments on LUC to regain SOC should be aligned with efforts to alleviate poverty and corruption for their potential to achieve mutual gains in soil fertility and socio-economic parameters.