Change of soil carbon storage in monoculture tree plantations across wide environmental gradients: Argentina as a case study

Forest plantations (through afforestation or reforestation) have been proposed as a valuable option to mitigate carbon (C) emissions. However, high spatiotemporal variation has been observed in soil organic carbon (SOC) pools associated to these systems. It has been proposed that SOC stock (Mg ha⁻¹) changes under forest plantations (ΔSOC) are related to the SOCstock in the natural system being replaced with positive ΔSOC in the sites with lowest initial SOCstock and negative ΔSOC in sites with initially high SOCstock. Although there is some debate related with statistical artifacts, the slope of this relationship may depend on environmental, biological and anthropic variables. In this context, we took advantage of a recent effort to quantify soil organic C stocks in forest plantations and contiguous land uses along 136 sites across a wide climatic and edaphic gradient in Argentina, South-America, to explore the patterns and drivers of SOC change due to this land-use change. We also added 183 data from a systematic bibliographic survey. Average ΔSOC of all the studied paired sites was low (average of -3.85 ±29.97 Mg ha⁻¹), with 57% of the paired sites showing a negative change. After applying a diagnosis method to detect statistical regression-to-the-mean bias and considering the pooled data and the different forest plantation groups (Pinusspp.,Eucalyptusspp.,Salicaceaespp, and native species), only Eucalyptusplantations showed a negative relationship betweenΔSOC and SOCstock in the control situation (i.e. a significant and negative impact on SOC in high-C soils). In general, most of the sites where forest plantations were introduced in Argentina have a relatively low baseline SOC (SOCstock