Spatio-temporal analysis of soil moisture variations explains the tree-growth decline of multiple species in Mediterranean
Soil moisture (SM) is a crucial variable to the energy balance between the soil and the atmosphere. Given the lack of long-term instrumental SM measurements, information captured by satellites and climate reanalysis emerges as a useful tool. In the Mediterranean ecosystems of Chile (MC; 30°-36°S), several studies have reported a forest decline mainly associated with a persistent mega-drought (MD) during the last decade. We evaluated the main spatio-temporal patterns of tree growth during 1962-2015 performing a PCA and utilizing 35 tree-ring chronologies of 11 tree species growing across the MC. In addition, we study their relationships performing Pearson correlations with SM during 1980-2015 and from three sources (ESA-CCI, GLEAM v3.5, and the skin reservoir contained SRC ERA5-Land). Results show that PC1 explained 39% of the total variance of tree growth, while PC2 and PC3 capture 10% and 8%, respectively. PC1 captures a regional tree-growth signal and exhibits a decrease since 2007. The temporal relationships between PC1 and all SM products exhibited a significant strong relationship during the entire calendar year, reaching the highest values with GLEAM and SRC products. Significant correlation values between 0.4 to 0.9 were found with both products. Furthermore, correlations between -0.5 to 0.67 were recorded using SM ESA-CCI. A regional mean SM time series derived by the annual average of the GLEAM and SRC products covering the entire MC revealed a remarkable relationship with the PC1 of tree-growth (r=0.89). Our results suggest that SM is the main factor controlling the tree growth in multiple species in MC, and the current growth decline since the year 2007, is a response to the unusual SM decrease during the MD.