Second-Growth Forests Exhibit Higher Sensitivity to Dry and Wet Years than Long-Existing Ones: Second-Growth Forests Exhibit Higher Sensitivity: R. Balaguer-Romano and others.

Second-growth forest establishment over abandoned agricultural lands has been envisaged as a nature-based solution to reduce atmospheric CO2 through carbon sequestration. However, we still have a very limited knowledge about the climate sensitivity of these second-growth forests in comparison to forests with a more continuous land-use history. Here, we compare the climate sensitivity of recently established forests (post-1956) and long-existing forests (pre-1956), by analyzing their responses to climate variability at 456 inventory plots in NE Spain. We analyzed remotely sensed estimates of leaf area index (LAI) and normalized difference vegetation index (NDVI) from 2000 to 2022, relating yearly variation patterns with annual meteorological drought intensity. Then, we used process-based simulations of forest functioning to explore whether different responses of both forest types to climate variability are consistent with differences in root allocation patterns modulated by land-use legacies. Although recent- and long-existing forests had a very similar structure (that is, similar LAI), NDVI variation in recent-established forests was more strongly related to meteorological drought indices, recording steeper NDVI decreases during drier periods, but also higher NDVI increases during rainy years. This pattern is consistent with differences in root allocation between the two forest types, as simulated and remotely sensed forest responses to climate exhibited higher correlation when we inputted recent-established forest with shallower root systems or lower fine root density in comparison with long-existing forests. A higher climate sensitivity of second-growth forests during drier but also wetter years entails the potential for compensating drought impacts, but it also indicates a long-term higher vulnerability to climatic disturbances. [ABSTRACT FROM AUTHOR]