Legacy effects of past thinnings modulate drought stress reactions at present

ABSTRACT Thinning experiments were primarily established for analysing how treatment variants determine the amount and quality of wood production. Given climate change, they may also explain how silvicultural treatment determined drought resistance. Especially for tree species cultivated in regions beyond their natural range, silvicultural treatment may help mitigate drought stress. Here, we used the 47-years-old combined spacing-thinning trial Fürstenfeldbruck 612 and metrics for quantifying the trees’ recent and past growth to test if the information of tree treatment and development in the past significantly improved the prediction of their growth at present and if spacing and density regulation, kind of thinning, and temporal sequence of thinning significantly co-determined tree and stand growth during drought. Based on linear models, we revealed the following ecological legacy effects: (i) information of tree treatment and development in the past significantly improved the prediction of their growth at present, and (ii) higher densities, past thinnings from below, and low variations in thinning strength were beneficial for the tree and stand growth during drought. Thus, the prevailing repeated strong thinnings from above for promoting a selected collective of future crop trees may be questioned because of climate change.