Partial crown mortality as a proxy of Nothofagus dombeyi’ growth performance: post‑drought growth responses and legacies

Abstract

Globally, more frequent and severe droughts are driving increased tree crown defoliation, loss of vigor, and tree mortality, having detrimental effects on forest structure and functioning. This is the case of N. dombeyi, a broadleaf evergreen species, that has strongly suffered from negative drought-induced impacts during the last century. Here we analyzed differences in long-term growth trends, post-drought and post-wetness responses, drought legacies, and early warning signals of co-occurring healthy, apparently non-healthy (partial crown mortality), and dead N. dombeyi trees growing in northern Patagonia. Trees experienced growth reductions under selected droughts but recovered their pre-drought growth level when the drought ended. Trees with partial crown mortality levels exceeding 50%, and dead trees, exhibited significant growth decline. Growth decline was associated with reduced growth and a negative long-term post-drought response. This highlighted an irreversible decrease towards the more recent droughts, indicating a state change which denotes a negative legacy effect. The occurrence of successive dry and wet years during the last decades shaped the growth trend of healthy N. dombeyi trees, but resulted less informative for trees with higher crown mortality levels. Similarly, regular early warning metrics did not emerge as strong predictors of vigor loss. The study sheds light on the multifaceted factors influencing crown dieback dynamics, and underscores the need for further research on tree health and resilience.