Divergent climatic response patterns of radial growth in healthy and declining poplar forests in the Engebei Ecological Demonstration Zone of Ordos, China.

Introduction: Climate warming-induced extreme drought has led to substantial growth decline and extensive tree mortality in forests worldwide, with such phenomena being particularly pronounced in plantation ecosystems. This study aimed to assess the divergent climatic responses of radial growth between healthy and declining Simon poplar ( Methods: Separate ring-width chronologies were developed for healthy (1996-2024 period) and declining (1994-2024 period) Simon poplar plantations in the Engebei Ecological Demonstration Zone of Ordos, to explore their differing responses to climate factors. Results: All statistical parameters of the declining chronologies were higher than those of the healthy ones, indicating that the declining chronologies exhibited higher quality and stronger common signals, whereas the healthy chronologies were comparatively weaker. Climate-growth response analyses revealed that radial increments of declining trees displayed significantly greater sensitivity to climatic variability than healthy trees, while the basal area increment showed the opposite pattern-declining trees had markedly lower climatic sensitivity than healthy individuals. As Simon poplar trees enter the growth decline phase, drought stress exerts increasingly strong suppressive effects on radial growth, while the warming-induced stimulation of basal area increment becomes progressively weaker. Discussion: The divergent responses of radial growth and basal area increment to climate variability underscore the key climatic determinants shaping the decline of poplar plantations across the study area. Overall, this study contributes to a mechanistic understanding of climate-driven growth decline in poplar plantations of the Ordos area and provides a scientific basis for ecological restoration and sustainable management of local degraded plantations.