Contrasting climatic controls on bimodal growth of Pinus elliottii plantations between northern and southern subtropical zones

Abstract

Subtropical plantation forests play a crucial role in the global carbon cycle, yet intensifying global warming may exert profound impact on tree growth and forest carbon uptake. Pinus elliottii Engelm. is a widely planted and representative plantation species in subtropical regions, valued for its rapid growth and broad ecological adaptability. Despite this, the intra-annual growth dynamics of this species in response to heatwaves remain poorly understood. Specifically, it is unclear whether P. elliottii plantations exhibit divergent sensitivities between the northern subtropical region (NS) and southern subtropical region (SS), and which factors govern these responses. Here, we combined dendrochronology with the process-based Vaganov-Shashkin (VS) model to investigate radial growth dynamics of P. elliottii between the NS and SS under both background warming and heatwave events. Growth-climate analyses indicate that radial growth in SS is strongly constrained by high summer temperatures, whereas the climatic sensitivity in NS is comparatively weaker. Despite exhibiting similar bimodal growth patterns, VS-model simulations reveal fundamentally different underlying controls between NS and SS. In NS, growth is primarily regulated by soil moisture availability, while in SS is modulated by supra-optimal temperatures in summer. Therefore, such contrasting growth mechanism results asymmetry in heatwave vulnerability between the two regions. These divergent growth responses highlight the heightened vulnerability of SS plantations to intensifying heatwaves, emphasizing the urgent need for heat-resilient management strategies. More broadly, these findings suggest that the NS region serves as a potential climate refugium for P. elliottii under future warming scenarios, warranting a reassessment of its future climatic envelopes and ecological boundaries.