Post-Tsunami Forest Resilience in a Coastal Forest Ecosystem After the Mega-Tsunami of 2011, Japan

Coastal protection forests in northeastern Japan were strongly affected by the 2011 Great East Japan Earthquake and tsunami. We assessed the post-tsunami response of a Japanese black pine (Pinus thunbergii) stand in the Ishinomaki coastal forest to identify growth suppression and post-disturbance recovery patterns in surviving trees. Dendrochronological data from 30 trees covering 2006-2020 were used to evaluate radial growth through standardized tree-ring indices, basal area increment, classical resilience indices, and additional recovery metrics. Annual stable carbon isotope discrimination (Δ¹³C) and intrinsic water-use efficiency were also examined in four cross-dated trees. The tsunami induced a clear reduction in radial growth during the first years following disturbance, with minimum growth occurring early in the post-tsunami period. This decline was accompanied by reduced Δ¹³C and increased intrinsic water-use efficiency, suggesting a short-term physiological response associated with restricted water uptake and salinity-related root-zone stress. Post-disturbance trajectories varied markedly among individuals. Some trees rebounded rapidly, whereas others showed delayed recovery and persistent growth suppression for several years. Based on recovery duration, trees were classified into early, intermediate, and late recovery groups, demonstrating greater individual variability than indicated by the stand-level mean chronology. Most surviving trees eventually returned to or exceeded pre-disturbance growth levels, indicating considerable resilience. However, rebound timing differed substantially among individuals. Spatial analysis revealed no significant clustering of recovery duration, suggesting that tree-level characteristics or fine-scale microsite conditions, rather than simple spatial patterns, influenced post-tsunami dynamics. Combined tree-ring and carbon isotope indicators further showed that physiological adjustment preceded full radial growth recovery. These findings highlight the value of integrating dendrochronological and isotope-based indicators to evaluate delayed physiological stress and long-term resilience following extreme coastal disturbance.