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

The Mega-Tsunami of March 2011 in eastern Japan caused severe damage in the coastal black pine (Pinus thunbergii) forests along the Pacific coast. To evaluate post-disturbance forest recovery, tree-ring samples from 30 trees at Ishinomaki coastal forest were analyzed for the period 2006–2020 using tree-ring indices and stable carbon isotope discrimination (Δ13C). The results revealed a strong decline in radial growth immediately after the tsunami, indicating severe growth suppression during the years 2011–2014. Simultaneously, Δ13C values decreased, suggesting reduced stomatal conductance and acute physiological stress associated with the initial salinity effect at the root zone. Although isotopic signals indicated gradual physiological adjustment in subsequent years, radial growth recovery occurred more slowly. Most trees returned to pre-disturbance growth levels within approximately 3–5 years and later exceeded pre-disturbance growth levels, likely due to reduced competition following the mortality of nearly 40% of trees after the tsunami. However, recovery trajectories differed markedly among individual trees, with some trees showing prolonged growth suppression beyond 6 years. This variability may reflect highly localized or tree-level factors, including intrinsic differences in individual resilience, while spatial autocorrelation analysis did not indicate significant clustering of recovery time across the stand. We conclude that black pine coastal forests show a high degree of resilience, showing physiological recovery in a short period (3–4 years). Although growth recovery took longer, initial tree mortality promoted the growth of the surviving trees beyond pre-disturbance values.