Examining Forest Structure and Growth Dynamics Using Dendrochronology

Extreme climate events pose a potential threat to the forest structure stability, triggering tree growth release (GR) and possible shifts in tree social status. This study used a dendrochronological approach to investigate changes in tree competition in a 100-year-old Japanese cedar (Cryptomeria japonica) plantation at the JinGangZuan site, managed by the Experimental Forest of National Taiwan University. Tree-ring data was used to reconstruct historical GR events and explored the relationship between GR and the maximum wind speed. In addition, we evaluated tree social status shifts by comparing each sample tree’s diameter at breast height (DBH) with the stand’s quadratic mean DBH from forest inventory data.

Our findings identified a major GR event around 1970 and revealed a significant positive correlation (r = 0.73, P = 0.01) between GR and maximum wind speed. Most high wind events occurred during typhoon periods. Despite these disturbances, the overall social structure remained largely unchanged among the 113 sampled trees, suggesting that GR does not necessarily drive significant status shifts. Specifically, 79.6% of trees retained their original social status (“big trees remain big and small trees remain small”), while 20.4% exhibited some degree of status change. Most codominant-to-dominant status changes occurred in early growth stages, while status change in later stages appear to be randomly distributed. We suspected disturbances tend to remove weaker trees, complicating direct comparisons among individuals.

Notably, typhoon strength has increased over the past four decades and is expected to intensify further under global warming. Although this study suggests minimal impacts of disturbances on forest structure at the JinGangZuan site, proactive adaptation measures are advisable. Tree-ring analysis offers valuable insights into stand development following extreme events, providing critical guidance for refining forest management strategies in an era of changing environmental conditions.