Importance of pre-release height of saplings in governing mortality factors after canopy opening: insights from 21-year monitoring of Abies sachalinensis saplings

Abstract

ABSTRACT This study examines the impact of canopy openings on the regeneration of naturally regenerated pre-released saplings of Abies sachalinensis, an evergreen conifer. The investigation spans 21 years, aiming to understand the influence of canopy opening on sapling mortality and growth dynamics. The research records the height and mortality of over 1100 individuals while maintaining individual identification throughout the study. By delving into the long-term effects, this study provides valuable insights into how canopy openings shape sapling dynamics over time. Observations revealed a significant increase in the annual mortality rate of saplings during the year of canopy opening, which persisted for three years. Following this, all saplings survived for the subsequent two years. The post-release mortality rates indicated an inverse correlation with the sapling height of the preceding measurement. The impact exhibited an increasing trend over the years, reaching its peak; however, the decline commenced 14 years post-release. Pre-release height rank notably influenced subsequent sapling height, though this relationship was notably less stable during the first seven years post-release. Furthermore, the growth rate exhibited a pre-release height-dependence, growing stronger each year. Nonetheless, during the 3–4 years after canopy opening, this height-dependence diminished compared to pre-release levels. This research underscores the significance of long-term monitoring in unraveling the complex relationships between canopy opening, sapling mortality, and growth dynamics. By investigating these processes over two decades, the study provides valuable insights into forest regeneration and gap dynamics, shedding light on how various factors interact to shape tree population dynamics.