The Impacts of a Large Hurricane on Understory Sapling Dynamics and Diversity in North Carolina Piedmont Forests, USA

摘要

We analyzed population dynamics and changes in species diversity and composition of saplings (tree or shrub stems >50 cm in height and < 1 cm diameter at breast height) during an interval lasting from 5 years before the 1996 Hurricane Fran to 5 yearspost-hurricane through use of permanent transects where individual sapling stems were censused annually. The study site was the Duke Forest, located in the Piedmont plateau, North Carolina, USA. We hypothesized that understory sapling dynamics are significantly influenced by canopy tree damage caused by the large, infrequent hurricanes, through enhanced recruitment of light-demanding species and increased growth rates of established saplings. Our results showed that sapling damage by Hurricane Fran waslargely secondary (i.e. 44-70% of damaged saplings were pinned to the ground by falling parts of large neighbor trees). All survey transects experienced decreased sapling density as a result of increased mortality. The average mortality rate of saplingsnearly doubled, increasing from 7.04 ± 3.98% to 13.22 ± 5.71%. Although the changes in sapling density were dramatic, species diversity of saplings remained relatively stable or decreased slightly due to the hurricane-induced damage. Large gaps createdby the hurricane resulted in the release of established, shade-intolerant or mid-tolerant saplings. We conclude that large, infrequent windstorms appear to be responsible for temporal and spatial variation in understory regeneration.