Disturbance Regime and Herb Responses to Canopy Gaps in Mt. Jumbong in Central Korea
School of Life Sciences,The Catholic University of Korea, Korea
This study was carried out to determine the disturbance regime and the responses of herbaceous plants to canopy gaps in Mt. Jumbong, which lies within the core area of the Mt. Sorak Biosphere Reserve. In order to characterize the gaps occurring in Mt. Jumbong, all the canopy gaps within the 16 ha study site were visited, the size and age of gaps were estimated, and gap-makers and replacers were determined for each gap. The area of canopy gaps accounted for 0.64% of the forested area, and that of expanded gaps for 2.02%. About one third of the gaps were older than 10 years old, but half of the gaps were younger than 5 years old, indicating that many gaps in Mt. Jumbong are small and close relatively early. Most of the canopy gaps were less than 80 m2 in size, with the mean of 34 m2. These results indicate that the disturbance regime of Mt. Jumbong is dominated by small scale gaps formed mostly by the windthrow of one or two canopy trees.
Quercus mongolica was responsible for the formation of about 42% of the gaps, and Ulmus laciniota, which grows in the valleys, were the next frequent gap-maker. In contrast, Acer pseudosieboldianum, Acer mono and Acer tschonoskii filled about half of the gaps, but many other species were involved in the gap-filling. These results suggest an increase in species diversity and evenness of the tree layer and an increase in the proportion of shade-tolerant tree species in Mt. Jumbong in the near future.
Seasonal changes of herb responses and environmental factors to the presence of absence of gaps were investigated too from April to August, 1996 in Mt. Jumbong. Three experimental gaps were created by cutting subcanopy trees and saplings on the valley, north-facing slope (N-slope), and ridge. Forty 1 m2 quadrats were established from gap center to non-gap in each artificial gap. Light intensity and soil temperature were highest at the gap center and decreased toward non-gap at the valley and ridge in May prior to leaf development in the canopy, but the difference was not significant in the gap on north-facing slope. When the canopy leaves were fully developed in August, relative light intensity and soil temperature were highest at the gap center and decreased toward non-gap at the valley, N-slope and ridge. Except for on the ridge, soil moisture content was not significant along the distance from gap center to non-gap.
Herb responses to gaps were investigated at the population level and at the community level. At the population level, dominant species of all the sites, Erythronium japonicum and Symplocarpus nipponicus, were examined for density, coverage, and reproduction rate. Emergence rate and diameter of S. nipponicus in April were higher in gaps than in non-gaps. Seed production rate of E. japonicum and S. nipponicus was highest at the gap center and decreased toward non-gap. At the community level, total biomass on the valley, N-slope and ridge were higher in gaps than in non-gaps. On the valley, species diversity and evenness were higher in non-gaps than in gaps. On the contrary, species diversity and evenness were higher in gaps than in non-gaps on the N-slope and ridge. In conclusion, environmental gradients created by gap formation affected life history traits such as emergence rate and reproduction rate in some species like E. japonicum and S. nipponicus, and it was suggested that as niche specialization occurs in old gaps, some species might have adapted themselves to gap-phase, and thus disturbance can increase species diversity of the herb community in deciduous hardwood forests.
Key Words: Canopy gaps, Deciduous hardwood forest, Disturbance, Herbaceous species, Light intensity, Succession