The purpose of this study is to suggest proper regulation period for three different silvicultural systems (selection forest, two-storied forest, and shelter-wood forest) based on structural diversity, species diversity, and competition characteristics of the stands in a natural deciduous forest in the north temperate region of Korea. Based on the current stand conditions, equations were developed to predict diameter growth rate, distribution of young growth reproduction, and height growth curve for the next 30 years at 5-year interval. These predictions were then used to derive the proper interval for silvicultural applications to reach the target stand conditions. The predicted stands at each of the 5-year-interval were represented by 8 stand structure indices, 6 species diversity indices and one competition index, and their usefulness were evaluated.
Our results suggest that additional prescriptions were necessary at year 10 and 20 to ensure proper stand density and to reach target stand conditions for all silvicultural systems. For each additional prescription, it was determined that removal of 13-27% of basal area is required to maintain the stand density for optimal growth. Under such prescription schedule, regulation period could be reached after 30 years for all silvicultural systems considered.
For the selection forest, sustainable timber production could be acquired after 30 years. The differences between the target and predicted stand characteristics were minimal. For the two-storied forest, the resulting stand showed distinct over- and under-story structure, and sustainable timber production was possible from harvesting over-story trees. The shelter-wood forest also showed sustainable timber production.
Four of the eight structural indices, e.g., Contagion index, DBH-Difference, Height-Difference and Mingling index, were useful for quantifying and comparing the spatial structure of the changing stand conditions over time. In all silvicultural systems, we predicted that Contagion index will immediately decrease after the prescription events but will continuously increase in between them. When compared with the current condition, Contagion index only slightly decreased after 30 years. This suggests that the stands may exhibit a more regular spatial pattern to some extent. However, the change may be too small (range of 0.30-0.35) to indicate a significant deviance from the current natural stand structure. Both DBH-Difference and Height-Different were predicted to increase after 30 years (ranges of 0.40-0.45 and 0.30-0.35, respectively), indicating that the resulting stands will show greater horizontal and vertical structural diversity, and will resemble the structural aspects of the current natural stands. Mingling index showed mixed results: it increased in the selection system but remained constant in the other systems.
Shannon’s diversity index, Pielou’s evenness index, and number of tree species were determined to be useful for evaluating and comparing changes in species composition over time. Shannon’s diversity index only slightly increased in the selection system and remained constant in the other systems, indicating that a significant change in species composition is not likely to occur. Pielou’s evenness index showed a fluctuating pattern over time, ending with a slightly lower value after 30 years compared to present condition. However, the overall change was too small to indicate any meaningful change in tree species diversity. Number of tree species also did not show any meaningful changes over time.
For all silvicultural systems, Hegyi’s competition index was lower immediately after each of the prescription events. After 30 years, however, it showed a slight increase in the selection system but remained constant in the other two systems.
Our results suggest that all silvicultural systems considered will be able to produce timber at a sustainable level at the end of the regulation period. At the same time, they were able to maintain the current stand structure, species diversity, and competition level that are characteristic of natural stands. We conclude that selection forest, two-storied forest, and shelter-wood forest can all be considered as environmentally-friendly silvicultural systems, and can successfully improve the economic and ecological values of the future forests.