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We measured photosynthetically active radiation (PAR) beneath the forest canopy, understory species' richness and diversity, and biomass in a Larix leptolepis plantation in central Korea 4 years after thinning. Four different thinning intensities (control, 10%, 20%, and 40% stocking reduction) were applied in 1997. Mean annual intercepted PAR at 30 cm and 1 m above ground level was significantly different among the thinning intensities and strongly correlated with the number of stems remaining after thinning. Understory species richness and diversity were lowest in the unthinned stands and increased with thinning intensity, and there were significant correlations between the total number of understory species or diversity index (Shannon's diversity index, HЈ) and the number of stems per hectare after thinning. Also understory above-ground biomass was significantly increased with thinning intensity in both sampling months (June and August 2001). Thinning increased light inputs to the ground and resulted in higher species richness and diversity and above-ground biomass. These results suggested that light availability and understory responses to thinning at a comparable intensity are likely to last well beyond the 4 years of this study.

Changes in land use can affect the distribution and cycling of soil organic matter and nutrients. Soil organic carbon (C) and nitrogen (N) concentrations, soil CO 2 evolution, litter decomposition, and soil N availability under the three types of conversion of agricultural lands to natural vegetation (rice field conversion to forest, crop field conversion to shrub, and indigenous forest) in central Korea after 20 years of fallow were compared. There was no significant change in soil organic C and N concentrations among the three types at the three soil depths, and soil organic C and N increases were confined to the topsoil (0 -10 cm). Soil CO 2 evolution tracked seasonal soil temperature, however, there was no difference among conversion types. Annual soil CO 2 evolution (Mg CO 2 /ha/yr) was 36:0^3:7 for the rice field conversion to forest site, 33:8^4:1 for the crop field conversion to shrub site, and 40:7^4:1 for the indigenous forest site, respectively. After decomposing for one year, 55.8% for the rice field conversion site, 64.9% for the crop field conversion site, and 66.3% for the indigenous forest site of the original leaf litter mass remained. The soil moisture condition seemed to limit the rate of decomposition in the study area. Resin NO 2 3 -N concentration was higher at the rice field conversion site.

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