The recent rapid increase in the demand for tree lacquer from Toxicodendron vernicifluum for national treasure has made it essential to cultivate T. vernicifluum forests and increase the production of its seedlings. The seeds of T. vernicifluum are dormant and have a low germination rate. Moreover, their germination rates vary even after dormancy-breaking treatments. The presence of empty seeds may be one possible cause, which can be tackled via specific gravity sorting with salt water. However, increasing the specific gravity of the solute may improve the selection rate. In this study, sucrose was used as a solute to improve the sorting rate in the specific gravity sorting of T. vernicifluum seeds. The results showed that the sedimentation rate decreased even at sucrose concentrations exceeding a saturated salt solution. This finding suggests that even non-sufficient seeds, which cannot be removed by saltwater sorting, could be removed using this method. Furthermore, the germination rate of the selected T. vernicifluum seeds increased with increased sucrose concentration. Increased germination rates were also observed in seeds settled in sucrose solutions with a specific gravity higher than that of saturated salt solutions, suggesting that the settled seeds in saturated brine were empty.

To investigate the effect of retention forestry on nitrate concentrations in stream water in the Todo-fir plantation, aged 50 years or more and at the main harvest stage, we conducted a harvesting experiment in a small watershed with an area of about 10 ha at the foot of Irumukeppu volcano in the Sorachi district of Hokkaido. We compared the changes in nitrate concentrations in the watershed during the 10 years before and after harvesting (2 to 3 years before and 7 to 8 years after harvesting). In watersheds where 45-50％ of the trees were retained, there was almost no increase in nitrate concentrations, and in watersheds where 20-30％ of the trees were retained, it increased for 3 years after harvesting. In several watersheds where retention forestry was conducted, nitrate concentrations were lower than before harvesting from the fifth year after harvesting, suggesting that growth recovery of retained trees and understory vegetation were suppressing nitrogen runoff.

There is a growing awareness of retention forestry, a silvicultural system that retains important forest structures at clearcutting, to conserve forest biodiversity. We investigated the effects of retention of broad-leaved trees on bird diversity in cypress and cedar plantations, Kochi, southeastern Japan. In June and October 2023, we surveyed birds in a retention site and an adjacent clearcut area as reference site using IC recorders. We compared avian species richness and Simpson diversity index between retention and clearcut areas. As a result, tree retention did not significantly affect avian species richness and Simpson index. But we found a significant interaction effect between tree retention and survey season on avian species richness and Simpson index, suggesting that the positive effect of retention on species richness was stronger in October than in June. We highlight that retention forestry would be beneficial for bird conservation even in cypress and cedar plantations.