The effect of forest-thinning works on tree growth and forest environment

摘要

This research was conducted to provide effective forest management through forest tree production and forest land changes which took place after the forest-tending works in the plantation of Pinus koraiensis . It has been shown that the current annual diameter growth of trees in regions which implemented forest-tending projects in 2005 had increased by 142.9% compared to those which did not implement the forest-tending projects. In 2006, the current annual diameter growth of trees in implemented regions increased by 132.6% compared to those which did not implement forest-tending. Additionally, in the Pinus koraiensis plantation of Ⅲ·Ⅳ age classes where forest-tending projects works were implemented, the growth in diameter started to show a clear increase in the year following the implementation, and the maximum effects were displayed within 3–5?years. Thereafter, the growth gradually started to slow down. Therefore, implementing forest-tending works repetitively with a minimum period of 5?years would be considered appropriate. Soil moisture during the rainy season did not show significant differences as the soil moisture content remained at 40.4–43.0%. However, during the dry season, regions which did not implement forest-tending showed an average of 20.4%, and regions which implemented forest-tending showed an average of 26.6%, and the differences were greater when compared to the rainy season. Due to the control in the density of the number of forest trees due to forest-tending and forest thinning works, the number of understory woody plant species increased from 17 to 30 and the number of herbaceous plant species increased from 20to 44. Furthermore, as the density of standing trees was reduced to about 50% in places where forest-tending works were implemented, crown length ratios increased greatly from 46.1% to 62.1% and became a great help to the growth of forest trees.