What are reasons for the failure of natural regeneration of Pinus densiflora for the last decade in Mt. Gariwang, Central East of Korea?

Background/Question/Methods Korean red pine (Pinus densiflora Siebold & Zucc.) is one of the most commonly found and historically beloved species in Korea. Since it is one of the pioneer species in the region, a seed-tree cutting method has been implemented to succeed red pine forest. However, the forest has not been well-regenerated after the seed-tree cutting since 1998, ca. 10ha, in Mt. Gariwang. In the previous study, animal feeding, high soil moisture, and competition of light with other vegetation have been suggested as the critical limiting factors for the failure of the regeneration, but were not verified. We applied randomized complete split-split-plot design to clarify these factors: drainage treatment for main plot, fencing for sub-plot, and weeding frequency for sub-sub-plot. We sowed 2,240 seeds in May 2013 and observed the germination rate, survival rate, and height and root collar diameter growth. Temperature and relative humidity in the air, precipitation, soil water contents and soil temperature were monitored.

Results/Conclusions Most of seeds (64%) were germinated in June 2013. At the first year, the mortality of seedlings was twice higher at the no weeding than treated plots (p=0.05). However, the mortality of seedlings with twice and three times of weeding was doubled than that of no weeding (p<0.05) in the second year. During winter of the third year, most of seedlings’ terminal bud was significantly damaged by animals. The height of seedlings grown in none weeding site was shorter than that in weeding treatment (p<0.05). However, root collar diameter increased as weeding frequency increased (p<0.01). Unexpectedly, seedlings’ survival rate and growth were not affected by the soil water contents even though these were significantly different between treatments. We observed that frequent weeding in the first year may intensify drought stress on seedlings and fencing was only effective to prevent large-sized mammals’ interruption, but work as a shelter for rodents. This study suggested that the critical factors for P. densiflora regeneration at the early stage were varied according to the seedlings’ development stage.