Verification of effective timing of repellent application to browsing by sika deer on hardwood seedlings

Effective schedules of the application of repellent to minimizing browsing by sika deer (Cervus nippon yesoensis) on hard wood seedlings in relation to the shoot growth phenology were proposed (Akashi et al. 2012b). This study verified the schedules in the plantations of Fraxinus mandschurica, Ulmus davidiana var. japonica, and Quercus crispula in Shibetsu, Hokkaido. The effect of the repellent application in autumn was examined in the next spring. Five treatments (twice applications according to the schedules proposed by Akashi et al. (2012b), single application at high-priority time, single application at low-priority time, no repellent application, and three times applications) were configured. The effect of the repellent application in autumn was not clear because there was little browsing in winter. Browsing intensity on tree seedlings from spring to autumn in 2012 was extremely higher than in 2011, and the effect of the repellent application on tree growth was weak. U. davidiana was the highest tree height on July 31, and then decreased in height on October 9 by heavy browsing. However, the repellent application on August 2 was effective for enhancing height growth. Browsing on F. mandschurica was slight on June 20, and then it increased. The repellent application on July 31 was effective for browsing on F. mandschurica. Repellent application reduced browsing only immediately after application. From these results and the previous report (Akashi et al. 2012b), we recommend the following application schedules for applying a repellent twice annually: U. davidiana, in June and in late July/early August for protecting growing shoots; F. mandschurica, in late June when the growth of the current-year shoots is completed, and in May when just after planting or in late July/early August depending on the timing of regional heavy browsing. ; and Q. crispula, in May and in late July/early August. Because all tree species are browsed more severely as the seedling height increase, repellent application three times annually may be insufficient to protect their shoots in the area where extremely heavy browsing occurs.