Growth of young Melia azedarach trees in abandoned farmlands as planting sites in western Japan

Melia azedarach is a fast-growing broad-leaved deciduous species native to Japan, and in recent years it has been regarded as a promising silvicultural tree species. The objective of this study was to clarify the factors controlling the growth of the target species in the field. Thirty-three research sites were established in western Japan, where stem diameter at ground level (D0) and at 1.2 m in height (D) and tree height (H) were measured every year, to compare the annual growth rates of individual trees. The stand age ranged from 1 to 8 years at the end of 2021. The mortality rate of each study site in 3 years after planting was higher when the mean temperature in the coldest month, January, was low. When this temperature is below 0 °C, the rate is higher than approximately 0.3. Analysis using general linear mixed models revealed that fertilizer application and the type of planted area (abandoned farmland) positively affected the annual growth rates of D0, D and H (ΔD0, ΔD and ΔH, respectively). The presence of an animal barrier positively affected ΔD0 and ΔH. Temperature in August and precipitation between July and August had a positive and negative effect on ΔD, respectively, whereas temperature in June had positive effect on ΔH. These findings can help to promote efficient silviculture by identifying good planting sites and management plans. Abandoned farmland is considered to be a prospective planting site, compared with forest.