Effect of density control on tree growth at ecological tree planting sites in Japan

Abstract

The effect of density control of tree growth on revegetation sites planted by the ecological tree planting (ETP) method, one of the most common woodland creation methods devised in the 1970s in Japan, is analyzed. The ETP method is performed with the expectation of natural establishment of woodlands by planting saplings of native tree species composing potential natural vegetation in high density. The results show that the general growth condition of such woodlands is not inferior. Often, however, it is suggested that transition of the composition of the woodlands does not progress exactly along the transition expected, because of the characteristics of ETP sites, that is, even-aged forest despite the planting concept consisting of several tree species. Occasionally, expected natural selection does not occur. In such circumstances this is interpreted as suggesting that artificial density control, for example thinning, is necessary. A thinning trial was conducted on the ETP woodland in Himeji, Hyogo, Japan during the fourth year after planting, and tree growth was investigated in the third, seventh, and ninth years after thinning. The results show thinning has the potentiality to bring about substantial change in the establishment of multiple layered woodlands. When natural selection cannot be expected on ETP woodland, application of thinning as part of the management plan is important to establish ecological woodland with much ecological function.