Scarification with surface soil replacement can promote understory reinitiation as well as the growth of a secondary birch stand

Abstract

ABSTRACT Soil scarification using heavy machinery has been widely used in the assisted natural regeneration of stands with a dense dwarf-bamboo understory in northern Japan. After scarification, birch forests have a high probability of growing, but dwarf-bamboos also recolonize the understory, resulting in the development of single-layered stands with lower levels of transition to the late-successional stage. In this study, we examined the long-term effects of an improved soil scarification practice called “replacement treatment,” in which the removed surface soil is returned to the scarified area. A previous study showed that the replacement treatment had a positive effect on the initial establishment and growth of birches. The site was remeasured at approximately 20 years of age, and the replaced stand, when compared with the standard scarification stand, had DBH and height values that were 1.5 times greater and stand volume that was 3 times greater. The difference in terms of height growth between the two stands widened especially during the first ten years. Additionally, in the replacement treatment stand the number of initiated saplings had more than doubled (> 100 thousand stems/ ha) and consisted of a diverse range of tree species. We have concluded that the soil replacement treatment is a suitable alternative practice that (1) significantly promotes the growth of birches and (2) promotes the reinitiation of tall-tree species in the understory and the development of the later successional stage.