No abstract

Scarification is widely conducted in northern Japan to remove understory dwarf bamboo species in degraded forests for replacement with tree species. To explore ways to enhance species diversity and restoration of mixed forest at the treated site, we clarified the mechanisms that lead to compositional heterogeneity of plant species. We evaluated the relative importance of environmental factors (scarification properties, soil properties, light conditions, litter cover, and presence of canopy trees) for the demography of tall tree species (emergence, mortality, and growth) and whole vegetation structure (species diversity and composition) over the two growing seasons immediately following scarification. Of tall tree species, Betula spp. were dominant (60% in total density), followed by Abies sachalinensis (Fr. Schm.) Masters, Acer mono Maxim., and Phellodendron amurense Rupr. Light intensity was an important factor, having mostly negative effects on the demography of these species. Soil factors (e.g., nitrogen content, moisture) affected the demography mainly of shade-intolerant or hygrophilous species. In general, extreme environmental conditions led to the dominance of grasses, forbs, and lianas rather than tall trees. Maintenance of canopy cover, which limits light and supplies seeds as well as litter, proved to be most important in promoting plant species diversification on the scarification site.

This data paper reports tree census data collected in a network of 34 forest sites in Japan. This is the largest forest data set freely available in Japan to date. The network is a part of the Monitoring Sites 1000 Project launched by the Ministry of the Environment, Japan. It covers subarctic to subtropical climate zones and the four major forest types in Japan. Forty-two permanent plots, usually 1 ha in size, were established in old-growth or secondary natural forests. Censuses of woody species ‡15 cm girth at breast height were conducted every year or once during 2004 to 2009. The data provide species abundance, survivorship and stem girth growth of 52,534 individuals of 334 tree and liana species. The censuses adopted common census protocol, which provide good opportunities for meta-analyses and comparative studies among forests. The data have been used for ecological studies as well as for the biodiversity reports published by the Ministry of the Environment.

Single tree selection has been employed widely in northern Japanese mixed forests, but management-induced changes in forests are not been well understood. This study examined demographic parameters of major tree species during 20-years in a 68-ha study stand, in which single tree selection has been conducted since 1971. Results showed that conifers (mostly Abies sachalinensis) gained the strongest positive effects from the treatment on growth and survival.Nevertheless, recruitment of conifers was not sufficiently improved, suggesting their decreased dominance over a longer-term. Instead, shade-intolerant broadleaved (mainly Betula ermanii) will gradually increase because of their higher recruitment rates after the treatment. Shade-tolerant broadleaved (mainly Acer mono and Tilia japonica) appeared to experience the most distinct negative effects, especially on survival. These trends differed markedly from those reported in previous papers concerning partial harvesting system, which predicted increase of shade-tolerant species. The results shown here should be generalized carefully because we have investigated only one stand without repetition of the control area. Nevertheless, trends described in this large-scale and long-term study could provide a basis for simulating stand dynamics. We discussed possible reasons for the observed patterns, and provided implications for sustainable management in the region.

Factors influencing the distribution of two co-occurring dwarf bamboo species (Sasa kurilensis and S. senanensis) in a conifer-broadleaved mixed stand in northern Hokkaido Abstract We have investigated the factors influencing the distribution of co-occurring two dwarf bamboo species, Sasa kurilensis (Ruprecht) Makino et Shibata and S. senanensis (Franchet et Savatier) Rehder, within a conifer-broadleaved mixed stand managed with selection cutting in northern Japan. We first sought the possible determinant factors (physical environment and overstory conditions based on 30 years' tree census data) deciding the dominant species in the plots (168 3.14m 2 area). We then examined the effects of these factors on the culm density and height of the dominant species. Linear discriminant analysis indicated that physical environmental conditions are important in determining the distribution; S. kurilensis tended to dominate plots with steep slope, convex shape and deep snow in early spring. Multiple regression analyses showed that culm density and height decreased significantly on steep slopes for both species. Also, the sum of the basal area (BA) of surrounding conifers (7.5 m radius around the plot), as well as the change in BA over the previous 30 years, had a negative influence on the culm height of both species. A reduction in overstory trees, caused by natural or artificial canopy disturbances, would increase the dwarf bamboo biomass. The effects of physical environment and overstory conditions, working through the dominance of the two dwarf bamboo species, should be taken into account in understanding the dynamics of natural forests in this region.