A stand structure dominated by Betula maximowicziana in the Chichibu Mountains, central Japan

Summary In order to investigate the floristic composition and structure of a stand dominated by Betula maximowizciana, a research plot with an area of 0.96 ha was established at an altitude of 1,300 m a.s.1. in the Chichibu Mountains, central Japan. Diameter at breast height, (dbh) and the height of all the trees with dbh larger than 5.0 cm were measured in the plot. Thirty-nine tree species were recorded in the plot. The number of trees, basal area and stand volume were 1,177/ha, 42.0 square m/ha and 330.0 m sup 3/ha, respectively. For B, maximowicziana, these values were 83/ha (7.1%), 15.8 square m/ha (37.5%) and 154.7 m sub 3/ha (46.9%), respectively. The stand was stratified into three layers, the first-1ayer (height of layer: hl > 22 m) in which the predominant species was B. maximowicziana, the second-1ayer (14 < hl =<22 m) in which B. grossa, Quercus crispula and Carpinus tschonoskii were abundant and the third-layer (4< hl =< 14 m) in which Acer spp. Carpinus spp., Fraxinus languinosa and Clethra barvinervis were abundant. From the age analysis of twenty dead trees sampled within the plot and its surroundings, tree ages were in the range of 83 to 120 years. From the age analysis of five sample trees, which seemed to die recently, it was estimated that this stand was regenerated about 120 years ago. Numerical values of the stand in Chichibu plot were compared to those of the stands dominated by B. maximowicziana in two plots (plot no. 5133 and 5236) in the Tokyo Univ. Forest in Hokkaido, northern Japan. They were regenerated after forest fire and the stand age of plot no. 5133 and 5236 were 9 1 and 86 years, respectively. Qualitative thinning has been conducted three times in the former plot but this was not the case in the latter. Tree density and mean annual diameter growth rate of the Chichibu plot were similar to those of plot no. 5133. On the other hand, mean dbh and stand volume at the Chichibu plot was larger than those of the two plots in Hokkaido. However, from the viewpoint of the commercial value of wood utilization, the morphological characteristics of the B. maximowizciana trees in the Chichibu plot are inferior to those of the trees in plot no. 5133 where qualitative thinning has been conducted. Hence, for the production of high-quality large diameter trees, qualitative thinning should also be conducted especially to B. maximowicziana stands with an age less than 100 years. These are abundant in the Tokyo Univ. Forest in Chichibu. It is thought that the B. maximowicziana trees composing the canopy layer in the Chichibu plot at present are gradually being replaced by Quercus crispula in the long course of succession, since the latter, characterized by its longer life span and higher shade tolerance, has an advantage over the former.