Basal area growth and mortality of Betula maximowicziana affected by crown dieback in a secondary forest in Hokkaido, northern Japan

Since the late 1990s, decline of B. maximowicziana Regel has been observed in mature secondary forests in various parts of Hokkaido, northern Japan. To develop a method of thinning for large-timber production of B. maximowicziana, we measured basal area growth and the mortality of 217 trees during a four-year period (1999-2003) in a 90-year-old secondary forest with serious tree damage. We analyzed growth and mortality in relation to the degree of crown dieback (DC), symmetric and asymmetric competition from neighbors, and initial tree size. Individual basal area growth decreased with increasing DC, with increasing symmetric (two-sided) competition, and with decreasing initial tree size. During the four-year period, 4.1% of the observed trees died. Logistic regression analysis revealed that mortality rate increased with increasing DC and with increasing symmetric competition. These results suggest that both growth and mortality rates were affected by the same factors (i.e., DC and symmetric competition). We concluded that the resource for which individuals were competing at the study site was underground, most likely water. Modeled growth and mortality rates can be used to improve the management of damaged forests. A management plan for the damaged study site is proposed.