Regeneration in subalpine coniferous forests

Death of canopy trees when gaps are formed was studied in a subalpine coniferous forest, central Japan, which was composed ofAbies, Tsuga, Picea, Betula, andSorbus. Typhoons were considered to be the most important cause of the death of canopy trees. The degree of disturbance in each of 16 plots (20 m×20 m) was represented by the percentage of the total basal area of dead trees to that of living and dead canopy trees (disturbance magnitude; MAG). The mortality of canopy trees increased as their dbh increase in the plots of lower MAG than 90%. The mortality varied among genera, andTsuga was characterized as having lower mortality than that of the other conifers. 418 dead trees were observed. The standing dead trees made up 10.7% of the trees, the stem broken trees 46.7%, and the uprooted trees 42.2%. The stem breaking was most frequent inAbies, and the uprooting was most frequent inTsuga, Picea, andBetula. Undeveloped forests, which have the L-shaped dbh distribution, were destroyed only in high degree (70%<MAG), while developed forests were destroyed in various degrees (30%<MAG<100%). The percentage of uprooted trees in basal area decreased with the development of the forest, from 60% to 10%.