Age and size distribution in a long-term forest dynamics

Abstract

To examine regenerational patterns in a long-term forest dynamics, age and size distribution was studied in an old-growth deciduous oak ( Quercus mongolica var. grosseserrata) forest in northern Hokkaido, Japan. The frequency distribution of size classes (diameter at breast height and tree height) showed continuous size structures with a large number of smaller trees and a small number of larger ones. The distribution of diameters showed a reversed-J shape, and that of heights had small peaks showing vertical strata. The frequency distribution of ages, on the other hand, showed discontinuous and periodic patterns with an interval of approximately 100 years between the peaks of age concentration. This period would be related to the stem exclusion and understory reinitiation stages in forest stand dynamics. Although the age distribution showed a discontinuous pattern, the relationship between ages and sizes was well fitted to logarithmic regressions. The curve fitting was better for diameter than for height, and the age distribution also demonstrated the existence of several cohorts in a stand. The cohorts ranged widely in size in the old-growth forest and demonstrated a gradual decrease in regeneration following the most concentrated period. These results suggest that the concentrated regenerations would be established several times in long-term forest development showing multicohort structure and cyclic forest dynamics. Forest management should be planned with the recognition of such results and decisions made concerning long-term forest dynamics.