Structure and regeneration of a mixed evergreen broad-leaved stand and a pure stand of Persea thunbergii at its northern limit along the Pacific Ocean, Japan.

Abstract

We compared the stand structure and regenerative conditions of Persea thunbergii on a mixed and a pure P. thunbergii forest on two neighboring islands of northeastern Japan along the Pacific Ocean. The relative dominance of P. thunbergii at the basal area exceeded 0.9 in a pure stand on Tsubaki Island. The height distribution of trees was bimodal ; one peak was the upper layer occupied by P. thunbergii, and the other was the lower layer occupied by Camellia japonica. There were 662 (/ha) saplings (height≧1.3m and DBH<5cm) of P. thunbergii, 85% of which originated from sprouts. In a mixed stand on Yakei Island, three evergreen broad-leaved trees, P. thunbergii, Daphniphyllum macropodum and Ilex integra, were the major canopy species. The relative dominance of these three species at the basal area was 0.45 (P. thunbergii}, 0.19 (D. macropodum}, and 0.16 (I. integra}. The mixed stand had a continuous tree-height distribution. There were many saplings (1055/ha) of P. thunbergii, and most of which were raised from seeds. Significantly more light was available in the mixed stand than in the pure stand, although there was no difference in the gap rate between the two stands. This difference in the light environment may arise from the differences in stand stratification. Thus, the heterogeneity of stratification may promote recruitment into saplings in a mixed forest, in contrast to a pure forest.