Analyzing annual rings to evaluate past growth of natural cryptomeria japonica trees in sado forest reserve, akita prefecture, Northeastern Japan

Abstract

We investigated past growth of trees within a natural stand of Cryptomeria japonica in Sado Forest Reserve, Akita Prefecture, northeastern Japan, relating to temporal changes in environmental conditions. We cut 43 disc sections through the trunks of wind fallen trees selected from 3 locations within the reserve (area: ca. 25 ha). The wood samples were taken at 30∼200 cm height above ground. Average disc diameter was 62 cm. Mean number of annual rings per discs was 235, from which we calculated the average date of emergence at AD 1705 (after applying a correction taking into account the estimated number of extra years in the trunk wood below the cutting height). In order to evaluate historical conditions that may have affected growth performance of trees (e.g., canopy condition), we developed a discriminant function composed of trunk diameter and growth rate, which was estimated from the diameters and growth rates of current trees (height > 130 cm, dbh < 30 cm) within the same stands. Using this discriminant function, saplings which emerged in the early 18 th century were estimated to experience good growing conditions that soon deteriorated. However, for most trees, growth rate improved at around AD 1790. Estimated dates derived from these calculations were not significantly different among locations within the forest reserve. We conclude that this stand experienced two large disturbances in the 18 th century within about 85 yr. The first enhanced emergence of new trees and the second lead to improved growth. The most likely disturbance at that period of human history was likely felling of trees.