Diurnal and Seasonal Fluctuations in Stem Diameter of Young Pinus densiflora and Chamaecyparis obtusa Trees

アカマツ2個体，ヒノキ1個体につき，各1か所の幹直径の変動を，ひずみ計利用の生長計によって，1977年5月から1978年8月までの16か月間にわたり計測した。幹直径は早朝の5時～8時に最大，昼すぎの13時～16時に最小のことが多い。幹直径の日変化の幅は，日射量の多い晴天の日が曇天や雨天より大きく，また生長のさかんな季節が冬よりも大きい。冬の最低気温が－4.0℃～－9.0℃にさがるような寒い早朝には，幹に寒冷収縮のおこることがある。肥大生長による幹直径の増加は，春なかばから秋なかばまで続く。アカマツ試料木では冬に，ゆるやかな幹直径の減少がみとめられた。Diurnal fluctuations in the stem diameter of the two Pinus densiflora trees and the one Chamaecyparis obtusa tree were recorded with an electric strain gauge dendrograph for a 16-month period May, 1977 to August, 1978. The maximum stem diameter was found at a time from 5 a.m. to 8 a.m. and the minimum one from 1 p.m. to 4 p.m. in each day usually. The diurnal fluctuations in stem diameter were remarkable on clear days in the growing season. In the early morning of the winter, a shrinkage of stem diameter occurred frequently when the minimum air temperature fell below -4℃. An increase in stem diameter probably caused by cambial growth was observed from late April or early May to mid October or early November. In Pinus densiflora trees, a gradual decrease in stem diameter continued throughout the winter