報告書番号

481006

タイトル（和文）

植林地内伐開と隣接の樹木生長との関係－北西斜面における樹令２３年・スギ・ヒノキ混交林の場合－

タイトル（英文）

THE GROWTH OF TREES ADJACENT TO THE CLEARED AREA UNDER A TRANSMISSION LINE -CASE OF A PLANTATION OF MIXED 23-YEAR-OLD JAPANESE CEDAR WITH CYPRESS ON A NORTHWEST SLOPE-

概要 （図表や脚注は「報告書全文」に掲載しております）

植林地内に道路，鉄塔，送電線を設置するため林内の一部を伐開することにより生じた空間が隣接樹木の生長に及ぼす影響を定量的に知るため，山口県美東町において，北西斜面を横切る巾１０ｍの伐開地周辺のスギ，ヒノキ混交林（樹令２３年）を対象に調査した。伐開地は植林時にすでに存在していた。樹木密度は１５０平方ｍ当り３０～４５本（ｈａ換算２０００～３０００本），スギが５０～８０％を占めるヒノキとの混交林であった。林内の温・湿度，日射透過率が伐開により影響をうける範囲は伐開地から１０～１５ｍ林内に入った所までであった。伐開隣接地１５０平方ｍ当りの樹木現存量（スギとヒノキ合計）は材積が３．３～３．５立方ｍ，胸高断面積合計が０．６３～０．７３平方ｍであった。これらの値は伐開のない所とほぼ同じで，伐開による影響がないことを示していた。

概要 （英文）

IN ORDER TO CLARIFY THE EFFECT OF CUTTING OVER ON THE GROWTH OF TREES,STUDY WAS CARRIED OUT TO COMPARE THE GROWTH OF TREES ADJACENT TO A CLEARED AREA WITH THAT IN THE PLANTATION.THE CLEARED BELT WAS 10M WIDE UNDER THE TRANSMISSION LINE CROSSING THE NORTHWEST SLOPE OF THE MOUNTAIN(543M ALTITUDE) AT MITOO-CHOO,YAMAGUCHI PREFECTURE IN WESTERN JAPAN AND WAS MADE BEFORE THE ADJACENT TREES WERE PLANTED.THE PLANTATION IS MIXED 23-YEAR-OLD JAPANESE CEDAR(CRYPTOMERIA JAPONICA) WITH CYPRESS(CHAMAECYPARIS OBTUSA).THE TREE DENSITY IN THE PLANTATION FLUCTUATED IN THE RANGE OF 30 TO 45/150 SQUARE M(2000 TO 3000/HA). 1)COMPARING THE METEOROLOGICAL CONDITIONIN THE PLANTATION WITH THAT IN THE CLEARED AREA,TEMPERATURE IN THE PLANTATION WAS LITTLE LOWER IN DAYTIME AND WAS LITTLE HIGHER AT NIGHT.LIGHT INTENSITY DECREASED RAPIDLY IN THE PLANTATION AT ABOUT 10M DISTANCE FROM THE EDGE OF THE CLEARED AREA. 2)THE HEIGHT OF TREES ADJACENT TO THE CLEARED AREA(CEDAR 10.2-11.1M,CYPRESS 10.3-10.8M) WAS 6 TO 14% LESS THAN THAT IN THE PLANTATION.HOWEVER,WHEN AREAS OF SIMILAR DENSITY WERE COMPARED,CEDAR ADJACENT TO THE CLEARED AREA HAD A TENDENCY TO BE LITTLE LOWER IN HEIGHT.WHILE CYPRESS SHOWED NO TENDENCY. 3)THE DIAMETER OF ADJACENT CEDAR(12.1-13.6 CM) DECREASEDSLIGHTLY COMPARED TO THAT IN THE PLANTATION.HOWEVER,NO DECREASE WAS SEEN WHEN DENSITY OF TREES WAS THE SAME.THE DIAMETER OF ADJACENT CYPRESS(15.1-17.4CM) WAS NOT OBSERVED TO DECREASE. 4)BIOMASS PER 150SQUARE M OFPLANTATION ADJACENT TO THE CLEARED AREA CALCULATED FROM HEIGHT,DIAMETER AND DENSITY OF TREES(TOTAL OF CEDAR AND CYPRESS) WAS 3.3 TO 3.5CUBIC M IN VOLUM AND 0.63 TO 0.7SQUARE M IN BASAL AREA OF TREES.BIOMASS WAS ALMOST SIMILAR TO THAT IN THE PLANTATION.

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