Search

Within the framework of a series of forest recovery researches of a subtropical evergreen broadleaved forest, this study was carried out to measure mortality rates of tree stumps changed by species diameter at breast height (DBH) based on the surveys of 62 woody species and 1,893 tree stems taller than 1.2m in four 20m X 10m plots were recorded in 1993. At an August 1998 tree census five years after clearcut, all sprouting stems higher than 1.0m were identified, and the statuses of all the residual stumps were checked. The investigation showed that 382 stumps were dead without any living sprouts whereas 1,511 stumps were survived with living sprouts. The further studies showed that the mortality rates of stumps did not vary with DBH of the stand, but vary with the species DBH remarkably. The mortality rates by stump DBH within species for these whose total stump numbers ≧10 stems in the study plots were divided into four patterns: (a) With the increasing DBH, the mortality rates increased, (b) Inversely, with the increasing DBH in a certain extent, the mortality rates decreased, (c) With an increasing DBH, the mortality rates decreased at first and then increased to some extent, (d) The mortality rates were independent of DBH. The above results suggested that different species might have different mortality patterns, and that different tree species might have different rational DBH ranges for sprout natural regeneration. This knowledge could be much useful for forest recovery forecasting when the severe forest disturbances occurred in subtropical regions., 本研究は、亜熱帯常緑広葉樹林の森林回復に関する研究の一環として、1993年に沖縄島北部の琉球大学農学部与那フィールドの林地に設置された試験地を対象に、皆伐施業5年後の1998年に根株の生育と毎木調査を実施した。今回は主として、根株の生育、とくに枯死状態について報告する。皆伐施業試験地では、設定された天然林当時の樹高1.2m以上の立木62樹種、1,893個体のうち、382個体の根株が枯死し、1,511個体の根株に萌芽が認められた。根株の枯死率は、全個体で胸高直径間には明確な差がなく、樹種別の胸高直径間に差がみられた。根株個体数が10個体以上の33樹種別および胸高直径別の根株枯死率は4型に類別された：(a)胸高直径の増加にともなって枯死率も増加した（カクレミノ､タイミンタチバナなど7種）；(b)胸高直径の増加にともない一定の直径範囲で枯死率が減少した（イヌガシ､イタジイなど9種）；(c)胸高直径の増加にともない枯死率は初め減少し、その後増加した（サクラツツジ、ヤブツバキなど4種）；(d)枯死率は胸高直径と関係がなかった（イジュ、ツゲモチなど13種）。萌芽力に対して、根株枯死率の類型別に異なることが示唆された。