Density Effects on the Conifer Mortality in Declining Spruce-fir Forest in Northern Japan : Implication of Bark Beetle Attack to, Cause Spruce Decline

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We examined mortality patterns of two conifer species in relation to tree abundance and species composition in a declining sprucefir forest in Akan National park, Hokkaido, northern Japan. The data taken from eleven 58 m×58 m square study plots showed that percentage basal area (BA) of dead trees of canopy trees during the last decade was 49% for Picea jezoensis (Sieb. et Zucc.) Carr and 30% for Abies sachalinensis (Fr. Schm.) Masters. In P. jezoensis, percentage basal area (BA) of dead trees was positively related to both BA of its own species and proportion of it to BA of all species, whereas it was not significantly related to both of these variables in A. sachalinensis. Multiple logistic regression with dbh as a confounding factor also indicated that, in P. jezoensis, the proportion of dead stems was positively affected by the stem density of conspecific trees, whereas it was negatively affected by the stem density of the other species in each study plot. However, in A. sachalinensis, the proportion of dead stems was significantly related to neither of these factors. The different mortality pattern between two conifer species suggests that the spruce bark beetle, Ips typographus (L.), which is a serious pest of spruce, may have caused the P. jezoensis decline. Instead of wind-throw or thinning that usually initiate this bark beetle attack, some unknown factors seemed to predispose the trees to insect attack. These unknown factors may also explain the high mortality of A. sachalinensis in this forest.
1998-11-16

Density Effects on the Conifer Mortality in Declining Spruce-fir Forest in Northern Japan : Implication of Bark Beetle Attack to, Cause Spruce Decline

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