Density effects on the conifer mortality in declining spruce-fir forest in northern Japan: Implication of bark beetle attack to, cause spruce decline

We examined mortality patterns of two conifer species in relation to tree abundance and species composition in a declining spruce-fir 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% forPicea jezoensis (Sieb. et Zucc.) Carr and 30% forAbies sachalinensis (Fr. Schm.) Masters. InP. 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 inA. sachalinensis. Multiple logistic regression with dbh as a confounding factor also indicated that, inP. 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, inA. 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 theP. 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 ofA. sachalinensis in this forest. This research was supported by FFPRI Project, Ministry of Agriculture, Forestry and Fishery.     

Stand structure and establishment process of an old-growth stand in the mixed deciduous broadleaf/conifer forest of Mt. Moiwa Forest Reserve, central Hokkaido, Northern Japan

Stand structure of an old-growth forest was studied by tree (≥4.0 cm in DBH) census in a main plot of 1.3 ha and 8 additional plots (0.525 ha in total) located in the Mt. Moiwa Forest Reserve, central Hokkaido, northern Japan. Major tree species with ≥1.0% of the relative basal area and of relative number of trees (Acer mono, A. mono var.mayrii, Kalopanax pictus, Magnolia kobus var.borealis, M. obovata, Prunus ssiori, Tilia japonica, andUlmus laciniata) have positive values of skewness in DBH, which shows the abundance of smaller-sized stems. All stems over 1.3 m high in the main plot were mapped to clarify the relationship between stem densities and canopy states. Although advances from sapling (>1.3 m tall and <4.0 cm DBH) to small tree (10.0 cm ≤ DBH <25 cm) for all major component species, exceptP. ssiori andU. laciniata, were independent of canopy states, those ofP. ssiori andU. laciniata depended on canopy gaps.Betula spp. was the most abundant gap makers, butT. japonica andA. mono (including var.mayrii) were dominant species in the main plot. This suggests the shift of dominant species in the forest of the study site. Historical records of disturbance demonstrated that selective cuttings of conifers during the late 19th century were responsible for the dominance ofBetula spp. and the subsequent shift of dominant species. This fact suggests that artificial disturbance plays an important role in the establishment ofTilia japonica-Acer mono forest considered to be a climax of the mixed deciduous broadleaf/conifer forests.