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We studied the latitudinal and altitudinal variations in composition and species richness of trees in 24 plots across temperate to subtropical regions from southern Kyushu to the northern Ryukyu Archipelago, Japan. Cluster analysis based on presence/absence of species in 0.25-ha segments of the plots identified three forest zones reflecting climate and geohistory: cool-temperate mixed conifer-broadleaf forest (MF) north of the Tokara Gap (Kyushu and Yakushima), warm-temperate evergreen broadleaf forest (EBF) north of the Tokara Gap, and subtropical EBF south of the Tokara Gap (Amami-Oshima, Tokunoshima, and Okinawajima). The MF zone corresponded to Kira's Warmth Index (WI) < 100°C. The two EBF zones overlapped in the range of WI, and thus their boundary was determined by geohistory rather than by climate. Plot-level species richness per 400 stems increased with increasing WI, with decreased values in Yakushima, suggesting that geohistory (isolations from Kyushu as well as by the Tokara Gap) depressed the species richness of Yakushima. Greater species richness in the subtropical EBF was explained by the presence of species whose distributions were restricted to the south of the Tokara Gap, indicating that the size of tree flora influences the plot-level species richness. By contrast, lower species richness of MF in Yakushima than in Kyushu was due to the absence of species whose distributions were restricted to Kyushu northward, indicating the impoverishment of the cool-temperate flora of Yakushima. In conclusion, climate and geohistory shape the tree-community composition and diversity of old-growth forests in this transitional zone from temperate to subtropical regions.

Cast Mg 85 Y 9 Zn 6 has an 18R-type LPSO structure. However, Mg 85 Y 9 Zn 6 recovered after being subjected to a loading pressure of 7 GPa at 973 K shows a fine dual-phase structure composed of a face-centered cubic (fcc) structure showing a superlattice (D0 3 ), as well as a hexagonal close-packed structure (hcp:2H). The D0 3 /hcp structure transformed to 18R-type LPSO during heating at ambient pressure. In this research, the transformation process from the D0 3 /hcp structure to 18R-type LPSO structure was discussed by means of in situ XRD and first-principles calculation. At first, lattice volume of 2H increased with an increase in the temperature, because of the Zn and Y emitted from the D0 3 phase into the 2H lattice. After the volume expansion of 2H lattice, the structure collapsed due to insert of random stacking faults (SFs). Then, a formation of 18R-type LPSO structure occurred. Based on a first-principles calculation for pure Mg, volume expansion of the 2H lattice causes the transformation to an 18R structure. Furthermore, the results of free energy calculations for the hcp and fcc structures in the MgYZn ternary system show that the segregation of Y and Zn atoms on SFs occurs by the Suzuki effect. These segregated Y and Zn atoms in SF layers, which have a local fcc structure, create a synergy between the stacking and chemical modulations. Present result insists that the volume increase of 2H lattice takes place first, and then the transformation from the hcp structure to 18R stacking occurs. [