  (Abridged) We report on the environmental dependence of properties of
galaxies around the RDCSJ0910+54 cluster at z=1.1. We have obtained multi-band
wide-field images of the cluster with Suprime-Cam and MOIRCS on Subaru and
WFCAM on UKIRT. Also, an intensive spectroscopic campaign has been carried out
using LRIS on Keck and FOCAS on Subaru. We discover a possible large-scale
structure around the cluster in the form of three clumps of galaxies. This is
potentially one of the largest structures found so far in the z>1 Universe. We
then examine stellar populations of galaxies in the structure. Red galaxies
have already become the dominant population in the cores of rich clusters at
z~1, and the fraction of red galaxies has not strongly changed since then. The
red fraction depends on richness of clusters in the sense that it is higher in
rich clusters than in poor groups. The luminosity function of red galaxies in
rich clusters is consistent with that in local clusters. On the other hand,
luminosity function of red galaxies in poor groups shows a deficit of faint red
galaxies. This confirms our earlier findings that galaxies follow an
environment-dependent down-sizing evolution. There seems to be a large
variation in the evolutionary phases of galaxies in groups with similar masses.
Further studies of high-z clusters will be a promising way of addressing the
role of nature and nurture effects on galaxy evolution.
