Variations in ring width and ring coloration of 89 spruce trees from six sites in the Lotschental, Switzerland, are analyzed. Sites are located along an altitudinal transect spanning 1500 to 2000 m a.s.l. on a SSE- and a NNW-facing slope. Site ecology is further determined by local differences in micro relief, allowing differentiation into locally wet and dry sites. Growth reactions are classified as "site pointer years" representing extreme years common within a site, and as "valley pointer years" representing extreme years common between sites. These site and valley pointer years are classified and analyzed separately for ring width, light rings and dark rings. In so doing, 44 ring width and 9 light ring pointer years are reported for the 20th century. Dark rings do not crossdate within sites, so that no such pointer year is documented. Comparisons with instrumental data show that May precipitation and temperatures are crucial for both negative and positive ring width pointer years. Climate variability in all other months only modifies the intensity of these pointer years. Light ring pointer years correlate with low temperatures recorded towards the end of the growing season, particularly in September. Keywords: Climate, tree ring, light ring, pointer year, site ecology, spruce, Switzerland
