Influence of shelterwood density on survival and height increment of Piceaabies advance growth

A shelterwood experiment with eight different shelterwood densities was est ablished in southern Sweden in 1989. Advance-growth seedlings of Norway spr uce (Picea abies (L.) Karst.) were the focus of this study, in which damage , mortality and height growth were registered. Mortality was generally high , especially on clear-cuts and in low-density shelterwoods ( less than or e qual to 80 stems ha(-1)). Seedlings with a small initial size showed higher mortality compared with larger ones (> 50 cm). Mortality was caused by "re lease effects" (25%), pine weevils (Hylobius abietis L., 28%), and undeterm ined factors (47%). Mortality was attributed to "release effects" in cases where seedlings wilted in the first spring following cutting, and no other damaging agent could be detected. This damage was most frequent among seedl ings shorter than 20 cm on clear-cuts or in shelterwoods of low density. Th e most severe damage by pine weevils was Found in the same plots and was es pecially pronounced in seedlings 20-50 cm in height. Although frost frequen tly damaged seedlings (treatments less than or equal to 80 stems ha(-1)), n o seedling mortality was ascribed directly to frost. The mean annual height growth for 1989 -96 was greatest for seedlings that were largest at the st art of the experiment. For all seedling sizes, growth was highest at densit ies of 80-160 stems ha (1), whereas the optimum density for survival was ab out 160 stems ha(-1). Height, top-shoot length and top-shoot diameter the y ear before release cutting showed significant positive correlations with bo th survival and height growth for 1989-96.