Influence of the age of parent stand on selected physical properties of Norway spruce seeds

The objective of this study was to determine the influence of the age of parent tree stand on selected physical properties of Norway spruce seeds to improve the efficiency of seed separation processes. Seeds were harvested in a forest complex located in the seed zone No. 202, in the municipality of Kruklanki in the Borki Forest District (N Poland) during mast years (1999, 2004, 2007 and 2012). The experimental material comprised of Norway spruce seeds from three differently aged tree stands (86, 119 and 129 years old in the first harvest year). The following measurements were performed for each seed: terminal velocity – with a pneumatic classifier; length and width – with a laboratory microscope; thickness – with a thickness gauge; angle of external friction – on an inclined plane, in two positions on a steel friction plate, and mass – with a laboratory scale. The results were used to calculate the arithmetic and geometric mean diameters, aspect ratio, sphericity index and density of seeds. The values of the analyzed properties were compared with ANOVA for factorial designs and linear correlation analysis. The results of the study indicate that Norway spruce seeds obtained from cones harvested in 2012 are characterized by the highest thickness and, consequently, by the highest values of the aspect ratio and sphericity index. The age of parent trees significantly influences the majority of physical properties of seeds. However, the patterns of observed changes are difficult to interpret due to the impact of weather conditions and the genetic potential of parent trees, which perform differently in response to changing climate and geomorphological conditions. Over the analyzed 13−year period a gradual increase was noted in the width, geometric mean diameter, aspect ratio and sphericity index of seeds, whereas the length and density of seeds decreased. Therefore, Norway spruce seeds should be separated mostly with the use of mesh screens with longitudinal openings, pneumatic separators and graders. The use of those devices, separately or in combination, for sorting Norway spruce seeds into mass fractions could contribute to more uniform seedling emergence when every seed fraction is sown separately