Annual Variation in Pollen Contamination and Outcrossing in a Picea abies Seed Orchard

A mature Norway spruce [Picea abies (L.) Karst.] seed orchard, established in southern Finland with 67 clones from northern Finland, was analysed in three different years in order to estimate the pollen contamination ratios. Allozyme-based paternity analysis revealed that the contamination rate was high, 69-71%, and did not differ between the years studied. It appears that, in areas where spruce is the dominant tree species, the contamination rate will be very high even in mature seed orchards. However, the contamination rate in the thinned parts of the orchard was significantly lower than that in the unthinned parts in two of the three years studied. The outcrossing rate was also high, 96-100% in all years, even though the ramets of each clone were planted using a clonal-row design, and there were no significant differences in the outcrossing rates between the different parts of the orchard.