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 t hree 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 rat e will be very high even in mature seed orchards. However, the contaminatio n rate in the thinned parts of the orchard was significantly lower than tha t 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 c lone were planted using a clonal-row design, and there were no significant differences in the outcrossing rates between the different parts of the orc hard.