Variation in effective number of clones in seed orchards

The effective number of clones (N-c) was estimated for 255 conifer clonal seed orchards in Finland, Korea, and Sweden, based on the variation in the number of ramets among clones. The mean census number of clones (N) varied from 70, in 13 Korean Pinus koraiensis seed orchards, to 139 in 176 Finnish Pinus sylvestris seed orchards. The mean effective number of clones (N-c) was 66, with a range from 10 to 421. One fifth of the orchards had N between 10 and 40, and two thirds between 41 and 160. On average, the relative effective number of clones (N-r = N-c/N) was 0.74, with a range from 0.2 to almost 1.0. Thus, the census number of clones in a seed orchard is generally rather informative, but the effective number of clones is more informative. Many of these first-generation seed orchards were established with an intention to have near-equal numbers of ramets for each clone. The use of effective number of clones may be more important in future seed orchards and genetically thinned seed orchards.