Variation in effective number of clones in seed orchards

The effective number of clones (N-c) was estimated for 255 conifer clonal s eed orchards in Finland, Korea, and Sweden, based on the variation in the n umber of ramets among clones. The mean census number of clones (N) varied f rom 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) w as 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 eff ective number of clones (N-r = N-c/N) was 0.74, with a range from 0.2 to al most 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 inte ntion to have near-equal numbers of ramets for each clone. The use of effec tive number of clones may be more important in future seed orchards and gen etically thinned seed orchards.