K.S. KANG, A.M. HARJU, D. LINDGREN, T. NIKKANEN, C. ALMQVIST and G. U. SUH

 Variation in effective number of clones in seed orchards

This paper gives statistics on clone numbers for a large number of seed orchards, which is useful background for future discussions on this issue. The effective number of clones in clonal seed orchards, based on the number of ramets of individual clones, predicts the gene diversity from the seed orchard crop better than the census number of clones. The degree to which the effective number of clones is smaller than the census number depends on the inequality of the number of ramets among clones. Statistics from a large number of seed orchards inform decision-makers about how well the census clone number describes the seed orchards. As the clone number is the only commonly available statistic and often used for legal documents or guidelines, it is of importance to know how informative it is, based on a large number of real seed orchards. Numbers of ramets and clones are the most easily manipulated factors during establishment and thinning of a seed orchard, and an effective number can be used to predict the effect of such manipulations. The effective number of clones can be used to predict and monitor the effect of thinning of an existing seed orchard, to certify and describe orchards, and to consider the composition of new seed orchards. If the effective number is used instead of census number, the motive to have equal number of ramets per clone in a seed orchard vanishes. Effective number can also be optimally balanced with genetic gain; such a balancing would increase the genetic quality of seed orchard crops.

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_c 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.