Female fertility variation in mature Pinus sylvestris clonal seed orchards

Female fertility is the basis for the output of seeds from clonal orchards and its variation is of major interest for the economics and biology of seed orchards, especially for the efficiency and diversity of seed orchard crops. Assessments of female fertility variation in 10 mature (>15 years old) seed orchards of Scots pine (Pinus sylvestris L.) were evaluated and compared. Depending on the individual orchard, fertility variation for each clone was assessed in slightly different ways, e.g. number of strobili, cones, seeds or litre of cones per ramet. Assessments in five of the orchards were made over consecutive years. The main result was that the clonal variation in mean female fertility per surviving ramet was lower than expected from the literature; the Kang-Lindgren sibling coefficient (Ψ) within individual years averaged 1.35. The variation between ramets within clones and years was of similar magnitude as that between clones. Clone by year interactions were noticeable, but were slightly lower than the variation between as well as that within clones in individual years. There was considerable variation in the variance components between years. The limited variation in female fertility indicated that it should not be a selection criterion when selecting clones for a seed orchard. Furthermore, it will not result in large differences between clones in seed set or large reductions in gene diversity in productive Scots pine seed orchards.