Predicted gains from Sitka spruce seed orchards

The most recent predicted genetic gain figures for the Sitka spruce clonal seed orchards are listed below. These gains are based upon the measured performance of their component clones over unimproved direct import Queen Charlotte Islands material, assessed at 15 years old.

Identity numbers

Until recently the identity numbers of seed orchards looked like this e.g. SS  12. They now look like this e.g. psiOR12TE, due to changes brought in under the Forest Reproductive Material Regulations (2002), which came into force in Britain in January 2003:

Note that:

  • ‘QU’ indicates that a proportion or all of the parents represented in the orchard were selected for their phenotypic superiority only
  • ‘TE’ indicates that the parents represented in the orchard have been proven to produce superior progeny in comparative field tests.

Predicted genetic gains

Sitka spruce clonal seed orchard predicted genetic gains
  Predicted percentage gain over QCI
Orchard number and name Years planted Diameter Density Stem Form
psiOR11QU (Slebech) 1980-1984 18 -10 9
psiOR12TE (Ledmore) 1982-1983 20 -6 10
psiOR13TE (Ledmore) 1984-1985 21 -12 9
psiOR14TE (Shobdon) 1986 21 -8 5
psiOR16TE (Newton) 1986-1991 10 -2 8
psiOR17TE (Meeroak) 1988-1990 21 -11 8
psiOR18TE (Rogate) 1989-1990 21 -10 5
psiOR19TE (Lobslack) 2002 22 -1 16
psiOR20TE (Bruxburn) 2004 17 0 22
psiOR21TE (Elson) 2008-2010 14 4 20

See disclaimer below.

Further information

Sitka spruce clonal seed orchards are unlikely to produce marketable quantities of seed until approximately 10 years from planting.

See also Predicted gains from Sitka spruce parents of families (family mixtures).

For more information on seed orchards please contact Steve Lee


The predicted gain figures presented above assume:

  • No contamination from rogue pollen originating from outside the seed orchard;
  • An equal contribution of male and female flowers from all the constituent tested clones (a situation know as 'panmixis).

All seed orchards were originally planted on sites suitably isolated from stands of the same or hybridizing species but this may have changed with time. Also in practice panmixis is rarely likely to happen although in good flowering years when most of the clones appear to be flowering, it is unlikely that there will be significant deviation from the predicted gain figures. In years of poor flowering when only a few clones are dominating the production of male and female flowers, there could be considerable deviation from the predicted gain figures.

Forest Research does not own any seed orchards and bears no responsibility for deviations from predicted gain figures as a result of contamination by rogue pollen or seed collections during years when clones are not approaching panmixis. It is the responsibility of the purchaser of these seed or trees raised from these seed to make enquiries of the vendor or seed orchard owner regarding possible rogue pollen sources and the flowering rate during the year of collection. Details of seed orchard location and ownership are available in 'The National Register of Basic Material' which can be viewed in the Forest Reproductive Materials section of the Forestry Commission website: