Summer Plant Culling Criteria of Interior Spruce: Keeping the Bad and Throwing the Good?

Morphological criteria by which spruce nursery stock, or any conifer crop is culled generally raises discussion at the nursery gate. The discussion does not focus on the bulk of the crop but on those seedlings just over or under height and diameter limits. In British Columbia, some workers believe that `good' small seedlings are being culled in favour of tall `poor' stock. To address some of these concerns, standard and substandard (culls) blackout treated spruce stock derived from three seed origins (registered natural stand, registered seed orchard and full-sib controlled cross) was summer planted at Red Rock Research Station (RRRS), near Prince George, BC in early July 1993. RRRS is an uncompetitive environment. Very liberal grading criteria were used (the plug must hold together and the seedling should be taller than 9 cm) when this crop (16 of the 26 seedlots were of seed orchard origin) was lifted at RRRS. 1752 seedlings were planted and they were monitored during 1993 and into the 1994 season. Height and root collar diameter (RCD) of all seedlings was measured at planting and in September 1993. Seedlings were then classed as `culls' or `standards' based on morphology at planting according to B.C. Forest Service (BCFS) seedling specifications for interior spruce (Picea glauca, P.engelmannii and their naturally occurring hybrids) summer plant stock. Of the 781 seedlings classified as culls, 8.9 % were underheight, 7.9 % were overheight, 60.3 % had inadequate RCD, 20.5 % were underheight with poor RCD, and 2.3 % were overheight with poor RCD. Survival until June 1994 was excellent: greater than 98 percent regardless of class. Stem volume increment in 1993 was similar between cull and acceptable class seedlings but cull seedlings had significantly greater relative stem volume growth rates. These results raise concerns about present grading criteria for summer planting, particularly for seed orchard stock which tended to have smaller RCD. Further monitoring of the summer planted stock will be necessary to determine whether present grading criteria are in fact too conservative and should include some of the seedlings presently being culled. Growth patterns after planting were also examined in relation to seed origin and nursery treatment. Preliminary conclusions suggest that 1) seed orchard seedlots do not display unusual variability compared to natural stand seedlots, 2) blackout can effectively produce morphologically uniform seedlings suitable for summer planting programs and 3) blackout may promote abnormal terminal bud flushes. The cause and control of the latter issue remains to be ascertained. Otherwise, blackout is an efficient method to deliver quality seed orchard stock to the field for summer planting.

Download this file:

Download this file

Details

Author(s): Erica L. McClaren, Marek J. Krasowski, Christopher D.B. Hawkins

Publication: National Nursery Proceedings - 1994

Event: Combined Western Forest Nursery Association and the Forest Nursery Association of British Columbia
1994 - Moscow, ID