Two series of realised genetic gain tests of large plots, one for black spruce (Picea mariana (Mill.) B.S.P.) and one for white spruce (Picea glauca [Moench] Voss), were established in the early 1990s in New Brunswick, Canada, to investigate realised gains from planting improved seedlots representing early-stage tree improvement activities. Individual-tree growth was recorded up to age 15 (one-quarter of their rotation age). Four improved seedlots were included in the black spruce gain test. Planting the superior stand seedlot (CAN101) could obtain moderate gain (7.0% in volume/tree and 3.5% in volume/ha at age 15). Growth improvement for the seedlot (UNROG) collected from a seedling seed orchard (FRA_SSO) established using phenotypically selected plus trees was negligible but genetic roguing improved the FRA_SSO seedlot’s growth, resulting in 3.3 and 2.1% increase in 15-yr volume per tree and per hectare, respectively. The highest gain was observed by deploying the elite half-sib family (01-15), which resulted in a gain of 27.6% in 15-yr volume/ha. Three improved seedlots were included in the white spruce realised-gain test. The seedlot (OVSSO) collected from a provenance seedling seed orchard had 9.2% more volume/ha at age 15 years. Much higher gains were observed in the seedlots collected from an unrogued clonal seed orchard (DNR_CSO). Mixed cone collections from the DNR_CSO achieved 25.6% more volume/ha at age 15 than the unimproved seedlot. Practicing supplemental mass pollination with unimproved pollen in the DNR_CSO greatly reduced its seedlot gains, i.e. 12.9% in 15-yr volume/ha. In both tests, the gain varied with age or site index. Realised gains in this study differed greatly from those observed in the corresponding genetic tests using small- plots. This suggests that using a small plot size for trials could greatly bias the actual gains possible on a plantation-scale, particularly when using seedlots obtained from orchards.
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