New Zealand Journal of Forestry Science

Abstract

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 (FRASSO) established using phenotypically selected plus trees was negligible but genetic roguing improved the FRASSO seedlots 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 (DNRCSO). Mixed cone collections from the DNRCSO achieved 25.6% more volume/ha at age 15 than the unimproved seedlot. Practicing supplemental mass pollination with unimproved pollen in the DNRCSO 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.