Phenotypic differences between plus-tree progenies of Sitka spruce (Picea sitchensis) and a comparison with Norway spruce (Picea abies)

Sammanfattning: Forest productivity and economic gains are two of the most important aspects to consider when managing forests these days. The performance of these depends on rotation periods and yields providing new opportunities to maximize earnings from the forest site and plant material. The selection of new species to plant in production forests is an option to address future climate changes. The use of other species, than Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), like Sitka spruce (Picea sitchensis (Bong.) Carr.) in an enabling environment can increase the overall production in the forest. The climatic conditions on the Western coast of Sweden are expected to be milder and warmer opening the opportunity to the use of Sitka spruce in the future. In favourable conditions in Southern Sweden, Norway spruce is able to produce around 8-10 m3'ha1'yr-1 whereas Sitka spruce in this field trial produced 16 m3'ha-1'yr-1. The increased use of improved plant material from different sources makes this difference even larger. This study used a field trial established by Skogforsk within a Sitka spruce breeding program. The identification and grouping of the best Sitka spruce plus-trees based on their progenies growth was done based on initial heights measurements at the age of 2 and 6. The estimations of heritability values showed low values between 14-17% for height (age 6), dbh (age 13) and wood density (age 22). Quality traits as forking, spike knots, branch diameter and wood density scores were assessed for the previous progeny groups, however, good quality traits were not linked to any specific progeny group. Most importantly, no assessed quality traits at year 22, contradicts the early selection by height at year 6. Wood density scores followed a decreasing trend with larger dbh growths, however, it was possible to select for plus-trees with large diameters and high density scores. Norway spruce trees, also present in the field trial, in comparison to Sitka spruce developed thinner branch diameters at breast height and higher values of wood density. Even so, Sitka spruce can be considered as a possible alternative to Norway spruce and Scots pine on the Western coast of Sweden for wood production.