Genetic variation in Sitka spruce (Picea sitchensis (Bong.) Carr.) regarding height growth, stem form and frost hardiness at the provenance, progeny, and clonal level, based on Danish field trials

altura arbre plus clone clones danemark denmark descendance dinamarca durcissement endurecimiento forma arborescente frost gel genetic variation hardening hauteur height helada picea sitchensis plus trees port arborescent procedencia progenie progeny provenance stems tallo tige tree form