Breeding seed orchards (BSOs) or seedling seed orchards (SSOs) comprise seedlings from selected trees in different provenances, but could also include seed lots from provenances. A family from a selected tree is known as an open pollinated family (OP-family). BSOs aim to provide improved germplasm after selection, but also serve as test sites of different seed sources.

It is not only important to avoid inbreeding depressions, but one should also seek to retain sufficient genetic diversity in BSOs in order to achieve continued genetic gains in the next breeding generations through recombination (see Ericsson et al. 2013). This issue is addressed in Part II: Analysis and selections in BSOs. This first part presents guidelines on data collection, selection of traits to be measured and methods used to assess the traits of interest.