Advanced generation seed orchards' turnover as affected by breeding advance, time to sexual maturity and costs, with special reference to Pinus sylvestris in Sweden

The effect of various biological, genetic, economic and management factors relevant to advanced generation seed orchard establishment was investigated using numerical estimates for Scots pine (Pinus sylvestris L.) in Sweden. Factors considered were planting density, rate of genetic advance in the breeding population, timing of first seed collection, seed value, seed production cost (stratified to establishment, annual management, cone harvest and seed extraction), orchard rotation age and contamination level. The developed model demonstrated its utility in studying and evaluating various economic and biological options associated with advanced generation seed orchard establishment/turnover. Sensitivity analyses demonstrated the robustness of the developed model through various arbitrarily changes in genetic gain advances, establishment, management and seed production, particularly those associated with cone harvests from upper crown and costs. The Swedish Scots pine case study produced results supporting faster turnover of seed orchard generations (30 vs 40 years) with shorter orchard lifespan (early start of seed cone after 8 years vs 15 years) delivering higher gain through minimizing the genetic gain differential between the breeding and production populations and allowing the capture of this gain for inclusion in the seed orchards. Orchard planting densities of 400 and 600 grafts per hectare produced similar results with marginal differences, and the latter was recommended for future orchard establishment.