Modelling potential yield capacity in conifers using Swedish long-term experiments

•Yield capacity describing forest site productivity was expressed through site index.•Observations from permanent plots in long-term experiments give valid reference estimates of total volume production.•Variations in volume yield levels are explained in a larger extent by basal area levels.•The yield capacity functions can be used to compare tree species’ production under similar management regimes.•The functions offer far-reaching support for assessing climate change mitigation potential of boreal forests in northern Europe.