Balsam fir (Abies balsamea (L.) Mill.) – Red spruce (Picea rubens Sarg.) forest productivity 35 years after whole-tree and stem-only harvesting in north-central Maine, USA

•Whole-tree harvest has not reduced site productivity on this relatively fertile site.•35-year site productivity suggests whole-tree harvest is sustainable on this site.•Tree diameter increased after thinning but not biomass productivity.•Nitrogen fertilizer did not increase stand productivity.•Chesuncook catena soils may be able to support a bio-economy in northern Maine.