Long-term influence of commercial thinning on stand structure and yield with/without pre-commercial thinning of spruce-fir in northern Maine, USA

•Long-term responses to commercial thinning (CT) in spruce-fir stands assessed.•Delaying CT in young spruce-fir stands did not enhance total yield and stand value.•Low and crown thinning enhanced average tree size and sawlog production.•Thinning from above had detrimental effects on tree size and total yield.•Similar cumulative volume after light crown or low thin and in unthinned stand.