Longer-term volume trade-offs in spruce and jack pine plantations following various conifer release treatments

We assessed growth responses 10 years post treatment for 31 combinations of site, species, and treatments from six studies in Ontario, Canada, to determine if conifer release treatments increase gross total conifer volumes but decrease gross total stand volumes in boreal forests. Treatments included single and multiple herbicide application or motor-manual and mechanical conifer release. Treatment effects on 10(th)-year gross total preferred conifer and total stand volumes ranged from -49% to +556% and -71% to +116%, respectively, compared to the untreated controls. We projected net merchantable stand volumes (NMV) from 10 years post treatment to 60 years of age. These projections indicate that NMV of preferred conifers at age 60 could range from 7.4 m(3) ha(-1) to 232.4 m(3) ha(-1). The variation in observed and predicted volumes can be attributed to site characteristics, tree species, ecology, and treatment efficiency.