Terpene synthase (di-TPS) involved in the biosynthesis of diterpene natural products included in conifer oleoresin secretions and volatile emissions; these compounds contribute to biotic and abiotic stress defense against herbivores and pathogens (PubMed:21385377). Catalyzes the conversion of (+)-copalyl diphosphate ((+)-CPP) to isopimaradiene (PubMed:21385377). (+)-copalyl diphosphate = abieta-8(14),12-diene + diphosphate (+)-copalyl diphosphate = abieta-7,13-diene + diphosphate Secondary metabolite biosynthesis; terpenoid biosynthesis. Terpene metabolism; oleoresin biosynthesis. Accumulates in apical leaders upon wounding in both resistant and susceptible to white pine weevil (Pissodes strobi) plants. The Asp-Xaa-Asp-Asp (DXDD) motif is important for the catalytic activity in the class II active site relevant for the cyclization of GGPP. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity in the class I active site, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsd subfamily.