Catalyzes the initial cyclization step in the biosynthesis of ginkgolides, a structurally unique family of diterpenoids that are highly specific platelet-activating-factor receptor antagonists. Bifunctional enzyme that catalyzes two sequential cyclizations of geranylgeranyl diphosphate (GGPP) to levopimaradiene. (2E,6E,10E)-geranylgeranyl diphosphate = (+)-copalyl diphosphate (+)-copalyl diphosphate = abieta-8(14),12-diene + diphosphate Binds 3 Mg(2+) ions per subunit. Optimum pH is 7.2. Terpene metabolism; ginkgolide biosynthesis. Expressed in roots. 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.