Though stone pine is currently a genuine forest tree of Mediterranean ecosystems, its use as grafted orchards crop for its edible pine nuts is potentially feasible. Therefore, genetic improvement of the species has been undertaken by several Spanish forest administrations, establishing in the Nineties experimental clonal orchards by grafting scions from plus trees, selected for their outstanding cone yield in pine forests of the main Spanish provenance regions. This paper analyses the coming into production of four clonal trials located at the National Forest Breeding Centre «Puerta de Hierro», Madrid. The four different-aged orchards showed a strong, synchronized masting habit. Estimations are given for the degree of genetic determination of cone production and for clonal improvement values. Due to the presence of strong size-yield correlations and spatial autocorrelations, genetic parameters were estimated by an individual tree cone-yield model adjusted for environmental tree size differences and for correlations between nearest neighbours (NN). The degree of genetic determination H2, estimated in less than 20% without adjustments, reached 30-38% adjusting for environmental size variation and 45-73% after spatial adjustment, with parallel increments in clonal improvement values and expected genetic gain. The results allow rogueing the four clone banks, progressing in the domestication of the stone pine as nut crop.