Stone pine populations throughout the Mediterranean lack adaptative differentiation, but show high phenotypic plasticity. This reduced genetic diversity might be result of only recent expansion by man in historic times. Native at least on the Iberian Peninsula, its cones and edible seeds have been traded since Antiquity. It has been planted locally as ornamental, for land reclamation or for its edible kernel. Small rural groves and its presence as by-species in Mediterranean woodlands apart, forests dominated by stone pine are rare except single-layer stands planted in the last two centuries.
Mediterranean pine nuts are the most relevant nut from Mediterranean forests, collected in nearly 1 million hectares of stone pine forests or plantations, sparsely scattered from the Atlantic coast in Portugal to the shore of the Black Sea and Mount Lebanon. Spain, Portugal and lately Turkey are the main pine-nut producing countries. Annual global Mediterranean pine nut production is about 16-20,000 t nuts in shell (15-20% of harvested cone weight), i.e. 4-5,000 t kernels (only 4% of cone weight). But since 2012, supply of Mediterranean pine nuts has collapsed due to the expasnion and prevalence of a cone pest, the exotic Western Conifer Seed Bug, Leptoglossus occidentalis, that damages seeds and provokes seed and whole cone losses. As conseqence, the international wholesale price nearly doubled up to 40-45 €/kg for shelled kernel, the current retail price exceeding 70-100 €/kg.
Up to now, cones are still harvested mostly from forests, not orchard plantations. Even most new plantations aimed for pine nut production are managed as extensive forestry or agroforestry systems. Most trees are grown from unimproved seeds, not grafted varieties, and irrigation is rare. Nevertheless, the sustained demand on pine nuts exceeding supply has motivated initiatives of private landowners to promote intensively managed stone pine plantations as nut crop, especially in Portugal and Aegean Turkey, where benign climate favours sustained high per-hectare cone yields (several t/ha). In Portugal, in the last years stone pine has increased area several-fold to 175,000 ha, the same as in Turkey (195,000 ha).
Best-performing clones have been selected in different agro-climatic regions for stone pine as grafted tree crop. Since 2009, graft scions from a clone mixture of 64 Portuguese clones have been commercialised as ‘qualified’ forest reproductive materials. In 2015, 10 Spanish elite clones have been registered as ‘qualified’ basic materials, whereas 5 clones have even merited the category ‘tested’ basic materials, after demonstrating their superiority by comparative tests, evaluating their reproductive materials in grafted trials.
These improved genetic materials for Mediterranean stone pine allow for the establishment of grafted plantations, for a sustained production of pine cones and nuts as regular supply for regional value chains, support for regional rural development in Portugal, Spain, Turkey, Lebanon, or Tunisia. Additionally, for control of Leptoglossus occidentalis, Integrated Pest Management can be applied on orchards, whilst in European forest ecosystems, pesticide use is increasingly banned.
CONCLUSIONS: While new plantations in Portugal and Turkey are coming into production, cone yields from existing stone pine forests have collapsed in the last years, especially in Italy, Spain and Lebanon. Many of these old forests are facing huge challenges under global change: impacts of increasing droughts, prevalence of new pests like Leptoglossus occidentalis, senescence and lack of regeneration in absence of adequate management, wildfires, land use change. Profitability for forest owners and hence ultimately sustainability of this forest type is seriously jeopardised.