Potential Factors behind the Decline of Pinus pinea Nut Production in Mediterranean Pine Forests

Abstract

Mediterranean stone pine nut is appreciated for its high economic and nutritional value. Starting in 2012, Pinus pinea nut production declined throughout the Mediterranean area. The dry cone syndrome associated with this decline and the introduction of Leptoglossus occidentalis occurred simultaneously. This study aims to evaluate potential reasons behind the decline in pine nut production in Lebanon, considering climatic factors and the invasion of L. occidentalis. Correlation analysis was used to examine a potential relationship between cone yield and the percentage of damaged seeds per cone. Climatic variables were also tested. Two time periods were considered for analysis: before and after 2012. Cone production and the percentage of damaged seeds were negatively correlated (r = −0.42). From 2012 to 2017, cone production declined by 50% and the percentage of damaged seeds increased on average from 3% in 2012 up to 60% in 2017. Correlations were detected between cone production and the temperature of the hottest three months of the year of harvesting, and between cone production and average temperatures during the year of cone initiation. A conjunction of factors that include L. occidentalis and climatic factors might have affected the pine nut production in Lebanon.