Variability of Mediterranean Stone pine cone production: Yield loss as response to climate change

Cones are harvested from Mediterranean Stone pine Pinus pinea L. for their edible kernels, pine nuts, which have been used as a food item in the region since Palaeolithic times. At present, cone yields render higher incomes to the owners of these pine forests than any other forest product. The large annual variation of cone yields is an important issue for forest management planning, which requires further research in order to establish its causes. One of the simplest explanations given for masting habits in polycarpic plants is that of weather tracking. Many plant ecologists, however, consider that this theory is insufficient and that further causes should be investigated. In this context, the present study analyses historical weather and yield registers over 41 years in one of the world's main Stone pine areas, the Northern Inland Plateau of Spain. Significant relationships found between rainfall and temperatures at certain key periods during the 4-year cone development period allowed for a multiple linear regression model for the log-transformed annual cone yield to be set up. This also included a negative autocorrelation with the ripening cone load during strobili induction. The model accounts for 75% of total variance between years. The observed trend of cone-yield reduction from 180 to less than 100 kg ha−1 in the last 40 years was slightly overestimated by the predicted effects of the covariables that show significant tendencies to a warmer and drier climate.