Variability and trends of black truffle production in Spain (1970-2017): Linkages to climate, host growth, and human factors

Black truffle (Tuber melanosporum) is a highly-appreciated fungus that grows below ground during several months, undergoing a series of morphogenetic stages before it is harvested in late autumn or winter. Black truffle production in Spain has been subject to important temporal variation in recent decades. The records of the Spanish Truffle Growers Association from 1970 to 2017 were analysed using additive models to investigate the relative roles of climate, host tree growth and other environmental and human factors on the variability and trend of fruiting body production and phenology. Climatic factors largely explained the variability in annual truffle production, but not the major time trend observed in the studied period. Temperature and precipitation during fruiting body development showed the highest relationship with truffle production. Atmospheric evaporative demand during fruiting induction and temperature during maturation showed a significant relationship to how truffle production was distributed throughout the fruiting season. The relationship between truffle production and host growth was mostly explained by summer rainfall and by temperatures in several periods spanning from host tree bud burst to fruiting body ripening. The temporal trend of Spanish truffle production in the last decade reflected the recent transition from a wild harvest to an agricultural production, with an abrupt increase in annual production and a decrease in year-to-year variability. In the context of the expected evolution of regional climate according to current models, our results point to drier and warmer summer conditions as major threats to truffle production in Spain. Spring and autumn warming could induce an advance in the mean day of truffle fruiting.