Predicting porcini: a decade of sporocarp monitoring reveals the meteorological triggers of Boletus edulis fruiting in central European beech forests

The reproductive biology of ectomycorrhizal fungi (EMF) is difficult to study because sporocarp formation cannot be reliably induced under laboratory conditions. This limitation partly reflects our incomplete understanding of the short-term meteorological conditions that trigger fruiting in most EMF species. To address this knowledge gap, we analyzed a decade-long (2015-2024) dataset of near-exhaustive sporocarp observations from a long-term monitored population of the prized edible fungus Boletus edulis in a typical central European beech forest near Bielefeld, Germany. We used two-dimensional kernel density estimation to investigate how temperature and precipitation during the five days preceding fruiting influenced sporocarp formation, before deriving the optimal conditions associated with fruiting with a generalized linear mixed effect model. Our results indicate that while sporocarps can form across a broad range of temperature and precipitation combinations, fruiting is maximized at an intermediate temperature of 13.2 degrees Celsius and increases linearly with precipitation. Consequently, under projected warmer and dryer autumn conditions, sporocarp formation in European beech forests is likely to decline.