MASTHING: a process-based model of mast seeding in European beech

Simone Bregaglio , Sofia Bajocco, Carlotta Ferrara, Michał Bogdziewicz, Andrew Hacket-Pain, Francesco Chianucci

Masting, the synchronised interannual variation in seed production, shapes forest regeneration and many ecosystem processes, yet process-based models remain underdeveloped. Here we introduce MASTHING (MASting THeory modellING), an individual-tree model coupling phenology, carbon gain, resource storage, temperature cues, and environmental vetoes on reproduction. We parameterised MASTHING for European beech (Fagus sylvatica L.) using 43 years of data from 100 trees across 11 sites in England to test alternative hypotheses about masting mechanisms. Three formulations were compared: resource budget only (RB), and extensions with additive (RB+WC) and interactive (RB×WC) temperature cue effects. Performance improved with complexity and was highest when cue sensitivity depended on internal resource status. At the site-year scale, explained variance increased from R2 = 0.58 (RB) to R2 = 0.76 (RB×WC), supporting that favourable cues trigger strong reproduction only when sufficient resources have accumulated. The model reproduced mast and failure years, partly captured long-term breakdown in masting intensity under climate warming, and broadly predicted seed production during 2023-2025, although low-seed years were less well predicted. Modelled resource and cue dynamics were sufficient to simulate short-term variation and progressive weakening of reproductive pulses. MASTHING provides a platform for testing masting hypotheses, evaluating climate change impacts, and supporting operational seed forecasting.