Fluctuating beech mast drives spatial behavior and damage risk in brown bears

Mast seeding, the variable and intermittent production of seeds by trees, generates strong temporal fluctuations in food availability with cascading effects on wildlife behavior and ecosystem functioning. This study examines how mast seeding of European beech (Fagus sylvatica L.) influences the spatial behavior of brown bears (Ursus arctos) in the Italian Alps. Using a combination of historical records and field sampling, annual beech seed biomass was estimated and mapped for the Province of Trento over a 15-year period (2007–2021). The energetic value of beechnuts was quantified in laboratory, providing an estimate of the caloric resources available to bears. These data were integrated with records of bear-related damages and GPS telemetry from 16 individuals to assess bear responses at both home-range and landscape scales. Standardized damage to beehives and livestock declined markedly during mast years, indicating reduced reliance on anthropogenic food sources when natural resources were abundant. Conversely, during beech crop failures, bears increased their use of agricultural areas and reduced their use of beech forests, reflecting behavioral flexibility in response to resource scarcity. At the landscape level, damage risk was highest in agricultural and pasture areas located near beech forests and far from urban centers. By linking mast seeding dynamics, bear movement patterns, and damage occurrence, this study highlights how inter annual variability in key food resources shapes brown bear behavior. The results provide a spatially explicit framework to anticipate conflict risk and support adaptive management strategies.