Predicting climate-related compositional shifts in nut-producing species that are important for bears during hyperphagia

José Carlos Pérez-Girón^1*José Vicente López-Bao²Emilio Díaz-Varela³Pedro Álvarez-Álvarez⁴

• ¹University of Granada, Granada, Spain
• ²Biodiversity Research Institute, University of Oviedo-CSIC-Principado de Asturias, Mieres, Spain
• ³Higher Polytechnic School of Engineering. University of Santiago de Compostela, Lugo, Spain
• ⁴Department of Organisms and Systems Biology, Polytechnic School of Mieres, University of Oviedo, Mieres, Spain

Climate change represents an escalating threat to wildlife globally, disrupting ecosystems and altering species interactions. Key nut-producing forest species in the Cantabrian Mountains may be affected, with consequences for Cantabrian brown bears (Ursus arctos) during hyperphagia. Understanding such changes may help to improve conservation strategies to ensure that bears may be able to adapt to changing environmental conditions. With this aim, we assessed the current and future habitat suitability of all nut-producing trees in the Cantabrian Mountains. We fitted species distribution models using a down-sampling random forest ensemble approach to create comprehensive maps and species flows, identifying key hotspots of nut production under the SSP3-7.0 and SSP5-8.5 climate change scenarios.Based on bear mobility patterns, we identified areas where individuals lacked access to at least two fruit-producing species, thereby identifying potential areas of nuts shortage for bears during hyperphagia. We anticipate a potential decline in beech (Fagus sylvatica) and Atlantic oaks (Quercus petraea), with a compositional shift towards thermophilic species, such as sweet chestnuts (Castanea sativa) and Mediterranean oaks (e.g. Quercus ilex). The area unsuitable for any nut-producing species is likely to increase over time, reaching 25% % within the current bear range. The diversity of nut-producing species is projected to decline over time, leaving large areas within the bear's range with access to only one or two species. Bears may be able to gain access to food resources owing to their dietary plasticity and their ability to move and track energy-rich food resources. Ensuring the long-term accessibility of nuts to 3 bears in some areas could be based on the establishment of Chestnut plantations apart from human settlements, as well as actions to enhance fruiting for oaks, such as the case of Pyrenean oaks.• Climate change can impact the survival and productivity of nut-producing species.• In some regions, brown bears feed mainly on nuts during hyperphagia.• Bear adaptability and mobility may ensure future access to nut-producing species.• Chestnut plantations far from humans may favour bears' access to chestnuts.• Actions to enhance fruiting for oaks could improve nut availability in some areas.