Climate change impacts on the Mediterranean biogeographic patterns of macrofungal diversity

Abstract Macrofungal diversity plays a central role in forest ecosystem functioning, contributing to nutrient cycling, plant performance, and food web dynamics. Despite its ecological importance, spatially explicit assessments of macrofungal diversity remain scarce due to limited long-term data. Here, we combine one of the largest plot-based datasets of macrofungal fruiting body abundance with machine learning models and high-resolution climate data to quantify current and future biogeographic patterns of macrofungal alpha and beta diversity across pine forests in Catalonia, a western Mediterranean region spanning a broad altitudinal and bioclimatic gradient. Our results indicate that climate change will differentially affect fungal communities across environmental gradients, leading to declines in species richness and abundance-weighted diversity (alpha diversity), particularly at higher elevations, while the strongest shifts in community composition (beta diversity) are projected at lower elevations. These changes are highly dependent on greenhouse gas emission scenarios, with severe impacts under high-emission pathways and limited effects under mitigation scenarios. Importantly, we show that macrofungal responses vary among ecological lifestyles. While both mycorrhizal and saprotrophic fungi are projected to decline in alpha diversity in cooler environments, saprotrophic taxa may increase under warmer conditions at lower elevations. Overall, our findings highlight the sensitivity of macrofungal communities to climate change and provide novel insights into how future warming may reshape fungal diversity patterns and trophic structure across Mediterranean ecosystems.