Fragmented forests, isolated fungi: Saproxylic polypores in boreal woodland key habitats

Forestry in boreal Sweden has significantly altered the landscape and reduced old-growth forests, promoting growth of younger, managed stands. Saproxylic polypores are in direct competition with forestry for resources and have declined significantly in diversity. These fungi play a crucial role in decomposing deadwood with their persistence reliant on habitat quality, connectivity, and continuous wood availability. We examined how log, stand, and landscape-level factors affect saproxylic polypore richness and community composition in 26 woodland key habitats (WKHs) in southern boreal Sweden. We recorded polypore fruitbodies on 1263 Picea abies deadwood units and assessed stand structure. GIS was used to quantify spruce forest amount and quality at 0.5, 5, and 15 km scales, including connections to larger high-quality habitats. Local-scale factors, especially deadwood volume and decay stage, strongly influenced fungal richness. Landscape effects were weaker, likely due to the homogenous and degraded surrounding forest matrix. However, polypore richness increased with high-quality forest cover at the 15 km scale, while medium-quality forest at 5 km had a negative effect. Red-listed species richness showed a strong eastward gradient, possibly reflecting historical forestry and extinction debt. Community composition patterns aligned with these trends, with further indirect effects from nearby forest amount and quality. We conclude that the landscape configuration matters but is context dependant. In our heavily managed study region, high-quality patches like WKHs are too isolated, leaving local conditions as the primary driver of fungal persistence. Effective conservation requires integrating landscape-scale measures, including identifying and protecting remaining forests with high natural values. • Log, stand, and landscape effects on polypores were studied in woodland key habitats. • Only small remnants of high-quality habitats remain in south boreal spruce forests. • Polypore communities were shaped by both stand and landscape-scale factors. • High-quality forests within 15 km increased red-listed and total polypore richness. • Historical logging impacts were reflected in current fungal species composition.