Fungal Community Responses in Tiny Forests in Urban Areas in Germany 

Urbanization highly impacts soil properties and microbial communities in remaining soil patches. Tiny Forests, small densely planted native forest patches, represent an increasingly widespread nature-based solution to restore urban biodiversity. However, empirical data on their soil microbial communities remain scarce.In this study we assessed fungal communities in ten Tiny Forests and ten paired adjacent urban open spaces (control sites) in Berlin and Frankfurt, Germany, using DNA metabarcoding.We could show, that urban soils harbored high fungal diversity, with significant variation between Tiny Forests and control sites as well as among individual sites. Tiny Forests supported fungal communities specialized in decomposition and nutrient cycling, while control sites showed higher overall species richness. Community composition differed between Tiny Forests and control sites, yet site-specific patterns revealed that local environmental conditions highly shape fungal communities alongside land use effects.Taxonomic patterns indicated that differences between Tiny Forests and control sites were not limited to community structure but also involved shifts in dominant taxa. Control sites showed higher abundances of plant-associated and potentially pathogenic fungi, whereas Tiny Forests were characterized by saprotrophic taxa linked to organic matter turnover and nutrient mobilization. In addition, regional differences between Berlin and Frankfurt contributed to community composition, emphasizing the combined influence of vegetation, soil conditions, and local environmental context.These findings show that Tiny Forests harbor distinct fungal communities compared to adjacent control sites, with a shift toward saprotrophic taxa involved in decomposition and nutrient cycling. Our results indicate that Tiny Forests can alter urban soil fungal communities, though the strong site-specific variation highlights that local environmental conditions play an equally important role in shaping these communities.