Conservation Management Practices for Biodiversity Preservation in Urban Informal Green Spaces: Lessons from Central European City

Urban informal green spaces (IGS) represent valuable reservoirs of biodiversity within urban areas and are increasingly recognized as integral components of green infrastructure. They are perceived as temporary ecosystems, and the management of their vegetation is relatively understudied. The development time of spontaneous vegetation on transformed lands is considered to be in the range of decades, which makes it even more necessary to provide managers with better guidelines for such a long period. Two suggested management approaches for these areas involve: (1) retaining vegetation at various stages of succession (non-forest IGS) and (2) protecting advanced developmental stages (forest IGS), with options for balanced intervention or complete non-intervention. However, the differences in biodiversity between these two types in cities across Central Europe remain unknown, as well as whether the predictors of biodiversity at both local and landscape scales are consistent for non-forest and forest IGS. We examined factors such as habitat continuity, landscape structure, soil quality, and human impact to shed light on pathways for enhancing urban floristic diversity. Conducting extensive botanical surveys in existing informal green spaces (IGS) in Warsaw, we derived various parameters, including the total number of species, Shannon-Wiener biodiversity index, hemeroby, urbanity, share of species from distinct ecological groups, and the number of rare and ancient forest plant species. Tracing habitat continuity from the early 20th century using digitized aerial imagery provided a unique long-term perspective on IGS development. We revealed that no management is pivotal for the conservation of select rare and ancient forest species. On the other hand, partial abandonment with occasional maintenance may enrich species diversity across different successional phases. We uncovered the significant influence of landscape structure and human activity on vegetation species composition within IGS. Notably, IGS proximate to extensive forest landscapes displayed a marked abundance of forest species, alongside a greater prevalence of rare species. However, the presence of other vegetation types in the vicinity did not yield similar effects. Our findings indicate that IGS, when left untouched for decades near forested areas, are valuable for urban biodiversity. As cities across the globe seek sustainable paths, this research underscores the importance of properly understanding and integrating IGS into urban ecological planning.