Temporal dynamics of propagule bank and established vegetation in three aging stormwater ponds: Pre- and...

Stormwater ponds have become essential tools for managing hydraulic functions and water quality in urban environments. Beyond their regulatory ecosystem services, these ponds also provide support for plant communities and serve as local biodiversity hotspots. This study examines the phytocenosis composition (propagule bank and established vegetation) in three urban stormwater ponds (P1, P2, and P3) after eight years of operation (2020) and following a dredging operation (2021) aimed at restoring their primary functions. The objectives were to: (1) analyze the phytocenosis composition, (2) assess the impact of dredging on the phytocenosis, and (3) propose management recommendations to address long-term vegetation challenges in stormwater ponds. Propagule bank studies identified 19 and 16 species in 2020 and 2021, respectively. Results revealed low similarity between propagule banks and established vegetation, consistent with literature findings, primarily due to the environmental filter of water level. No significant differences in propagule bank or established vegetation were observed before and after dredging. Although the 2021 propagule bank contained 2.3 to 5.4 times fewer propagules than in 2020, a similar diversity for P1 and P3 is calculated. Additionally, post-dredging, the evenness of the propagule bank improved, indicating a shift toward a more homogeneous composition over time. In 8-year-old ponds, propagule banks were dominated by 2-3 species, compared to 4-5 species in the 9-month-old bank. These findings demonstrate that dredging effectively restores hydraulic and sediment storage functions while enhancing the evenness of the phytocenosis without compromising propagule bank diversity. Thus, this maintenance operation does not undermine the biodiversity-supporting role of the ponds. Moreover, species established through natural colonization from surrounding environments contribute valuable ecological services, including regulation and biodiversity support, provided natural stands are available in the urban landscape.