Biologichni Studii / Studia Biologica

Background. The destruction of the Kakhovka Dam during Russia’s invasion of Ukraine triggered one of the most severe environmental disasters in Eastern Europe in recent decades. The abrupt draining of the reservoir eliminated essential aquatic habitats, resulting in a collapse of aquatic biodiversity, significant disruption of hydrological cycles, and widespread contamination. The subsequent colonization of the exposed flats, predominantly by two tree species, fails to compensate for the lost diversity of the former aquatic ecosystem. While the abrupt drainage resulted in the degradation of aquatic habitats and posed long-term public health risks, the newly exposed terrest­rial substrates have also facilitated spontaneous ecological succession. The most prominent colonisers of the dried-out bottom are hybrid willows (Salix × rubens) and black poplars (Populus nigra), which have rapidly formed dense pioneer stands. These emergent ecosystems now play a critical role in carbon sequestration, soil stabilisation, and microclimate regulation. Understanding the dynamics and ecosystem services of these formations is essential for developing sustainable restoration strategies for the post-war landscape.
Materials and Methods. Field surveys were conducted in April 2025 on the exposed bed of the former Kakhovka Reservoir, near Khortytsia Island. A total of 158 plots were evaluated in terms of tree presence, morphometric parameters, and environmental conditions. The height and diameter of Salix × rubens and Populus nigra trees were measured, and their biomass was estimated using geometric models. Soil pH, temperature, moisture and electrical conductivity were recorded at each plot. Ecological niche parame­ters were calculated using generalised additive models (GAMs). The carbon sequestration potential was estimated based on total biomass and converted into a monetary value using EU ETS carbon pricing.
Results and Discussion. Salix × rubens and Populus nigra exhibited high colonization rates on the exposed reservoir bed, establishing pioneer stands that exhibited distinct spatial patterns. Salix × rubens dominated moist, concave microsites, whereas Populus nigra was found on elevated, drier areas. Analysis of generalized additive models indicated that stands of Salix × rubens develop on soils with moderately acidic to near-neutral pH (optimum ≈ 7.25; tolerance range 6.43–8.03), elevated moisture (optimum ≈ 10.42 %), warmer temperatures (optimum ≈ 17.82 °C), and moderate electrical conductivity (optimum ≈ 0.38 dS m^–¹), whereas Populus nigra exhibits broader ecological plasticity: pH optimum ≈ 7.12 (tolerance 3.83–7.67), lower moisture (≈ 5.98 %), cooler conditions (≈ 12.80 °C), and low electrical conductivity (≈ 0.03 dS m^–¹). The species exhibi­ted significant differences in ecological tolerance and biomass accumulation. Allometric models revealed distinct growth strategies, with P. nigra developing thicker stems. The maximum carbon sequestration potential was observed at intermediate stand densities, with P. nigra providing a greater economic value per hectare. These findings emphasise the ecological significance of spontaneous afforestation and advocate for nature-based restoration methods over the technical reconstruction of reservoirs.
Conclusion. The spontaneous afforestation of the former Kakhovka Reservoir bottom by Salix × rubens and Populus nigra demonstrates the strong regenerative capacity of floodplain ecosystems. These pioneer stands provide essential ecosystem services, including carbon sequestration, soil stabilization, and habitat provision. Species-specific ecological preferences and growth patterns determine their spatial distribution and carbon offset potential. The estimated economic value of early-stage carbon capture is considerable, particularly for P. nigra. These findings support the conservation of emergent willow-poplar communities and emphasize the importance of integrating nature-based solutions into post-war landscape planning instead of pursuing technical restoration of the destroyed reservoir infrastructure.