Latitudinal transformation of tugai forests in the Lower Amu Darya River reflects the degradation of floodplain vegetation

Tugai ecosystems, including poplar forests, are among the most threatened under conditions of global environmental change. Based on the analysis of 312 geobotanical descriptions representing the Tugai forests of the Lower Amu Darya River, the current state of vegetation was evaluated across four segments of the river valley. In the continental part of the river delta, there is an intensification of salinization processes and degradation of poplar communities. Due to the absence of hydraulic structures in the upper part of the study area, vegetation changes are minimal; here, valley ecosystems remain under natural floodplain conditions, and plant communities exhibit low levels of transformation. Vegetation in the two middle sections, located in areas with regulated water flow, shows significantly less degradation compared to the delta. However, a negative trend in the dynamics of Tugai forests is predicted for these areas, associated with the progressive aridization of the climate. The transformation is reflected in the floristic composition of the vegetation across different valley segments. The highest number of differentiating species is observed in the delta part of the Amu Darya River, which is explained by the formation of halophytic shrub and herbaceous communities, as well as ruderal assemblages of annual plants that replace forest communities. The southern section is characterized by a distinct species composition, where indigenous and long-persisting poplar forests dominate the valley complexes. An analysis of species constancy in Tugai communities indicates a consistent increase in vegetation heterogeneity toward the Amu Darya River delta.