Abstract
Pasture ecosystems provide essential ecosystem services, yet poisonous plants create persistent veterinary and economic risks. We examined how hydroclimatic variability restructures the poisonous-plant assemblage across three Central Kazakhstan rangelands during an extremely dry year (2023) and an exceptionally wet year (2024). A total of 32 toxic vascular plant species were recorded. Xeromorphic pastures maintained a stable floristic core across years, whereas the wet year triggered recruitment of wet-associated poisonous taxa (hydrophytic/hygrophytic group) exclusively in the Nura River floodplain and increased species richness. Thus, interannual variability was controlled by hydrologically sensitive habitats rather than wholesale community turnover. The principal grazing hazard was associated with flood-related species (e.g., Cicuta virosa, Oenanthe aquatica) and persistent forage contaminants (Datura/Hyoscyamus, Lolium temulentum). These findings indicate that toxic-plant risk follows an asymmetric seasonal pattern: episodic post-flood hazard in floodplains combined with constant background risk in steppe pastures. Therefore, grazing management should integrate event-based monitoring of wet habitats with continuous forage-quality control.