The population structure of Carex dioica – a rare boggy species in Ukraine – has been studied for the first time. As a result, five types of spatial arrangement of C. dioica individuals, depending on their reproduction and living conditions, were established: scattered-diffuse, densely-diffuse, group, spotted and mosaic. Intensive vegetative propagation (often in the absence of seed reproduction) of individuals contributes to the group and spotted spatial structure of population. For low intensity of seed and vegetative reproduction, the arrangement of generative individuals turned out to be scattered-diffuse. Effective generative reproduction of a population was accompanied by a densely-diffuse distribution of individuals, and a combined type of reproduction (effective generative and vegetative) under favourable growth conditions contributes to its mosaic spatial structure.
Regardless of the growth conditions, all C. dioica populations were characterised by a left-hand age spectrum which was the result of an effective vegetative renovation of individuals and a stress-tolerant type of strategy of this species.
Under optimal growth conditions, the C. dioica populations were characterised by the prevalance of females compared to male ones (2:1), and under stress – a radical change in their sex ratio was observed towards a complete dominance of one of the genders. It was found that 50% of the studied C. dioica populations appeared to be thriving. Regardless of the vitality type of the population, the female individuals of this species, compared to male ones, realised their growth potential much better and, therefore, made a greater contribution to population vitality.
It has been established that species of the subgenus Psyllophora (Degl.) Peterm. (Carex L.) are characterized by very disjunctive areas and the limited regional distribution (Carex pauciflora Lightf. and C. rupestris All.), or are known from a few localities only (C. obtusata Liljebl.). Dioecious species of this subgenus (C. dioica L. and C. davalliana Smith), reach the eastern and southern limits of their distribution in Ukraine, where they are the most widespread. However, a big number of their localities have been already lost.