SUMMARY
There was elucidated the original approach to the evaluation of phytopopulation size structure. For its characteristics it was offered to use the special index - index diversity of size structure (?DSS). There are presented methods and algorithm of its determination. There was demonstrated that index diversity of size structure can be used at populational studies of species that belong to the different living forms. Especially phanerophytes (Pinus sylvestris) and hamephytes (Ledum palustre). As to Pinus sylvestris and Ledum palustre with help of index diversity of size structure was objectively proved that its cohorts and ontogenetic groups that growth in composition of forest phytocenoses typical for Ukrainian Polissya are not characterized with high level diversity of size structure. The value of index diversity of size structure is mainly less than 20 %. In phytopopulation the specific and phytocenotic peculiarity is demonstrated by diversity of size structure and also by representation of plants of certain size classes.
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