Complex approach to the estimation the species composition of natural regrowth
Authors: Skliar V. G. 
Published: February 2018

Suggested complex approache to the assessment of the species younger generation of forest tree species, which is formed under the canopy of the parent stands, and in particular to the study representation in phytocenoses of various groups (cohorts) of plants. Researches, the results of which formed the basis of the published work, were conducted during the period from 2002 till 2014 on the territory of Livoberezhne Polissia. We have studied forest phytocenoses that belong to twenty four association groups of forest vegetation and which are typical for this region. The work has been accomplished with the use of geobotanical, population methods and with the use of mathematical and statistical processing of data. It was shown that for the disclosure laws of species composition formation it is appropriate to resume the use of certain methods of mathematical statistics, including the criterion x2. For a number of key fores-forming species of the region (Pinus sylvestris L., Populus tremula L., Acerplatanoides L., Tilia cordata Mill., Ulmus laevis Pall.) it was statistically proven that their young generation are drawn towards certain forest aggregations. Seed (fruit) dispersion features, peculiar to forest-forming species, intensity of their eurybiontic or stenobiontic properties and plant adaptative potential in general were shown to be one of the defining factors as for the species composition of regrowth. A method is proposed constructing a «cohort pyramids of natural regrowth», which allows you to visualize the basic features of the representation of different groups of young generation in forest phytocenoses of the given region. Pyramid stages, each matching a certain cohort, give information about the number of forest phytocenoses with the plants of one or another inner population group. It was shown that all basic variants of possible cohort division by phytocenoses quite fully represent four types of pyramids. Prevalence of cohorts of forest-forming species by phytocenoses can match not only four types of pyramids but their various combinations as well. Fluctuations of quantitative and qualitative indices of reproduction during years, as well as fluctuations of weather conditions and thereafter the change of degree of how favorable the conditions of place of growing are for the formation and development of young generation cohorts - all this can lead to the fact that pyramids acquire fragmented nature. The comparison of the actual cohort pyramids with the theoretical ones showed that there is a gradual decrease of young generation prevalence by association groups in P. sylvestris as in the line: small undergrowth → middle undergrowth → large undergrowth, as well as in the line: mature trees → young trees → large undergrowth. The decrease of cohort prevalence by association groups becomes apparent in Q. robur and P. tremula in the line: small undergrowth → middle undergrowth → large undergrowth → young trees, as well as in the line: mature trees → young trees. Cohorts of generative trees, not of the small undergrowth, are the most spread by association groups in P. sylvestris unlike Q. robur, B. pendula and P. tremula. In P. sylvestris, Q. robur, B. pendula, A. platanoides and P. tremula cohorts of big undergrowth or young trees of forest stand stage are the least represented in association groups. The lack of fragmented variants is the common feature of actual cohort pyramids P. sylvestris, Q. robur, B. pendula, A. platanoides and P. tremula.