The dynamics of systematic structure floral complexes on the old fields during secondary succession

Abstract

The national plan of actions concerning the natural environmental protection in Ukraine in 2011–2015 presupposes the average reduce of the arable lands by 5–10 % with the help of withdrawal from the intense farming, preserving of the degradation and inefficient agriculture lands, with a purpose of the natural carcass elements extension (forests, meadows, pastures) and the rationalization of the agro-landscapes structure. It is known that the fitocenoses play a deciding role in the system of environmental preservation actions, its upgrade and improvement. According to the data of the Department of State Land Cadastre of State Land Agency of Ukraine of 01.01.2013 277.2 thousands hectares of land were excluded from the category of arable land and transferred to the old field land class consisting 0,5 % of the general area of Ukraine that is transforming under the influence of natural and anthropogenic processes. These changes in the structure and dynamics of the main landscape parameters and the danger of losing a significant part of biodiversity determine the relevance of the investigating systematic structure of the old-field species-composition at different stages of secondary succession. The research was made in 2010–2013 with the help of route and stationary methods on the calculation ground: 2×2 m for the grassy vegetation, 10×10 m for the tree and bush vegetation. The plots were chosen on different stages of the secondary succession, which most fully reflect the representatives of the flora complexes and enclose the whole spectrum of the main abiotic factors of its forming: I – old-fields, which were not processed for 1–3 years, II – old-fields, which were not processed for 4–7 years, III – old-fields, which were not processed for 8–13 years, IV – old-fields, which were not processed for 14–22 years. Taxonomic composition is given according to the field studies and basing on the collected herbarium material. Systematic spectrum (leading, middle and final) was defined using an average index of saturation (H) of higher rank taxa with lower rank taxa. To the middle part there belonged the amount of lower rank taxa equal to the average index of saturation of higher rank taxa ± 50 % of its value: H ± 0.5 × H. To compare the degree of species composition similarity there was used the Jaccard similarity coefficient (Kj). The similarity degree of floral complexes according to the systematic structure was defined using modified Bravais-Pearson coefficient of correlation (r). Taxonomic composition of the old-field land floral complexes of Prydnistrovske Podillia showed that it numbered 413 species belonging to 238 genera and 64 families. The old field floral complexes of the studied territory are characterized by the dominance by the amount of species and genera of few families, the taxonomic spectrum of which comprises 264 species (63,9 %) and 150 genera (62,9 %). In the genera spectrum of floral complexes prevails monotype fraction – 204 genera (85,7 %) uniting 253 species (61,3 %). The role of absolute indices of the floristic abundance (amount of species, kinships and families) have a natural tendency to extension, which is a result of the change in soil and climatic as well as the cenotic conditions in the process of demutation of the flora cover in the old-fields. The analysis of the floral wealth, systematic diversity and taxonomic composition indicate the dynamic process of flora-genesis at the old field lands and the largest similarity of floras of the 3rd and the 4th degrees of secondary succession as a result of stabilization of ecological conditions. The least similar are the floral complexes of the 1st and the 4th degrees of syngenesis. Besides the general systematic structure of the flora complexes of the old-fields, the determination of the species abundance of the biotopic old-plough lands still remains urgent. Based on the principles of the heterogeneity and change of the vegetation depending on the dynamics indices of the environment, dimensionally (discretely), as well as timely (successively) on the territory of the research, we found out and described the species abundance of 10 biotypes. The analysis of biotopes species composition similarity shows that most of them are characterized by low degree similarity. Our further researches will be connected with the peculiarities of the ecological succession at old field lands. The ecological analysis of floral complexes was based on the study of O. L. Belgard about ecomorphs.