Fresh water lakes are good objects for studying local flora, ecology and the distribution of lake plants. The data about the species pattern of the lake flora were collected. During summer biological practics and expeditions of Moscow Gymnasium on Southwest, which took place in the Thupa region, at Tchupa gulf of the White Sea, and in Udomelsky region, of Tverskaya province, near the lake Moldino, since 1999 till 2001. 17 lakes of the Tchupa gulf environ and 4 lakes of Tverskaya province were studied. The last ones were taking for the comparison, as a so-called "external group". The following parameters were noted for each lake: The length, width, depth, character of the bank, bottom, distance to the nearest road and to the nearest inhabited locality. A 7-degree scale was used for the study of the lakes, which allows to estimate the species pattern of the plants, but also their abundance on this certain locality. Any rooted sprigs were accounted. Therefore, many plants, forming a curtain, connected with subterranean sprigs, were accounted as several individuals, but terrene dendritic shrubs as one. One individual or several individuals situated closely. We designed a method of studying selected blocks for the description of flora. We have chosen a typical 20-meter length part of the bank (sometimes we increase the length of this sector). We noted all species of the banks growth in the borders of this sector. In case of the absence of prominent bank growth, we noted al species in the limit of 1 meter from the waterfront. Also we noted all new species of water plants available with our methods of studying. Our goal wasn't to make a thorough study of certain lakes, but to study a maximum number of lakes using simple methods. We tried to study all available lakes, but firstly the lakes that were situated closer to roads. We have to note that the names of many lakes studied in our work are named by our study group, because there was no full data on the maps. The data were processed by the computer statistic program Medium-R (package). Cluster data analysis 1999/2000 were preformed in such a way, that the lakes were divided into groups by their similarity, plant species and the plant species abundance. We used the Word method and the Manhattan metric. The dendrogram shows the lake classification by the flora composition.
In all situations the Tverskaya region lakes stand alone, which was predictable. It can bee observed, that the lake situated close to each other are very similar in their floral composition, for instance, Kolkovoe and Sfagnovoe, Luzha and Kishka, Levoe and Pravoe. After the removal from the statistics of the artificial lakes with very poor flora (Bezdonnoe and Klassnoe) we see a very clear cluster of sphagnum lakes, surrounded by the typical oligotrphic marsh (Levoe, Pravoe, Luzha, Kishka, Kamennoe, Kolkovoe, Sfagnovoe.)
Then we shortened the plant species list, leaving only the species that can be found both on the Karelian and Tverskaya lakes. After processing the data with the Word method, the Tverskaya cluster was still very clear, from which we can conclude that the lakes of these regions differ not only in plant species of the banks, but also in their abundance. This conclusion confirms the thesis of interzonal lake flora (Raspopov, 1985).
In 2001 we studied more than 20 lakes in the vicinity of the Tchupa gulf. Based on the same classification methods, all the lakes studied in 2001 fit in with the said above results.
Therefore: a) The statistic methods that we used allow us to receive an adequate lake classification, the received data are explainable; b) The lakes of the Tverskaya region clearly differ from the Karelian lakes in all data processing methods; c) The interlocation of the lakes determines their similarity; d) unique plant species have a weak effect on the difference of the lakes of different regions.
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