In 2017, the 90th anniversary of the senior lecturer of the Department of Geobotany and Plant Ecology of St. Petersburg State University, Honored Ecologist of the Russian Federation, Yu. N. Neshataev (1927- 2006) was celebrated. This paper contains a brief review of his researches, as well as the works of his colleagues and students of the Department of Geobotany and Plant Ecology on the study of the unique forests of the site "Forest on the Vorskla river" which is the part of the "Belogorye" reserve (Belgorod Region). For more than 50 years in this place Neshataev carried out researches on the structure, dynamics and functioning of forest communities. New approaches and a multilateral analysis of the structure and dynamics of oak forests in forest-steppe zone were realized in the works of his colleagues and pupils, who continued and developed his ideas. Preserve forest site "Forest on the Vorskla river" is located on the high right riverbank of the Vorskla and has a size about 1100 hectares. Natural forests occupy 55 % of its territory. The most valuable and close to native primary forests are fragments with forest of 300-year-old high oak. At present, the vegetation of the reserve is highly modified due to the intense digging activity of wild boars and the natural dying of old trees in the upper layer. The large-scale mapping of the vegetation of the reserve has a special place among the different fields of Neshataev's researches, because he considered this method as the main component of monitoring in protected areas (Neshataev, 1996). To obtain a set of comparable maps made every 10-15 years Neshataev has elaborated special "random-statistical method" (Neshataev, 1967, 1970, 1971). This method is based on regular placement (with 100 m steps) and precise linkage of the picket's network, and the plots for relevés are placed in accordance with it. The most interesting materials using this method were obtained in the "Forest on the Vorskla river", where the full vegetation mapping was carried out 3 times: 1961 (Neshataev, 1962, 1967), 1984-1985 (Neshataev et al., 1993) and 1996-1997 (Neshataev, Ukhacheva, 2001). A comparative analysis of the obtained results revealed a process of "mesophilisation" as a general trend of the vegetation dynamics in the forest-steppe zone. In the late 1950s the area of old high oak forests in the reserve was 160 hectares, but by the mid-1990s it decreased to 130 hectares, and in the rest of the territory the oak forests were replaced by linden and maple forests. At the same time, the "expansion" of Aegopodium podagraria has been observed, this species became increase in the role of more hygrophilous species and a decrease in participation of xerophytes have been marked in all communities of the reserve, including dry ecotopes with pine cultures and meadows of forest glades. The second trend revealed by maps comparison is the progressive decay of the upper layer of native primary oak forests: already in the 1990s, these oak forests in the reserve were typically overmatured stands. In addition to vegetation mapping, the dynamics and structure of old forest communities were studied in permanent plots (100×100 m) established in the 1930s by academician V. N. Sukachev. From 1966 to 1971, when the researches on International Biological Program were implemented in the reserve, a large number of new information was obtained in these permanent plots. In this period the following subjects were studied: productivity and seasonal dynamics of forest communities, the photosynthesis of woody and herbaceous plants and its dependence of the forest microclimate, and other aspects of the functioning of oak forest ecosystem. As a result, the highest biological productivity of oak forests in the forest-steppe zone was found, considerably exceeding other ecosystems of the temperate belt, as well as conditions determining a high level of biomass accumulation were revealed. Scientific studies by Neshataev were continued by the works of his colleagues and students of the Department of Geobotany and Plant Ecology. A list of some researches is given below. 1) Analysis of the formation of crown of linden during the ontogeny under conditions of forests with dominance of different tree species (oak, ash, linden, and birch). Characteristics of crown structure, which most accurately reflect the specific conditions of tree development within the phytocoenosis, were revealed. 2) Study of the stand structure in quasi-native forest communities based in the assessment of tree species coenopopulation condition. It was shown that the coenopopulation of Quercus robur is incomplete, because it does not include immature individuals. 3) Study of ecological fields of trees-edificators found that in the forest-steppe zone their influence on the herb layer is determined by the microclimate change creating by individual tree, whereas in the taiga zone the increase in soil richness under the crowns of broad-leaved species also has a significant effect. 4) Use of the Restriction Fragment Length Polymorphism (RFLP) method and testing of soil samples on nitrogenase activity allowed to obtain data on the bacterial community composition in soil under the crowns of lindens and beyond them. It was shown that Tilia cordata significantly affects the composition of the soil microbiota. 5) Study of the renewal of broad-leaved tree species in the oak forest, which showed that the amount of recruit-stock (young trees) is higher in the middle-aged forests than in mature and overmature forests. This is due to the fact that the formation of "windows" is absent in the old forests, where trees in the upper layer dies off over the decades, and during this time all gaps in the canopy are filled with the crowns of fast-growing sciophyte Acer platanoides. 6) Recruiting of broad-leaved tree species was also studied in the plantations of introduced trees (Quercus rubra, Robinia pseudoacacia, Phellodendron amurense etc.) and on forest glades. In particular, it has been found, that successful oak restocking is possible only in large glades (not less than 1 hectare). Linden, ash, maple and ulmus can successfully restore on smaller glades (from 0.1 to 1 hectare). 7) The ecological conditions of the formation of oak forest communities on the reserve territory in the historical time have been reconstructed. Three stages of this process were revealed: the middle of the 17th century (after of 'zaseks' organization for protection of forays of Cremean nomads), the end of the 19th century (in the places of clear cuttings), 1960-1970s (in the places of forest glades). Carried out on a unique object - protected 300-years old oak forest - the researches of the staff and students of the Department of Geobotany and Plant Ecology supplemented and detailled our knowledge about the dynamics of broad-leaved tree forests on one hand, and allow us to identify difficult problems of conservation of protected communities on the other.