The 110-hectare Lébény Oak Forest is one of the last natural forest blocks in the Little Plain, where the invasion of black locusts and tree of heaven is threatening the naturalness of the stands. Two different methods were used to illustrate this: 1. a coarse-scale, forest plot-based survey using forest plot data; 2. a fine-scale survey based on field data collected in sample plots, which were divided into 25×25 m areas gridded with net. The first method can be used to get a sense of the dispersal dynamics of the two tree species, while the second method can be used to focus attention on propagule sources. The more recent black locust and tree of heaven distribution data collected during the finer-scale survey can provide important information on where and how to intervene with targeted conservation treatments to restore the natural state of the Lébény Oak Forest as effectively as possible by reducing the dispersion of the two species. From the analysis of the data recorded in the six baseline dates of the management plans, it can be concluded that black locusts have shifted from seed-based restoration to sprout-based germination restoration for both management types (cooperative farming, then national park management and forestry). In the forest planning period immediately before the regime change, the occupation of this species was 15.6 %, but in 2024 it is only 2.7 %. The presence of tree of heaven in forestry-managed forest areas was already recorded in the 1968 forest plan, but in a negligible proportion (1.5%). Although the proportion of this species stagnated between 2006 and 2024 (1.9% on average), its presence is permanent and two propagule sources are also visible in the area. Forest management and conservation interests are the same here, but attempts to eradicate tree of heaven have been unsuccessful. According to the results of the field sample survey, black locust was found in 82.3% of the 1640 relevés surveyed, while tree of heaven was found in 41.0%. Compared to the black locust, the distribution of tree of heaven per sample area is almost inversely distributed, paradoxically, interventions to control this species create favourable conditions for its occurrence. In addition to abundance, the diameter distribution of these trees is also an important issue. The estimated mean diameter distribution for black locusts reflects a near-normal distribution. For black locust, the diameter distribution per relevé is in line with the management of this species, but black locust specimens thinner than 5 cm were present in 8.0% of the relevés surveyed, clearly reflecting the invasive character of the species. In contrast, the highest frequency of tree of heaven was observed in the category "thin tree of heaven" being less than 5 cm.