The article is dedicated to soil and archaeological investigations of hill forts located in the southern part of the Central Russian Upland forest-steppes, which made it possible to identify directions and stages of the Late Holocene evolution of plant cover within river valley parts of watersheds. Two types of hill forts were studied: those referring to the same historical epoch (Scythian and Saltov-Mayatsk ones) and those having many layers. Paleoecological reconstructions have been carried out on the basis of comparative analysis of modern and ancient soils, buried under the defensive ramparts of the hill forts. In Scythian time, the watersheds adjacent to river valleys were open grasslands surrounded by forest vegetation. In the second half of the 1st millennium BC, these watershed lands were fully occupied by forests, which had displaced the steppe. The oscillatory nature of climate change in the Late Holocene influenced the spatial-temporal dynamics of vegetation and soil fertility. At the beginning of the Holocene Sub-Atlantic period 2800–2500 years ago, climate moistening favoured the expansion of woods along the slopes of river valleys and gorges to watersheds. Subsequent climate aridization (2500–1700 years ago) stopped this process. A new stage of watershed covering with forests started no earlier than 1700 years ago – after new climate moistening. Episodes of climate aridization and steppe areas expansion in the Late Holocene favoured soil fertility growth in the territory of hill forts and around them. The expansion of woods related to climate moistening decreased soil fertility and negatively influenced grain farming capabilities.