In the cuesta landscape, the natural forest vegetation is affected by the clear gradients in parent material. Most forests belong to the alliances Fagion sylvaticae, Luzulo-Fagion and Carpinion betuli. Forest associations show a clear shift in species composition from calcareous to acidic soils. The species-rich Carici-Fagetum and Hordelymo-Fagetum occur on steep slopes on Muschelkalk, with shallow Leptosols and Leptic Regosols, and pH values around 7. Galio-Carpinetum, with many wet-tolerant species, occurs on gentle slopes in Keuper marl, with Luvic Stagnosols and Planosols, pH around 5-6, and perched water tables during part of the year. The relatively species-poor Galio odorati-Fagetum is found on acidic loamy soils, such as the marls of the upper cuesta, Pleistocene river terraces and Loess deposits. Soil types range from Colluvic Regosols to Luvic Stagnosols, with pH values around 4. The species-poor Luzulo-Fagetum is found on plateau and upper cuesta of the Luxembourg sandstone, but also on the oldest river terraces. Soil types range from (Leptic) Arenosols and Podzols to Alic Stagnosols, and pH values are around or below 4. In forests plots on Keuper and Muschelkalk with base-rich, loamy topsoils, parent material was more important to species composition than litter quality. Calcicole species predominated on Muschelkalk, and wet-tolerant species on Keuper, although diversity was lower under beech than under hornbeam. The clear decrease in plant species richness from calcareous to acidic soil is discussed in terms of toxicity, nutrient availability and tolerance to wet conditions, but also in relation to landscape history and regional species pool.