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First signs of old-growth structure and composition of an oak forest after four decades of abandonment

Abstract The lack of natural references of dry-mesic oak forests creates conceptual obstacles for their conservation and close-to-nature management in Central Europe. Single-tree inventory was used to investigate stand characteristics and old-growth attributes of a Quercus petraea (Matt.) Liebl. and Q. cerris L. dominated, 120-year-old stand in a Hungarian forest reserve, abandoned approximately 40 years ago. All individuals were recorded with diameter ≥ 5 cm on the 3 ha study site. Logs, stumps, saplings and seedlings were also surveyed. 582 woody stem/ha belonging to 14 species were measured with single-tree inventory. Basal area values showed the total dominance of oaks in the canopy layer (99%) as a legacy of the long-term human exploitation. In contrast, young individuals of oak species were almost missing, and Acer campestre L. dominated the lower layers, indicating the transitional nature of the stand. Diameter classes showed a marked bimodal distribution. Both the abandonment of the reserve and the precedent severe oak decline contributed to the relatively high amount of dead wood (46 m3/ha). Four decades of abandonment is rather short time interval to generate a diverse forest composition and structure in a mature dry-mesic oak forest. The dense regeneration and shrub layer and the upsurgence of admixing species indicate the shift towards the uneven-aged and compositionally more diverse old-growth oak forest state. Among the structural forest features the dead wood had similar values as old-growth forests. If the recent trend continues, the studied oak forest develops towards a mixed forest with significantly lower ratio of oak species.