Structural Traits of Old-Growth Beech Forests in the Central Apennines (Italy)

Old-growth forests are recognized as key reference systems for biodiversity conservation and sustainable forest management, yet they remain rare and highly fragmented ecosystems across Europe. In this study, we developed and applied a quantitative, measurement-based framework to assess candidate old-growth beech stands by comparing their structural attributes with reference old-growth forests and with a broader set of beech forests from the National Forest Inventory (NFI). Specifically, we compared the structural attributes of two candidate old-growth (COG) beech stands to assess their degree of naturalness and their similarity to three reference old-growth (ROG) beech forests in the central Apennines. The approach integrated field-based structural measurements, deadwood quantification, dendrochronological assessment of dominant trees and diachronic aerial imagery evaluation, comparing COG stands with both ROG and other beech forests from the NFI database. The two COG stands differ clearly from common beech forests, exhibiting lower stem density, larger size variability, higher occurrence of large trees and of standing wood biomass. Stem diameter distributions followed a reverse J-shaped pattern, typical of uneven-aged and scarcely managed forests. Some very old trees were also found, especially at one of the two COG sites. These characteristics are largely comparable to the ROG beech forests, except for deadwood volumes, lower at the two COG forests. In addition, historical aerial imagery and tree-ring analysis suggested that these forests are intermediate stages along an old-growth gradient. Our findings demonstrate that a prolonged forest management abandonment of over 70 years can induce the development of old-growth attributes in Mediterranean mountain beech forests, even in stands previously coppiced or pastured for a long time. This study provides a replicable measurement-based approach for identifying and validating candidate old-growth forests, under current Italian regulations and contributes to conservation targets consistent with the EU Biodiversity Strategy for 2030.