The most commonly used old‐growth forest indicators are structural attributes; nevertheless, they do not necessarily represent the biodiversity value of old‐growth forests. The aim of this study is to analyse the relationships between species richness data of different taxa and structural indicators of old‐growth and to identify taxonomic/functional groups, species and structural attributes that may be used as indicators of old‐growth. To achieve this goal we sampled forest structure, vascular plants, lichens, bryophytes, fungi, saproxylic beetles and birds in mature and old‐growth stands in southern Italy. We calculated Spearman’s correlation coefficients between species richness data and structural attributes. Analyses of indicator species, co‐occurrences and two‐way clusters were performed on the multi‐taxonomic list. The group of vascular plants most significantly correlated with other groups in terms of species richness; furthermore, it displays the highest proportion of between‐group co‐occurrences. The resulting multi‐taxonomic list of potential indicators may serve as an effective means of detecting and monitoring forest ecosystems; however, for this goal, structure‐based indicators, such as forest structural attributes and vascular plant species composition, are of primary importance.

This study is focused on the selection of variables affecting lichen and bryophyte diversity in Mediterranean deciduous forests. Plots representing two forest types (Fagus sylvatica and Quercus cerris forests) and two forest continuity categories (old‐growth (OG) and non‐OG forests) were selected in the Cilento and Vallo di Diano National Park (Italy). The presence and the abundance of bryophytes and epiphytic lichens were recorded. Structural variables of the forests and vascular plant species richness have been used as predictors. A strong positive correspondence between the two groups of organisms was found. Higher species richness and the distribution of rare species are related to OG stands, while a qualitative (species composition) rather than a quantitative (species richness) difference between the two forest types was observed. Some species elsewhere considered as indicators of forest continuity, such as Lobaria pulmonaria, Antitrichia curtipendula, and Homalothecium sericeum, are associated with OG forests, independently from forest type, suggesting that they can be regarded as suitable indicators also in Mediterranean forests. Finally, our results suggest that old trees, high levels of basal area, a broad range of diameter classes, and high understory diversity are the main structural features affecting cryptogamic communities, while no correlation was found with the occurrence of deadwood.