Old-growth attributes in a network of Apennines (Italy) beech forests: Disentangling the role of past human interferences and biogeoclimate

In a network of six old-growth and three managed beech forests, distributed over a wide altitudinal range in the Central Apennines, we used principal component analysis to analyse a set of 15 commonly used structural and chronological indicators of old-growthness, related to both live trees and deadwood. Our goals were to (1) quantify the effectiveness of such indicators for ranking forests according to their degree of old-growthness and (2) disentangle the effects of site-related (e. g. elevation) and human-related (e. g. past management) factors on their variation. We selected eight indicators as best descriptors of forest old-growthness: mean age of the five oldest trees; snag volume; coarse woody debris (CWD) volume; density of medium-size snags [diameter at breast height (DBH) >= 47.5 cm]; forest stature; basal area; established regeneration and density of large trees (DBH >= 67.5 cm). We analysed their relative importance in informing us about the degree of old-growthness in our forests. Our findings suggest that several old-growthness indicators are to be considered carefully, because they are strongly linked to site conditions and particularly to the biogeoclimatic context. Moreover, we provide evidence for how past management can produce negative effects on some indicators.