Deadwood occurrence and forest structure as indicators of old-growth forest conditions in Mediterranean mountainous ecosystems

In order to identify the distinctive traits of old-growth forests in a Mediterranean context, deadwood occurrence and forest stand structures were investigated in remote forests not subject to anthropogenic disturbance over the past few decades. Five study sites in south-central Italy were selected, and structural parameters were recorded in 1-ha plots. Living trees, deadwood, types, and decay stages were inventoried in the selected sites. Living tree volumes and amounts of deadwood indicated large variability among the investigated forest stands, ranging from 363 to 702 m3ha-1 for living trees and from 17 to 143 m3ha-1 for deadwood. Downed deadwood was the most abundant component, due to the natural mortality occurring in the stands. Stumps were the least common among the types of deadwood. All the decay classes were present in each study site. The main structural features useful for characterizing these old-growth forest stands included a multi-sized diameter distribution of living trees, the presence of small-scale gap dynamics, tree height heterogeneity, and high values of living volume and basal area. A ratio of dead to living wood not lower than 10%, downed deadwood much more abundant than standing deadwood, and a large range of deadwood size and decay classes across all the deadwood components are useful traits for tracking old-growth stages in these Mediterranean forests.