A yearly resolved time-series of vegetation change in a canopy Gap in the Venacquaro valley

On June 14^th, 2012, I witnessed the collapse of a large European beech (Fagus sylvatica) tree having a diameter at breast height (DBH) of 111 cm during a mild windstorm, and the consequent opening of a ca. 400 m² canopy gap. The canopy gap is located at 1240 m elevation on the right bank of the Venacquaro stream, a forested mountain valley in the Gran Sasso and Monti della Laga National Park (central Apennines, Italy) (42°30'00"N 13°30'40"E). A few days after the opening of the canopy gap I established nine permanent quadrats, 5 m x 5 m in size, which I resurveyed yearly for thirteen consecutive years (2012–2024), always in the period comprised between June 15^th and July 15^th to ensure both vernal and summer species were detected. Three quadrats were positioned inside the canopy gap, three at the gap margin and three in the forest interior. The three quadrats within the canopy gap were located at five meters from the gap centre in three cardinal directions (S, N, W). The margin and forest interior quadrats were located, respectively, at 25 m and 45 m from the gap centre, along the same directions, with one exception: the quadrats located 25 and 45 m West of the canopy centre were replaced by quadrats located 25 and 45 m East of the centre, to avoid a forest trail. In each quadrat, I sampled vegetation in three different layers: tree (height >3 m), shrub (1.3< height ≤3 m) and ground layer (height ≤1.3 m). After recording the presence of each species, I visually estimated their cover using an ordinal cover class scale with class limits 0.5%, 1%, 2%, 5%, 10%, 15%, 20%, and thereafter every 10% up to 100%. Cover values were assigned separately for each layer in the field but aggregated at quadrat level for statistical analysis. In each quadrat, I also recorded a set of micro-topographical variables, as well as four readings of a hemispherical densiometer directed in the cardinal directions to estimate the openness of the canopy, as an indirect measure of light available at the forest floor.