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

On June 14th, 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 15th and July 15th 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.2012年6月14日，笔者于一次温和风暴中见证一株胸高直径（diameter at breast height, DBH）达111 cm的欧洲山毛榉（Fagus sylvatica）倒伏，由此形成一处约400 m²的冠层间隙（canopy gap）。该冠层间隙位于意大利亚平宁山脉中部格兰萨索-拉加山国家公园（Gran Sasso and Monti della Laga National Park）内的Venacquaro溪右岸，海拔1240 m，地理坐标为42°30'00"N 13°30'40"E，此处为一片森林覆盖的山地山谷。 冠层间隙形成数日后，笔者设置了9个5 m×5 m的永久样方（quadrat），并于2012年至2024年连续13年每年开展1次复查；所有调查均定于6月15日至7月15日期间进行，以确保同时观测到春季与夏季物种。 其中3个样方设于冠层间隙内部，3个设于间隙边缘，剩余3个设于林内。冠层间隙内的3个样方分别位于间隙中心5 m处的三个主方位（南、北、西）；间隙边缘与林内样方则分别沿相同方位，设于距间隙中心25 m与45 m处，但存在一处例外：原计划设于冠层中心西侧25 m与45 m处的样方，改设于中心东侧25 m与45 m处，以避开一条林间步道。 在每个样方内，笔者按三个不同层次开展植被调查：乔木层（树高>3 m）、灌木层（1.3 m<树高≤3 m）以及地被层（树高≤1.3 m）。记录各物种的存在情况后，笔者采用有序盖度等级标尺进行目视盖度估测，等级限值依次为0.5%、1%、2%、5%、10%、15%、20%，后续每10%递增至100%。野外调查时分别针对各层次赋值盖度值，但统计分析时则以样方为单位进行汇总。 此外，每个样方内还记录了一系列微地形变量，并使用半球面冠层密度仪（hemispherical densiometer）沿四个主方位进行四次读数，以估测冠层开放度，作为林下层可获得光照的间接指标。