The birth, growth, and death processes of natural European beech forests leave a structural signature of live biomass that fluctuates throughout the forest cycle, remaining low during the Gap/Regeneration and Establishment Phases, rising through the Optimum phases, and peaking in the Terminal phase before declining again in the Decay phase. Vertical stand structures are also postulated to vary across development phases, but in the opposite pattern to biomass—waning where biomass peaks. We tested this hypothesis at small scales aross a 10 ha old-growth European beech stand by applying an objective rule-based development phase classification protocol to assign development phases to small (156.25 m2) grid cells superimposed on the stem-mapped forest. Each cell was assigned to one of 8 development phases (Gap & Regeneration, Establishment, Early Optimum, Mid Optimum, Late Optimum, Terminal, Decay, and Plenter) on the basis of canopy projection area, maximum tree diameter, share of basal area in deadwood, mean tree diameter, and the normalized quartile difference in tree diameters. Permutation tests, corrected for multiple comparisons, were used to test for differences in structural metrics among development phases.
We show that even at this small scale biomass and volume, as well as indirect measures of live tree biomass, followed the expected pattern of increase through the early phases and peak in the Terminal phase before declining in the Decay phase. The distribution of live tree volume among canopy strata and the variation in tree diameters demonstrated the same pattern as biomass, while variation in tree heights, inequity in basal area, and the structural complexity index closely followed the biomass pattern. The pattern in forest structure reflects the shade tolerance of beech and the persistence of small diameter trees throughout the development cycle, including during periods of high biomass. On the one hand, vertical structure rises somewhat along with biomass at small scales. On the other, baseline levels of vertical structure appear to be relatively high at small scales. These findings indicate that European beech forests should lend themselves readily to management to optimize both commercial volume and vertical structure.