Development phase delineation in primeval European beech using the dominant biomass strata protocol

Abstract

Reliable characterizations of developmental condition can help elucidate disturbance regimes, characterize structural development, and identify and describe old-growth. However, current forest life cycle development phase classifications are based on inconsistent, incompatible, or unreliable a priori archetypal structures that fail to capture the natural dynamics of old-growth European beech (Fagus sylvatica L.) forests subject to a small-scale disturbance regime. We demonstrate an alternative protocol for capturing phases of biomass upgrade based solely on the proportion of live-tree volume in seven progressive tree size classes, with an optional deadwood-share cut-off (30%) to also identify deadwood-rich patches when desired. The proportions of a 10-ha primeval European beech forest in the Ukraine assigned in 156.25 m2 grid cells to each of the Dominant Biomass Strata phases were in keeping with previously reported estimates. Amid a matrix (>60%) of Overstory, Upper Overstory, and Emergent phases, roughly a tenth of the area was classified to the early Open/Seedling and Understory phases, the Lower and Upper Midstory phases, and the Lower Overstory phase, respectively. Further, 12% of grid cells—across all phases—were deadwood-rich. The biomass proxies of live volume, basal area, and mean tree size increased distinctly with each subsequent phase, and were lower in the deadwood-rich category, in accordance with the forest life cycle. Structural complexity proxies varied inversely with biomass when defined as the distribution of volume among canopy layers, but similarly to biomass when defined using metrics based on tree size differences. High volumes of large-diameter deadwood were observed in all phases, consistent with previous observations of acyclic transitions following mortality. In pure primeval European beech, the synchronous pattern of biomass and size-based structural complexity metrics (including the standard deviation of tree diameters, the Gini coefficient for basal area, the diameter differentiation index T, and the structural complexity index SCI) may provide a natural model for the simultaneous optimization of volume and small-scale complexity in managed forests. With local adaptation, the proposed Dominant Biomass Strata classification protocol could be applicable to any site or forest type and used to classify stand development phases in young forests following stand-initiation or to classify patch development phases in old-growth forests subject to maintenance dynamics.