Development phase convergence across scale in a primeval European beech (Fagus sylvatica L.) forest

Despite the recognized influence of spatial resolution on forest life cycle classification typologies, neither the effects of scale (i.e., extent) on development phase assignment nor the pathways of subplot convergence with increasing scale have been quantified. We applied an objective development phase classification protocol to subplots of a 10-ha primeval European beech (Fagus sylvatica L.) forest ranging from 156.25 m² to 10000 m² in extent. The assignment of one of the eight phases [Gap and Regeneration, Establishment, Early Optimum, Mid Optimum, Late Optimum, Terminal, Decay, and Multi-Sized (aka Plenter)] to each subplot was tallied at each scale and the pathways by which subplots in given phases at smaller scales were merged into larger subplots were summarized. As spatial scale increased, the most immature phases (Gap and Regeneration, Establishment, Early Optimum) converged into the mature phases (Terminal, Decay, Multi-Sized) and were no longer assigned by the 1250–2500 scale at which the mature phases dominated. As subplots assigned to one of the eight development phases at a given scale were merged with neighboring subplots to attain the next larger scale, many different possible pathways for convergence emerged but the number of observed combinations declined with increasing scale. Assignment to the most complex phase increased with increasing scale until ultimately all subplots were assigned to this phase. In addition to confirming the scale dependency of development phase assignment, these results support the hypothesis that the immature development phases are assigned predominantly at the smaller scales that correspond to the prevailing disturbance regime while mature phases are assigned predominantly at larger scales. We further observed a convergence with increasing scale on the most structurally complex phase. The convergence of immature phases on more mature phases with increasing scale likely reflects the dual dynamic of fast, short-term gap dynamics predominant at small scales and the slow, long-term dynamics of maturation, maintenance, and persistence that dominate at larger scales. The assignment of development phases at fine spatial resolutions, therefore, is necessary but not sufficient for a comprehensive investigation of the mosaic cycle. Further, examining development phase assignment across spatial scale may enable the identification of the spatial scale of predominant disturbances by investigating and comparing the rate at which phase transitions occur across scales in different primeval forests.