The dynamics of structure across scale in a primaeval European beech stand

Abstract

We explored the spatial dynamics of structural complexity in the living tree stratum in a 10-ha stem-mapped portion of an unmanaged nearly monospecific primaeval European beech (Fagus sylvatica L.) stand in Western Ukraine. Development dynamics were assessed through patterns of change in association across scales (from 156.25 m 2 to 1 ha) among stand basal area (BA), tree density, average and standard deviation (STD) of tree diameters, Gini coefficient (GC), the indexof spatial aggregation (R), diameter differentiation index (T) and structural complexity index (SCI). At the smallest scales, STD, GC and Tcontrasted patches of differing structure (i.e. large between-patchstructuraldifferences).Assubplotareaincreasedandincorporatedmoreheterogeneity,structural differences between subplots became more subtle and measures of tree-to-tree size variation (STD, T) lost sensitivitywhereasitwasgainedformeasuresofoverallwithin-patchheterogeneity(GC).Atsmallscales,differencesin STDlargelyexplainedvariationintheSCI(between-plotvariability);atintermediatescales,sizedifferencesamong neighbours(T)explainedmostofthevariability;andatlargescales,plot-leveldifferencesinBAanditsallocationto trees of different sizes (GC; within-plot variability) overrode size differences among nearest neighbours. The characterization of a fine-scale shifting mosaic of patches in different development stages appears to hold for primaeval beech forests in this spatially contiguous area of relatively large extent. The coalescence of small-scale processes into neighbourhoods, and then into patches at larger scales, may be best captured by the change in associations among structural measures across scales because the structural imprint of gap dynamics extends considerably beyond the scale of individual gaps.