Over 80 years without major disturbance, late-successional Bialowie(z) over dota woodlands exhibit complex dynamism, with coherent compositional shifts towards true old-growth conditions

Controversies about successional dynamics of woodland communities have a long history, dating back to the classical debates between Clements and Gleason and continuing into the present. These debates have largely concerned the predictability or convergence of forest developmental trends as well as the relative importance of different mechanisms and forces driving forest succession. However, opportunities for rigorous testing of competing hypotheses are limited, mainly because plot-based studies of forest vegetation spanning more than a decade are scarce and even fewer concern late-successional stands. We exploit a unique long-term dataset from mesic temperate forests of eastern Poland, spanning c. 80 years (1936-2012) in strictly protected, late-successional woodlands assigned to seven different 'structural types'. We use non-metric multidimensional scaling to assess the stability of species composition over the study period. We examine the predictability of composition and change trajectories over time using Mantel statistics, and we examine the changes in distributions of dissimilarity indices to assess convergence or divergence at the examined time and spatial scales. Tree communities in Bialowie(z) over dota Forest have changed substantially over the last eight decades. Several species (aspen, birch, pine, oak, ash, maple and spruce) exhibited large decreases in density, while a few other species (especially hornbeam and lime) have increased in importance across a wide range of initial compositional types. Forest types recognized in earlier periods have become much less distinguishable. Metrics do not yet show clear successional convergence, mainly due to (a) decline in the previously broadly distributed spruce and (b) persistence of large individuals of intermediate, long-lived species (even though these species lack significant regeneration). Synthesis. Late-successional woodland communities of Bialowie(z) over dota Forest are clearly dynamic and do not show quasi-equilibrial properties often assumed of old-growth forests. Forest types previously recognized as distinct have become progressively less differentiated. Plausible explanations invoke alteration in competitive relationships due to complex changes in environment, including warming climate, N deposition, natural and human disturbance, and ungulate herbivory over 80 years. Hornbeam and lime have been favoured over spruce, pine, oak and birch, although potential successional convergence is far from complete at this time. In the absence of major disturbance, we expect future decades to show continued successional homogenization.