Restoring the Herb Layer of a Thermophilous Oak Forest: Effects of Shrub Removal and Grazing (S Poland)

Thermophilous oak forests are among the most species-rich forest ecosystems of central Europe and a relic of its traditional biocultural landscape. In the absence of grazing, they turned gradually into shaded, mesophilous oak-hornbeam forests. We tested three restoration treatments—annual shrub removal, supervised sheep grazing, and their combination—against a thinned-only control, on twelve 20 × 20 m2 plots in a Potentillo albae-Quercetum stand in S Poland, surveyed on 50 randomly placed 1 m2 subplots per plot in 2016 and again in 2019. Herb layer composition changed significantly in every variant, including the control. The variance explained by the survey year rose from 2.2% under thinning alone to 5.8% under removal with grazing. At the plot level, the herb layer became more light-demanding and less nutrient- and moisture-demanding, and the frequency of disturbance-tolerant species rose. Differences between the four variants were not statistically resolvable with three replicates each. Both grazed variants converged on the target community markedly more strongly than shrub removal alone and an order of magnitude more than the control, with grazing the component associated with the largest change. The characteristic species gained frequency, indicating that the treatments released formerly suppressed resident herbs rather than recruiting new colonists.