The impact of salvage logging on herb layer species composition and plant community recovery in Bialowie(z) over dota Forest

Bialowie(z) over dota Forest is one of the closest to pristine forest ecosystems in temperate vegetation zone in European Lowland, which is still being transformed by forest management. We investigated the effects of salvage logging of spruce stands killed by bark beetle on the recovery process and the biodiversity of the herb layer in the early stages of vegetation development after felling, on the habitat of mixed deciduous, oak-lime-hornbeam forest (Tilio-Carpinetum). We tested: (i) to what extent salvage logging modifies the plant species richness and diversity compared to sites left intact; (ii) whether clear-felling leads to an increase in diversity of vascular plants; and (iii) which ecological groups of plants benefit, and which are hindered by disturbance, depending on age and size of the clear-felled site. Salvage harvesting executed between 2012 and 2016 led to an increase in overall plant diversity. However, the winners were the species of open habitats, promoted by soil disturbance, whereas the number and cover of ancient forest indicator species decreased in comparison to unlogged forests. Both trends were significantly related to the increasing size of clear-felled sites, and developed right after logging. A comparison of the species composition of the disturbed (logged and unlogged) sites with undisturbed forest with stands unaffected by infestation, treated as control plots revealed the great potential of the affected sites for spontaneous recovery towards the oak-lime-hornbeam forest community, despite 50-90 years of spruce-dominated stand cover. We conclude that continuous deterioration of the forest habitats via clearcutting of stands affected by insect outbreak, followed by tree planting, substantially reduces the chances of successful, natural regeneration towards deciduous, structurally complex and diverse forests.