Long-term effects of gap creation and liming on understory vegetation with a focus on tree regeneration in a European beech (Fagus sylvatica L.) forest

The long-term effects of gap creation and liming on tree regeneration and understory competition were examined in a mature European beech (Fagus sylvatica) stand on a nutrient-poor site. In 1989, trees were felled to create four 30 m wide circular gaps, and 3 t ha-1 fine dolomite was applied to two of these gaps and the surrounding area, whereas the remaining two gaps and most parts of the stand remained untreated. In 2010, the stand density was 153 trees x ha-1 and the basal area was 29.51 m2 x ha-1. Testing a factorial combination of two levels of canopy cover (gap and stand) and two levels of lime application (limed and unlimed), the results of the case study partly support our initial hypothesis that the combined or single effects of liming and canopy removal on understory plant communities last for more than 20 years. Some effects disappeared slowly over time, while others did not. Understory vegetation of the unlimed gaps and thelimed and unlimed stands was rapidly dominated by beech regeneration, whereas limed gaps were dominated by fireweed (Epilobium angustifolium), bramble (Rubus fruticosus agg.) and raspberry (Rubus ideaus) for around 14 years. There, the density of the beech regeneration was reduced by competitive ground vegetation species. Plant species richness (n/100 m²) was still significantly different after 23 years, with an average 10 species per 100 m² in the limed stand area, 5 species in the unlimed stand area, 25 species in the limed gaps, and only 5 species in the unlimed gaps. Only the combination of liming and canopy removal enhanced the species richness in the long run. On our study site, this combination of liming and canopy opening had a long lasting influence on the ground vegetation in terms of retarding the beech regeneration and enhancing species’ richness.