Many species of disturbance-tolerant and invasive plants appear in the clearcuts and their populations persist for many years

One of the research topics of the Pilis Forestry Systems Experiment is to investigate the effects of different silvicultural practices on understorey vegetation in an oak–hornbeam forest stand. In the experiment, interventions of two significantly different forest management modes were studied between 2014 and 2020. Three interventions modelled the conditions of the so-called clear-cut forest management applied in the largest area of Hungary: a cut area, a group of residual trees in the cut area, and a so-called cut stand where half of the trees were removed. In Hungary, the continuous cover forestry method is still only applied in a small area, one of the most important elements of it is the creation of a gap in the closed canopy by cutting a few trees. The continuous cover forestry mode was therefore modelled with gap cutting. In addition to the above interventions, the experiment also included a control area where no interventions were made. The effects of the five intervention types were observed in 6 replicates (blocks).
We studied how understorey attributes change in response to different forest management and how these responses change over time. Then we assessed the ability of treatments to maintain the forest character of the vegetation. One of the most important differences between the experimental sites was the behaviour of disturbance-tolerant and invasive species. The majority of indicator species associated with the cut areas were disturbance tolerant (Cirsium arvense, Calamagrostis epigeios) and invasive, light-demanding species (Erigeron annuus, Conyza canadensis, Solidago gigantea). None of these species were present in the area before the interventions. The disturbance-tolerant bushgrass (Calamagrostis epigeios) and the invasive giant goldenrod (Solidago gigantea) started to become more common in the areas after the third year of the interventions (2017). The goldenrod was dominant in only a few areas, but was still present in some areas six years after the interventions (2020). The average cover of bushgrass was 9% five years after the intervention and reached 25-50% in some of the cuttings. None of these species were present in the plots, and if some individuals appeared in one year, they disappeared the following year. Compared to the cuttings, the soil moisture and humidity were higher in the cuttings. These microclimatic factors were probably behind the phenomenon that the experimental stands retained the forest understory character better because they proved more resistant to disturbance and invasive species than the cuttings.
The study shows that areas managed under continuous cover forestry methods can be more resistant to disturbance-tolerant and invasive species than areas under clear-cut management, and that increasing the proportion of continuous cover forestry management in our country is important from both ecological and conservation perspectives.