Biology session

Semi-natural forests in Hungary have become significantly more homogeneous in structure and tree composition over the past centuries as a result of the rotation forestry practices. The increase in structural heterogeneity occurs spontaneously and slowly with the gradual cessation of continuous cover forestry management, but can be also accelerated by conservation actions. In my research, I have investigated the growth and development of seedlings of the stand-forming sessile oak (Quercus petraea) and two mixed species, field maple (Acer campestre) and service tree (Sorbus domestica), under different canopy closures: artificially created gaps for conservation purposes and control in closed stands. The sample plots were located in the areas of the Bükk National Park Directorate, which consist of Pannonian-Balkanic Turkey oak–sessile oak stands. The same number of seedlings of the tested tree species were planted in the fenced sample plots (120 per species), and 120 oak and 87 maple seedlings spontaneously present were also selected. The height and diameter of these seedlings were measured regularly over the years between 2018 - 2023. Canopy openness values were determined using a spherical densiometer.

The results show that the increment in seedlings’ height differs significantly between the gap and control plots. In the gap areas, the highest growth was observed in service tree, maple showed medium growth and oak showed weaker growth. The growth of the seedlings suggests that any deficit in canopy closure affects their development, but the amount of light is not linearly correlated with the seedlings’ growth. With a high closure deficit, the seedling growth rate is lower due to the presumed competition with the undergrowth due to the higher light.

These results have shown that regeneration can be initiated by the creation of patches in homogeneous, closed-structured forests, but the issue of competition with undergrowth needs to be carefully considered when opening the gap. The increased light benefits mixed tree species more than sessile oak seedlings, and therefore these interventions can increase the future diversity of the tree population.