Low understory condition in an oak forest in Hungary, 1972 and 2022 – Síkfőkút Project is 50 years old

: Serious oak decline was first detected in 1979-80 in a mixed sessile oak – Turkey oak forest ( Quercetum petraeae-cerridis Soó 1963). This decline resulted important structural changes in the understory shrub layer. Despite of this, relatively few studies deal with shrub communities and shrub layer dynamics after oak death. The goals of this research were to determine the conditions of low shrubs and analyse the possible changes in this layer after 5 decades from the beginning of Síkfőkút research. Specimens which were lower than 1.0 m in height were categorized as low shrubs in the shrub community. In 1972 and in 2022, 1617 native low shrub species were observed in the understory; 15 species were present continuously in the forest. The density of low shrubs was 87401 and 17317 specimen ha -1 . The most common low shrub species was Ligustrum vulgare and 5 decades later Quercus petraea with 24.1% and 37.8% ratio. The mean height and mean diameter of low shrub species changed among 10.3-67.0 cm and 1.5-7.5 mm. The mean cover of these shrubs fluctuated between 35 cm 2 and 2026 cm 2 based on the two measured year. Our results suggest that the low shrub layer responded negatively to the biotic and abiotic factors under 5 decades; this is especially true to the density, cover and diversity indices of species.