Structural changes in the shrub layer were analysed in a Hungarian oak forest after the oak decline pandemics. This paper focuses on the following questions: (1) which of the woody species tolerated better the forest conditions after oak decline? (2) What are the ecological factors that explain the successful response of woody species to changes in light and thermal conditions? In the monitoring plot, the structural condition of specimens only above 8.0 m was observed. After the appearance of oak decline some Acer campestre, Cornus mas and Acer tataricum specimens appeared that reached between 8.0-13.0 m in height. Significant differences were revealed between top canopy density and foliage cover of the subcanopy and between top canopy density and mean cover of field maple. The findings of the study indicate that the forest responded to oak decline with significant structural rearrangement in the shrub layer and that three woody species compensated for the remarkable foliage loss in the top canopy. These species formed a second crown layer directly below the canopy formed by oaks.
ABSTRACT:The serious oak decline was reported for the 1979-80 period and 63.0% of adult oaks died in a mixed oak forest in the Síkfőkút site, Hungary. The data were used to obtain (1) quantitative information on diversity indices of shrub layer and shrub canopy, including foliage cover percentage of the shrub layer, mean cover of shrub species before and after the oak decline and (2) structural information on shrub basal area and shrub foliage arrangement. Since 1972 we have determined diversity indices, cover percentage and basal area of shrubby vegetation on the monitoring and plus plots. A negative relation was detected between Shannon-Wiener and Evenness indices of the shrub layer and living oak tree density. A positive relation was confirmed between basal area and mean cover of dominant woody species (Acer campestre, Acer tataricum and Cornus mas). The mean cover of shrub species except of A. campestre increased non-significantly after the oak decline on the 48 m × 48 m plot. The findings of the study indicate that diversity indices of the shrub layer and mean cover of A. campestre can be used as a principal indicator of natural disturbance in the studied mature stand and the species of the shrub layer respond differently to the decreasing stand density.
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