Divergent response of European beech, silver fir and Norway spruce advance regeneration to increased light levels following natural disturbance

Abstract

A comparative study of young European beech, silver fir and Norway spruce in the Slovenian mixed forest stands was made at four locations, exposed to the rapid canopy disintegration after the severe ice storm in 2014. Nitrogen amount (Ntot), Leaf mass per area (LMA), maximal Assimilation response to light (Amax) and Quantum yield (Φ) were measured in three categories of different light intensities under closed canopy with Indirect Site Factor (ISF)<15%, at the forest edge (15%<ISF<25%) and in the open (ISF>25%). Tree responses were compared between damaged plots – rapidly exposed to light and undamaged sites, where young trees gradually adapted to the light environment during two years (2015 and 2016) after the disturbance event.Nitrogen content of all three species was within optimal range values, highest in the open and lowest under canopy conditions on every plot. Rapid exposure to increased light levels affected most directly fir in the category of forest edge and under open canopies. Contrary to fir, beech responded in a favourable way, while no differences in response were evident in spruce. Assimilation efficiency, where both fir and beech were equal shifted towards the shade in both years.