Response and mortality of beech, fir, spruce and sycamore to rapid light exposure after large-scale disturbance

Abstract

Physiological response to rapid light exposure due to canopy disintegration in young beech, fir, Norway spruce and sycamore trees was measured in three consecutive years after the severe ice storm in 2014 and after windthrow in 2017. Nitrogen amount (Ntot), maximum 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 with number of seedlings per hectare were compared between damaged and undamaged sites, with young trees gradually adapting to light conditions in the two years following the two disturbance events.Nitrogen levels were in the optimal range for all species studied. Rapid exposure to elevated light reduced efficiency in fir and increased efficiency in beech and especially sycamore. No differences in response were observed in spruce. Assimilation efficiency, where both tree species were equal, shifted towards shade. Recovery was similar for all species studied after both disturbances: better after the windstorm, compared to the ice storm, indicating the severity of the event. Reductions in seedling numbers followed the pattern observed for physiological traits.