Beech bark necrosis: partition- ing the environmental and spatial variation of the damage severity in Central and South-Eastern Europe

Abstract

The beech bark necrosis (BBN) infestation severity of European beech (Fagus sylvatica L.) was assessed in regions of Central (CE) and South-Eastern Europe (SE). Altogether more than 10,000 trees were sam- pled at 114 sites. Using variation partitioning method, we examined the pure and shared effects of stand, site, climate and spatial sets of variables on mean BBN severity. Our rating included (i) the whole stand, (ii) tree social status classes, (iii) canopy (C) and (iv) understory (U) trees sepa- rately. We found that C trees were less affected by BBN than sub-canopy and U trees in both regions. There were found inter-regional differences in amount of explained variability (25.4-73.9%) for whole stand BBN and in the sensitivity of C and U trees to the environmental gradients. The analy- sis revealed that the climate and spatial variables followed by stand vari- ables had the largest marginal effects on mean BBN severity in all models, while the site set of variables had the weakest one. More than half of the explained variation was shared among four sets of variables in SE, contrary to CE. Except to U trees in SE, the effect of climate - pure or spatially structured - remained the highest also after partitioning of variance; more in SE than in CE. Taking into account positive association between mean annual temperature and mean BBN severity in C trees in SE, reinforced negative effect of climate change on the necrosis might be expected to be more serious mainly in low situated beech forests there. Promoting the tree species diversity in areas with higher incidence of beech bark necro- sis, i.e. in low altitudes in SE, could reduce the susceptibility of forests to the necrosis at regional level in the future. For better understanding of the relative importance of environmental and spatial variables on BBN sever- ity, further research performed on finer spatial scale (extent and grain) is necessary, along with accounting for pathogens involved in the infestation.