Abstract
The landscape-scale extinction of a tree species may have a negative impact on diversity of associated epiphytic species. We used ordination and hierarchical clustering methods to assess landscape and the community level effects of reduction in the abundance of European ash Fraxinus excelsior, caused by ash dieback, on the associated epiphytic lichen biota in Białowieża Forest (Poland)—the best preserved forest complex in Central Europe. At the landscape level ash decline impact on the biota of ash-associated epiphytic lichens was weak, due to the high diversity of tree species, which may serve as potential alternative hosts. At this level, oak and hornbeam are the most important alternative hosts, assuring the maintenance of ash-associated epiphytic lichens. Lime, alder, and hazel appeared to be less important but still may serve as substitute phorophytes to approximately 2/3 of the ash-associated lichen biota. About 90% of epiphytic biota are likely to survive on the landscape scale. However, at the community level of alder-ash floodplain forest, where ash was dominant, about 50% of ash-associated epiphytic lichen species are threatened by ash dieback. Our results highlight the importance of a spatial scale in conservation biology. Protection of large forest areas with rich diversity of phorophyte trees increases chances of survival of the associated epiphytic organisms.
Highlights
The dieback of European ash Fraxinus excelsior has been reported since the early 1990s
The main aim of our work was to estimate whether the ash dieback is driving the loss of lichen epiphytes diversity amongst forest communities not affected by humans, on the same scale as was reported in Northern and Western Europe, and what other phorophyte tree species can be considered as important alternative hosts for lichens associated with ash
At the tree phorophyte level we revealed that communities of lichen epiphytes growing on the bark of oak, lime, ash, and hornbeam were characterized by high values of WEIV-F, species richness, and Shannon diversity (Fig. 4a; Table 1)
Summary
The dieback of European ash Fraxinus excelsior has been reported since the early 1990s. A severe dieback of ash, which includes trees in all age stages (Gross et al 2014a; Needham et al 2016; Enderle et al 2018), can be observed in most European countries (Bakys et al 2009a, b; Kowalski and Holdenrieder 2009a, b; Allen et al 2010; Beck et al 2016; Coker et al 2019) It is caused mainly by the fungus Hymenoscyphus fraxineus, which induces wilting and loss of leaves, thinning of crowns, darkening of wood, necrosis and neoplastic changes on trunks and branches, and leads to the deaths of trees (Baral et al 2014; Gross et al 2014b), but other pathogens that weaken this tree are reported, e.g. fungus Rigidoporus ulmarius (Lücking et al 2019). Despite the fact that some populations of ash may be resistant to infections by H. fraxineus (Enderle et al 2015; Pušpure et al 2017), which creates an opportunity for ash recovery, the observed regeneration of ash has not brought the expected results (Enderle et al 2018)
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