Why sycamore and beech fall short: assessing the compensatory potential of alternative hosts for ash-associated saproxylic fungi

The spread of Hymenoscyphus fraxineus and the ash dieback epidemic threatens the biodiversity associated with European ash ( Fraxinus excelsior ). Following a loss of ash from the landscape, sycamore ( Acer pseudoplatanus ) and beech ( Fagus sylvatica ), are expected to dominate replacement by natural colonisation. Here we analyse fruit body records using a null modelling framework to examine the macro-fungal diversity associated with ash within the UK and Ireland. In total, 55 species were significantly associated with ash, 22 of which exhibited a high level of dependency on F. excelsior substrates. Records of saproxylic fungi pertaining to ash were compared with those of the two dominant replacement species. There were large ecological distances between the ash community and the communities recorded on the alternative hosts, indicating that both beech and sycamore are likely to function poorly as compensatory analogues for ash in terms of the saprotrophic fungal communities they support.