Identifying Substitute Host Tree Species For Epiphytes: The Relative Importance Of Tree Size And Species, Bark And Site Characteristics

Questions Can bark characteristics be used to determine the suitability of trees to host epiphytic bryophytes and lichens or are other tree and site characteristics more important? Identification of substitute hosts is required in the face of epidemic tree deaths due to diseases that are a threat to affiliated epiphytic communities. We assess the suitability of seven phorophytes to host the epiphytes associated with the UK native oak species, Quercus petraea and Quercus robur, which are currently threatened by a range of pests and pathogens. Location Six botanic gardens and arboreta across the UK. Method We recorded the site, habitat, tree (height, diameter at breast height [1.3 m; DBH], percentage canopy cover) and bark characteristics (pH, conductivity, density, water-holding capacity, hardness, topography) and epiphytic community composition on Acer pseudoplatanus, Castanea sativa, Fagus sylvatica, Fraxinus excelsior, Quercus cerris, Quercus petraea, Quercus robur, Quercus rubra and Tilia x europaea. In total 230 trees were surveyed across the six sites. Results Comparisons between all trees showed significant correlations between similarities in community composition and bark characteristics. However, "tree characteristics" (species, height, DBH and canopy over) explained more of the variation in epiphytic community composition than bark and site characteristics. Phorophytes with similar epiphytic community richness or composition to native oaks did not necessarily have similar bark characteristics. Non-native oaks and the non-native hybrid Tilia x europaea supported similar epiphyte communities to the native oaks and are suggested as substitute phorophytes. Conclusion Using bark traits is not a reliable method to assess the suitability of substitute phorophytes to conserve epiphytic communities. Instead, the epiphytes hosted by a wider range of phorophytes should be recorded to allow an assessment of their suitability as substitute hosts and hence aid management decisions on replacement phorophytes following tree loss.