Identifying substitute host tree species for epiphytes: The relative importance of tree size and species, bark and site characteristics

Abstract

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 × 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 × 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.

Importance of conserving large and old trees to continuity of tree‐related microhabitats

“…For instance, in both forest types, the occurrence of epiphytes increased with elevation, which is in accordance with other studies from European temperate forests and may be connected to higher precipitation (Asbeck et al., 2019; Paillet et al., 2019). Moreover, of the four studied tree species, sycamore exhibited an increased occurrence of epiphytes, probably due to different bark characteristics, such as water‐holding capacity, roughness, and chemical properties (Mitchell et al., 2021). Consistent with other studies (Asbeck et al., 2019; Paillet et al., 2019), broadleaved species had higher overall TreM richness than conifers.…”

Quantification and Variation of Microclimatic Variables Within Tree Canopies - Considerations for Epiphyte Research

“…For the epiphytes, tree height has been one of the key predictive variables of epiphyte richness in a local context (Flores-Palacios and García-Franco, 2006;Krömer et al, 2007). Taller trees often harbor a higher richness, biomass and abundance of epiphytes, compared to smaller trees (Flores-Palacios and García-Franco, 2006;Elias et al, 2021;Mitchell et al, 2021). The stratification of epiphytes along the vertical profile of trees has thus been the focus of several scientific studies in the past (see Johansson, 1974 andZotz, 2007).…”

Stand-Level Variation Drives Canopy Water Storage by Non-vascular Epiphytes Across a Temperate-Boreal Ecotone

“…In the absence of macroclimatic predictors of epiphyte biomass and potential water storage, forest type appeared to be a strong driver of epiphyte community properties. Non-vascular epiphytes communities are known to be strongly influenced by host tree species, reflecting effects of bark texture, chemistry, and light availability (Ellis, 2012;Mitchell et al, 2021). Canopy structure also influences the partitioning of rainfall between throughfall and stemflow (Levia and Frost, 2003;Levia et al, 2019;Van Stan et al, 2020), which can further influence bole epiphyte communities.…”