No abstract

Despite plant secondary metabolites being major determinants of species interactions and ecosystem processes, their role in the maintenance of biodiversity has received little attention. In order to investigate the relationship between chemical and biological diversity in a natural ecosystem, we considered the impact of chemical diversity in individual Scots pine trees (Pinus sylvestris) on species richness of associated ground vegetation. Scots pine trees show substantial genetically determined constitutive variation between individuals in concentrations of a group of secondary metabolites, the monoterpenes. When the monoterpenes of particular trees were assessed individually, there was no relationship with species richness of associated ground flora. However, the chemical diversity of monoterpenes of individual trees was significantly positively associated with the species richness of the ground vegetation beneath each tree, mainly the result of an effect among the non-woody vascular plants. This correlation suggests that the chemical diversity of the ecosystem dominant species has an important role in shaping the biodiversity of the associated plant community. The extent and significance of this effect, and its underlying processes require further investigation.

Climate change is expected to have an impact on plant communities as increased temperatures are expected to drive individual species' distributions polewards. The results of a revisitation study after c. 34 years of 89 coastal sites in Scotland, UK, were examined to assess the degree of shifts in species composition that could be accounted for by climate change. There was little evidence for either species retreat northwards or for plots to become more dominated by species with a more southern distribution. At a few sites where significant change occurred, the changes were accounted for by the invasion, or in one instance the removal, of woody species. Also, the vegetation types that showed the most sensitivity to change were all early successional types and changes were primarily the result of succession rather than climate-driven changes. Dune vegetation appears resistant to climate change impacts on the vegetation, either as the vegetation is inherently resistant to change, management prevents increased dominance of more southerly species or because of dispersal limitation to geographically isolated sites.

Heritable variation in plant secondary compounds in dominant species has been hypothesised to effect ecosystem function and the structure of associated assemblages of plants, microbes and animals. The functioning of this extended phenotype in relation to the understorey vegetation composition was tested within a boreal forest system dominated by Pinus sylvestris which contains a range of monoterpenes, the composition of which is largely under genetic control. A variance partitioning approach was adopted to identify the relative importance of tree chemistry, environment, spatial location and tree architecture in controlling the distribution of species in the ground flora under individual trees. The monoterpene composition of the pine needles appeared to contribute significantly to controlling understorey vegetation composition, but was less important than environmental factors, though similar to spatial factors. Thus there appears to be a link between variation in the chemical composition of the single, dominant tree species within this system and the pattern of occurrence and abundance in other species at the same trophic level.

No abstract

No abstract

No 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.