8  Outline of research objectives and thesis sections

To summarise, the ultimate objective of this thesis is to determine whether genetic variation in a foundation species, aspen, affects the community composition of its epiphytes, and if so, are these differences caused by clonal differences in either bark texture or secondary chemistry? These questions are tackled both in a natural population of aspen at Invertromie, and in a clonal trial of aspen planted at two contrasting sites in Scotland.

The thesis is arranged into the following sections whose contents are described below:

8.1 Outline of thesis sections

Section X

Five wild aspen clones were selected from a larger population in Strathspey, Scotland. Bark texture and bark secondary chemistry were measured for each clone to ascertain whether genotypes differ significantly for these traits.

Section X

Using the same aspen clones as for the previous chapter, epiphyte communities were sampled on each clone to ascertain whether genotypes differ significantly for this aspect of their extended phenotype. These results were analysed in conjunction with the results for bark texture and secondary chemistry to discern whether these traits are significant in shaping epiphyte community structure.

Section X

A total of 27 aspen clones, replicated across two sites in Scotland in a randomized block design, were sampled to test for differences between genotypes in bark secondary chemistry and epiphyte community. Variation in bark chemistry was used as an explanatory variable to attempt to explain observed variation in epiphyte community structure between clones.

Section X

This final section synthesises results from the preceding experimental sections (X-X), comparing and contrasting findings of the different systems used and variation observed in bark physical traits and epiphytes. Conclusions are drawn from the main results and suggestions made for further research and conservation strategies.