2.4.1. Case Study 4: genetic structures in pure and
mixed oak (Quercus spp.) forests in Switzerland
Mixed forests composed of Quercus petraea and Q.
robur proved to be on average slightly more variable
than pure populations of both species. However, an
analysis of genotypic structures revealed higher
inbreeding coefficients in mixed forests, which was
attributed to a Wahlund effect. Thus, the increased
levels of genetic variation in mixed forests are an
outcome of growing semi-isolated populations of
closely related species in the same area. The mixture
of Q. petraea and Q. robur enhances not only evolutionary
adaptability by promoting genetic variation,
but also the physiological adaptive potential of oak
forests since the species are believed to be differentiated
from each other with regard to important adaptive
properties such as tolerance against water logging.
Q. pubescens, another interfertile oak, harbours less
variation than the more common Q. petraea and Q.
robur.