Background
The authors write that "with increasing temperatures and dryer summers [as predicted by various climate models], areas nowadays covered by beech forests are expected to shrink tremendously," but they say that "if individuals at the dry distribution limits [of the species: Fagus sylvatica L.] are adapted to lower moisture availability, F. sylvatica might contain the genetic variation for the continuation of beech forests under climate change," even in areas that are predicted to become devoid of the trees.

What was done
In an investigation into the strength of this hypothesis, Pluess and Weber used an AFLP (Amplified Fragment Length Polymorphism) genome scan approach that was designed to explore the "neutral and potentially adaptive genetic variation in Fagus sylvatica in three regions [within the lowland forests of Switzerland] containing a dry and mesic site each," after which they "linked this dataset with dendrochronological growth measures and local moisture availabilities based on precipitation and soil characteristics."

What was learned
The two Swiss scientists report that a "potential for adaptation to water availability" was reflected in observed outlier alleles that "indicated microevolutionary changes between mesic and dry stands." And they note, in this regard, that "while Rose et al. (2009) found adaptation to drought in a common garden experiment with seedlings originating from provenances which were more than 1000 km apart," they found genetic differentiation in relation to water availability in neighboring stands.

What it means
In light of this set of real-world observations, Pluess and Weber conclude that "dispersal across large distances is thereby not needed for the spread of 'preadapted' genes in F. sylvatica," for the trees apparently do indeed contain the genetic material needed for "the continuation of beech forests under climate change," even in areas that have been predicted to become too dry for F. sylvatica trees to survive.

Reference
Rose, L., Leuschner, C., Kockemann, B. and Buschmann, H. 2009. Are marginal beech (Fagus sylvatica L.) provenances a source for drought tolerant ecotypes? European Journal of Forest Research 128: 335-343.