PhD defence: Eva Ortvald Erichsen

Eva Ortvald Erichsen defends her thesis,

Genetic diversity in ancient forests and glacial refugia
       – a potential resource for the future forests in Denmark?

Associate Professor Ole Kim Hansen, IGN
Professor Emeritus Jørgen Bo Larsen, IGN

Assessment Committee:
Senior Scientific Officer Stephen Cavers, Centre for Ecology & Hydrology – UK
Senior Researcher Tor Myking, Norwegian Institute of Bioeconomy Research (NIBIO) – Norway
Associate Professor Lene Rostgaard Nielsen (chair), IGN

Due to climate change we are approaching a global crisis, in which conditions such as temperature and precipitation convene towards extremes. In order to combat this, trees and forests undeniably serve a principal function. They can act as ecosystem engineers, store carbon, harbour biodiversity and serve as construction material with low emission costs. Conversely, forests themselves are affected by a changing climate, as long lived trees will have to adapt to a new environment while not being able to migrate fast. On top of this are novel pests and diseases also posing a selective pressure when present. The ability to adapt is thus vital and the foundation for this is genetic variation. In Europe the adaptive potential of forests is, at least potentially, constrained by a reduced amount of genetic variation as a consequence of past genetic bottlenecks created by glaciations and, in more recent historical time, fragmentation of forest areas by humans.
The work in this thesis examines genetic variation with relation to Danish forests primarily by use of molecular genetic markers, but other methods were also used; e.g. simulation modelling.
Despite heavy fragmentation there are still remnants of ancient forests left in Denmark. The forest tree Tilia cordata (small-leaved lime) is considered an indicator for these forests as it is primarily found there. In this study, the fine-scale genetic structure was mapped and despite fragmentation and small population sizes, the study revealed high degree of genetic diversity, surprisingly little genetic differentiation among populations and a large proportion of clonal structures in several of the studied populations. The data was subsequently used in a simulation model, to re-trace the growth and development of the population. The simulation revealed that the rise and death of clone groups are very dynamic and that the population of T. cordata in Bolderslev forest is of old age due to the high number of somatic mutations.
Another native species, Fraxinus excelsior (common ash), is currently under enhanced selective pressure due to Ash die-back. With F. excelsior as an example the aim in this study was to establish whether populations in glacial refugia contain a higher degree of genetic variation which could then act as a source of enrichment of Danish forests. This was approached by a comparison between European populations and populations from the refugial area of the Hyrcanian forest in Iran. The results revealed high genetic diversity in the Hyrcanian forest and that the gene pool is rather differentiated from the European forests of F. excelsior. Seeds from the Hyrcanian forest could thus act as a means for genetic enrichment of Danish forests.
Traditionally, there is a long history of using non-native forest tree species in Denmark, one of them is Abies alba (silver fir). In A. alba, provenances from the isolated glacial refugium Calabria (southern Italy) have been found to perform very well in Denmark. This study investigated whether populations from Calabria holds an especially high potential for local adaptation, as former studies has found them to be very diverse genetically. That Calabrian populations are more locally adapted could not be concluded. Nevertheless, signals indicating that the populations were adapted to drought were obtained. This could be important as summer drought is one of the expected consequences of climate change.

The thesis is available for inspection at the PhD administration office 04.1.413 at Øster Voldagde 10.