Population genetics of silver fir (Abies alba Mill.) in the Northern Black Forest – preconditions for the recolonization of windthrow areas and associated ectomycorrhizal communities
Facing climate change, we expect an increasing frequency of extreme weather events such as storms that affect forest ecosystems. In the last decades, several storm events in Central Europe have damaged huge areas of forest stands that have to be recolonized. Symbiotic systems between trees and ectom...
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|Facing climate change, we expect an increasing frequency of extreme weather events such as storms that affect forest ecosystems. In the last decades, several storm events in Central Europe have damaged huge areas of forest stands that have to be recolonized. Symbiotic systems between trees and ectomycorrhizal (ECM) fungi play a decisive role for the stability and the vitality of trees. In the context of promoting the rare, but ‘stabilizing’ tree species silver fir in mountain forests and facing the recolonization of windthrow areas, three fir populations were genetically investigated in the Northern Black Forest, Germany. For this purpose, in a first step nuclear microsatellite (nSSR) markers were developed for silver fir. Fir trees of different ontogenetic stages (adults, saplings, seedlings) were genotyped at six nSSR loci and analysed in terms of diversity and abundance of the associated ECM fungi.
The results demonstrate that silver fir populations in the Black Forest maintain a suitable genetic potential with high diversity within and less differentiation among populations. The remaining natural fir regeneration on the windthrow area did not show a reduced genetic diversity in comparison to the adjacent forest stands which include different generations. In addition, dispersal characteristics (gene flow) of firs revealed a sufficient seed and pollen flow of at least a few hundred meters from the mother trees. A high number of mother trees contributed to the seed dispersal and led to a multifaceted seed entry, even into the windthrow areas. Beyond, the analysis of the associated ECM fungi exhibited an identical spectrum of ECM fungi on the windthrow area and in the forest stand. We did not find evidence that the age of the trees can be regarded as driving factor for associated ECM communities on the population level. Based on the individual tree, adults host a higher number of ECM fungi than juveniles. Since the pre-windthrow offspring exhibited a well-balanced ECM profile they serve as ‘reservoir hosts’ for post-windthrow offspring promoting their vitality. Finally, we examined the data with respect to a possible correlation between host genotypes and associated ECM fungi. It became evident that the genomic background of silver fir as represented by single-locus variation has an effect on the composition of the associated ECM community. Consequently, ECM communities may be considered as extended phenotypes of the host populations. Protecting silver fir as a means of forest gene conservation therefore implies not only the tree species, but as well the interacting ECM community as part of the ecosystem.
Based on the overall findings including tree genetic, dispersal and mycological aspects, silver fir populations in the Black Forest provide an appropriate basis for natural regeneration processes within the forest stand as well as for the recolonization of windthrow areas. Natural regeneration is an appropriate method for the reintroduction of larger proportions of silver fir in the Black Forest.