The impact of the contact zone between two migration routes of silver fir (Abies alba Mill.) in the western Balkan area

Silver fir (Abies alba Mill.) is one of the most important forest tree species in the western Balkan area both economically and ecologically. Its distribution has been the subject of scientific research for many years because silver fir from these areas displays very interesting morphological and genetic differentiation. The objective of this research was to determine the boundary of gene introgression of silver fir deriving from the Apennine and Balkan glacial refugia in the western Balkan populations with the use of isoenzymes. Nine enzyme systems were studied in 24 populations from Bosnia and Herzegovina and Croatia, and polymorphic gene loci and their allelic types were scored. The analysis of general genetic parameters did not allow for any conclusion, and neither did the analysis of genetic distances. However, statistical analysis of allele distribution showed the populations from Croatia (Gerovo, Fužine, Skrad and Vrbovsko) to be distinctly different from those from Bosnia and Herzegovina. Populations along the contact zone (Grmeč, Oštrelj, Tičevo and Glamoč) and from the eastern part (from central and east Bosnia and Herzegovina) did not show any regular grouping or clinal variability. This is attributed to high ecological diversity, fragmentation and the occurrence of genetic drift. Alleles originating from the Apennine refugium are also present in trees in eastern Bosnia. The results suggest that silver fir originating from the Balkan refugium was more widely distributed in the past, but is now retreating relative to that originating from the Apennines.