Evaluation of silvicultural effects on the genetic structure of natural regenerated beech stands (Fagus sylvatica L.)

摘要

Aim of the study was to assess the silvicultural effects of the intensity of thinning from above on the genetic structures of natural regenerated beech stands. In a second step the random distribution of genotypes was tested. For the assessments twosilvicultural test trials located in Lower Saxony (Luss and Uslar) were selected. In each test site the moderate and heavy thinning from above were compared to an unthinned plot. The sample size in each plot varied from 243 to 442 trees. The genetic variability at isozyme gene loci was estimated by isozyme analysis using starch gel electrophoresis. The genetic structure was determined using 9 polymorphic gene loci. The distribution of genotypes within the blocks was calculated by Clark-Evans-Index. Compared to the unthinned plots the genetic distance was not increased from moderate to heavy thinning. Within the blocks genotypes were not inevitably randomly distributed. A trend to aggregation was observed for homozygote genotypes if the allel frequencywas less than 25 percent. Especially homozygote individuals with rare alleles showed significant aggregation for minorpolymorph enzyme gene loci. For the parameters Clark-Evans-Index and genotype frequency a correlation coefficient of r=0.61~(***) was found. It is to conclude that microsite genetic differentiation due to aggregation explains more of the existing variation than directional selection caused by thinning grades. Aggregation of genotypes is also to be expected for directly adaptative gene markers. Consequences for silvicultural test trials are discussed.