Genetic aspects related to natural and artificial regeration of Douglas-fir in Bavaria

One of the most important factors when planting Douglas-fir is choosing the most suitable provenance for the site. Under climate change, genetic diversity as the basis for adaptation is of increasing importance. Both aspects, provenance and genetic diversity, have to be considered if natural regeneration of adult stands or planting of new stands are discussed. Numerous provenance trials have proven that the most suitable provenances for Bavaria originate from the coastal region west of the Cascade Mountains in Washington (Pseudotsuga menziesii var. menziesii). The interior variety (Pseudotsuga menziesii var. glauca and P. menziesii var. caesia) is unsuitable both because of growth rate and susceptibility to needle cast. However, not only coastal Douglas-fir was planted in Bavaria. Isozyme analysis showed that around 20% of the Bavarian stands represented interior Douglas-fir or a mixture of coastal and interior variety. Through natural regeneration the genetic structure of the adult trees is passed on to the following generation. If gene flow through pollen or seed from neighbouring stands occurs, significant changes in the genetic composition of natural regeneration in comparison with the adult generation will be observed. The same is true for the seed collected from adult stands. This must be taken into consideration when stands are selected as registered seed collection stands. Stands with low genetic diversity and mixture of green and gray variety of Douglas-fir have to be excluded from seed collection. To maintain an appropriate level of genetic diversity in the seed, cones should be collected from at least 20 trees per stand. This should be considered the absolute minimum. Concerning the level of genetic diversity in seed collections from Germany, West Washington (USA) and France (seed orchards), no clear differences were observed.