Direct seeding of silver fir (Abies alba Mill.) to convert Norway spruce (Picea Abies L.) forests in Europe: A review

- Fluctuations in use of direct seeding of silver fir proven by historical sources.
- Key factors of influence were identified, distinguished by development stage.
- Aspects of natural regeneration cycle directly linked to seeding techniques.
- Ecological complexity is included in a decision pathway for management.

The direct seeding method of artificial regeneration has a long tradition in silvicultural management. The main application of the direct seeding of silver fir (Abies alba Mill.) today occurs in the context of the conversion of Norway spruce stands in central Europe. Although direct seeding is often considered to closely resemble natural regeneration in many respects, tree planting is currently more commonly employed in forestry. Presented in this paper is an extensive historical review showing the variety of facets associated with and experiences of direct seeding gleaned through scientific experiments or based on forestry practice. This review also illustrates the fluctuating practical relevance of the direct seeding of silver fir depending on the prevailing objectives of forest owners, harvesting methods, forest structures and the possibilities for technical implementation. An overview of the available ecological knowledge of the development stages and processes within the natural regeneration cycle of silver fir is provided, highlighting the most relevant environmental factors and the resources determining the success of natural regeneration. Having identified these factors, the individual technical steps involved in direct seeding can be analysed. The means by which the individual steps in the direct seeding approach can be used to manipulate environmental factors and microsite conditions such as the density of overstorey shelter, soil and seedbed preparation, and to reduce competition pressure to optimise the direct seeding of silver fir are outlined. Finally, on the basis of the analyses presented, these complex relationships are integrated in a step by step decision pathway to provide an individual forest stand decision-making process. This ecologically based approach can improve the success of direct seeding and may allow for the adaptation of the direct seeding process to suit individual forest stand conditions. Consequently, the growing efforts to convert and enrich homogenous Norway spruce stands by means of the direct seeding of silver fir can be promoted in a close-to-nature way, while employing controlled silvicultural measures.