The effect of silvicultural management on the genetic diversity of a mixed Nothofagus forest in Lanín Natural Reserve, Argentina

• The seed cut has not altered genetic diversity of Nothofagus at species level.
• No change in hybrid proportion was found after harvesting.
• The global genetic diversity of mixed Nothofagus forest decreased after harvesting.
• The decreased diversity was due to changes in regeneration species proportion.

Knowledge of the impact of forest management practices is crucial to allow the use of natural resources while ensuring the sustainability of genetic variation, which is essential for the potential adaptive capacity of forests. The main objective of this work was to study the effects of a seed cut on the genetic diversity of a mixed Nothofagus forest in northwestern Andean Patagonia. Silviculture based on the shelterwood system was carried out in stands composed of Nothofagus dombeyi, Nothofagus nervosa and Nothofagus obliqua, located in Lanín Natural Reserve (Neuquén province, Argentina). Through intensive sampling of pre (mature trees) and post (regeneration) harvest populations of all three species from a 3-ha plot established after 20 years of the silvicultural intervention, in combination with microsatellite genotyping (more than 2000 individuals with 15 markers), we determined that modification of relative abundance of species in the post-harvest population that followed the implemented management had altered the global genetic diversity of the mixed forest; however, no impact was detected at species level in the entire plot or in two subplots with different species proportions. Pollen and seed dispersal from the surrounding areas may have contributed significantly to maintaining both genetic diversity in the post-harvest natural regeneration and the low differentiation between this and the pre-harvest gene pool in all species. The use of species-specific markers allowed us to determine that the level of introgressive hybridization was not changed by management; however, further studies are required to evaluate whether this practice influences the directionality of introgression.