Tracking the origin of silver fir plantations along the boundary between different genetic clusters in central Apennines: Implications for their management

Reforestation with native species determines that autochthonous populations and plantations are often within the reach of gene flow. To address efficient strategies for forest plantation management it is fundamental to track the origin of reforestation material, in order to limit potentially detrimental effects on the adaptive potential of autochthonous populations. The use of genetic information to determine the origin of plantations is very effective when historical data about reforestation programs are absent. The main objectives of our study were to assess the origin of silver fir plantations in the Majella National Park (Central Apennines) and to compare genetic diversity parameters between plantations and natural stands. The latter objective is particularly relevant to evaluate the levels of genetic variation in plantations of local origin and to evaluate their suitability as already established reforestation stands. A comprehensive genetic dataset (1619 individuals from 33 natural silver fir populations genotyped at 16 nuclear microsatellite markers) was built to characterize potential seed sources for 10 plantations from the Majella National Park. Their genetic origin was assessed through combining the results of Bayesian assignment tests and analyses of genetic differentiation. Based on the genetic structure characterizing natural populations, we were able to definitely assess the origin of most of the planted individuals. Five plantations were established using material which most likely originated in natural populations that are only 10-20 km distant. These plantations harbour levels of genetic variation similar to the surrounding natural populations and are, therefore, to be considered valuable local forest genetic resources. The other five plantations consist either partially or entirely of allochthonous individuals which are similar to Alpine and northern Apennine populations. To avoid exotic gene flow to nearby autochthonous populations, we suggest the removal of plantations in which allochthonous individuals are present before they reach sexual maturity. However, before taking such action, we recommend the monitoring of the relative performance of different provenances, i.e. plantations entirely made by either putatively autochthonous or undoubtedly allochthonous material. Such an investigation would allow a thorough ex post evaluation of past reforestation programs. To conclude, our results show that genetic data can provide essential information for general decision-making in forest plantations management and, considering the thorough characterization of silver fir genetic structure in this multi-refugial area, such information can be particularly useful for a correct management of Apennine plantations.