CONICET | Buscador de Institutos y Recursos Humanos

Extensive knowledge of the ecological and genetic consequencesof implementing management practices (i.e. logging) in natural ecosystemsis of fundamental importance to conservation action. Accordingly,characterization of forest genetic resources in managed vs non-managedstands may help ensure the long-term persistence of genetic diversity.The main objective of this study was to evaluate the impact of managementpractices on the genetic diversity and spatial genetic structure ofcontrasting forests, through an age-class sampling design and the use ofmicrosatellite markers. We evaluated the impact of logging in threepopulations of Nothofagus pumilio, a dominant tree species in Patagoniantemperate forests, by comparing managed and non-managed stands in eachpopulation. Selective extraction of best-featured individuals, i.e. thosewith forestry aptitude, such as higher trees with straight trunks andgood sanitary conditions, was performed between 1990 and 2004. One of thestudied sites was located in a state-protected area while the others wereon private land affected by grazing. At each managed stand over-maturetrees (MF-O), adult remnant trees (MF-A) and seedlings representingforest regeneration (MF-R) after silvicultural management were sampled.In non-managed stands age classes were restricted to adults (CF-A) andseedlings (CF-R). A minimum of 30 individuals per age class werecollected, totalling 454 samples which were genotyped at sixmicrosatellite loci.Non-significant differences in genetic diversity were found betweenmanaged and natural woods in all populations. A trend towards decreasingfrequencies or even allele loss among remnant adults of logged standscan, however, be interpreted as a sign of impact, probably a consequenceof genetic drift. Each site showed particular, different outcomes withrespect to genetic structure. While in Pop1 (Huemules, 42°S) significantgenetic differentiation was found between management treatments,admixture of genetic clusters (Bayesian clustering and DAPC analysis)occurred in Pop2 (Guacho Lake, 43°S) and no genetic structure was foundin Pop 3 (Engaño Lake, 43°S). Post-harvest genetic contact betweencontrasting stands is likely. A Landscape Interpolation Analysis showedclusters of individuals (shared genotypes) spatially restricted formanaged stands, whereas a random spatial distribution characterizedcontrol forests. Therefore, it is possible that management affected anddisrupted the genetic structure.The different genetic patterns revealed for each population call forsite-by-site interpretation. Differential intensity and frequency ofmanagement practices, presence/absence of livestock in the forest, andevolutionary history may all have combined to delineate current geneticdiversity.

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