title: Disturbance and density-dependent processes (competition and facilitation) influence the fine-scale genetic structure of a tree species' population.
abstract: OBJECTIVE
  Disturbances, dispersal and biotic interactions are three major drivers of the spatial distribution of genotypes within populations, the last of which has been less studied than the other two. This study aimed to determine the role of competition and facilitation in the degree of conspecific genetic relatedness of nearby individuals of tree populations. It was expected that competition among conspecifics will lead to low relatedness, while facilitation will lead to high relatedness (selection for high relatedness within clusters).
  
  
  METHODS
  The stand structure and spatial genetic structure (SGS) of trees were examined within old-growth and second-growth forests (including multi-stemmed trees at the edge of forests) of Nothofagus pumilio following large-scale fires in Patagonia, Chile. Genetic spatial autocorrelations were computed on a spatially explicit sampling of the forests using five microsatellite loci. As biotic plant interactions occur among immediate neighbours, mean nearest neighbour distance (MNND) among trees was computed as a threshold for distinguishing the effects of disturbances and biotic interactions.
  
  
  RESULTS
  All forests exhibited a significant SGS for distances greater than the MNND. The old-growth forest genetic and stand structure indicated gap recolonization from nearby trees (significantly related trees at distances between 4 and 10 m). At distances smaller than the MNND, trees of the second-growth interior forest showed significantly lower relatedness, suggesting a fading of the recolonization structure by competition, whereas the second-growth edge forest showed a positive and highly significant relatedness among trees (higher among stems of a cluster than among stems of different clusters), resulting from facilitation.
  
  
  CONCLUSIONS
  Biotic interactions are shown to influence the genetic composition of a tree population. However, facilitation can only persist if individuals are related. Thus, the genetic composition in turn influences what type of biotic interactions will take place among immediate neighbours in post-disturbance forests.
authors.affiliation: Centro de Investigación en Ecosistemas de la Patagonia (CIEP) Conicyt-Regional R10C1003, Universidad Austral de Chile, Camino Baguales s/n, Coyhaique 5951601, Chile, alex.fajardo@ciep.cl.
authors.forename: Alex
authors.initials: A
authors.lastname: Fajardo
authors.affiliation: Laboratorio de Genómica y Biodiversidad, Departamento de Ciencias Básicas, Universidad del Bío-Bío, Casilla 447, Chillán, Chile.
authors.forename: Cristian
authors.initials: C
authors.lastname: Torres-Díaz
authors.affiliation: Université Grenoble Alpes, Laboratoire d'Ecologie Alpine (LECA), F-38000 Grenoble, France and CNRS, LECA, CNRS F-38000 Grenoble, France.
authors.forename: Irène
authors.initials: I
authors.lastname: Till-Bottraud
mesh_terms: D000483:Alleles; D006579:Heterozygote; D018515:Plant Leaves / Q000502:physiology; D011157:Population Dynamics; D013045:Species Specificity; D014197:Trees / Q000235:genetics* / Q000254:growth & development / Q000502:physiology*
keywords: Biotic interactions; Nothofagus pumilio; Patagonia; intraspecific aggregation; intraspecific facilitation; microsatellites; multi-stemmed trees; population genetics