title: The importance of ecological constraints on the control of multi-species treeline dynamics in eastern Nunavik, Quebec.
abstract: OBJECTIVE
  Treelines are temperature-sensitive ecotones that should be able to expand in response to global warming; however, they are also controlled by ecological constraints. These constraints can create bottlenecks for tree regeneration, hindering treeline advances. Near Kangiqsualujjuaq (Nunavik, subarctic Québec), previous studies suggested successful recruitment of Larix laricina above the altitudinal treeline, while Picea mariana establishment remains scarce. We studied regeneration of both species to identify factors responsible for such contrasting responses. •
  
  
  METHODS
  We measured seeds and wings to evaluate species dispersal potential. We compared seed viability and tolerance to shrub leachates with germination trials. To evaluate seedbed preferences, we compared seedling occurrence on the different seedbeds with seedbed relative abundance in the field. •
  
  
  RESULTS
  Seed germination was similar between L. laricina and P. mariana, whereas dispersal potential was higher for the latter. Germination of P. mariana seeds was more strongly inhibited by shrub leachates than were L. laricina seeds. In the field, we found only a few Picea seedlings, but numerous seedlings of Larix had established disproportionally on several seedbeds. While Betula glandulosa, mosses, and Vaccinium uliginosim impeded Larix establishment, numerous seedlings were found on lichens, mineral soil, and liverworts. The low occurrence of suitable seedbeds for Picea, mainly mineral soil, could explain the seedling scarcity of this species. •
  
  
  CONCLUSIONS
  This study highlighted that allelopathy and unsuitable seedbeds could contribute to regeneration failure of P. mariana in eastern Nunavik and emphasizes the need to consider ecological preferences of species before predicting treeline expansion under a warmer climate.
authors.affiliation: Département de biologie and Centre d'études nordiques, Chaire de recherche nordique en écologie des perturbations, Université Laval, 1045 Av. De la Médecine, Québec, Québec, Canada, G1V 0A6.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Dufour-Tremblay
authors.forename: Laurent
authors.initials: L
authors.lastname: De Vriendt
authors.forename: Esther
authors.initials: E
authors.lastname: Lévesque
authors.forename: Stéphane
authors.initials: S
authors.lastname: Boudreau
mesh_terms: D000704:Analysis of Variance; D017753:Ecosystem; D005843:Geography; D018525:Germination; D010675:Pheromones / Q000378:metabolism; D011792:Quebec; D058614:Seed Dispersal / Q000502:physiology; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism; D012639:Seeds / Q000254:growth & development; D013045:Species Specificity; D014197:Trees / Q000502:physiology*
chemical_list: D010675:Pheromones