Importance of landscape features and fire refuges on genetic diversity of Thuya occidentalis L., in boreal fire dominated landscapes
The unburned forest remnants of boreal mixed-woods, also known as fire residuals, are essential in providing habitats for disturbance-sensitive species and function as the main source of recolonization of disturbed sites. Forest remnants have been identified as historical or potential reservoirs of genetic diversity in several tree species in fire-prone landscapes. In this study, we investigate the genetic diversity of eastern white cedar (EWC, Thuya occidentalis L.), in forest sites that were affected by different fire regimes. The study area is located in northwestern Quebec, in the Lake Duparquet Research and Teaching Forest (79°10′W–48°30′N). We used 18 polymorphic microsatellite loci to investigate the genetic diversity of eastern white cedar, in forest sites where the fire regime history has been reconstructed to examine the importance of the temporal and spatial continuity of the forest on the genetic diversity of EWC. Three types of landscapes, including; islands within a large lake, fragmented fire refuges (forest patches) and non-fragmented mainland forests were studied. Our results revealed a source-sink dynamic associated with a high level of gene flow. Two of the mainland sites served as the main source of migrants. The level of gene flow in island sites was sufficiently high to counteract the effect of isolation. The fire refuges showed the lowest allelic richness, the highest population differentiation and the fewest number of private alleles. The mean fire-free intervals are much longer in fire-refuges causing environmental isolation through time and higher genetic differentiation. The conservation of large mainland sites should be given careful attention because they maintained high genetic diversity and function as the main source of gene flow. Fire refuges have an intrinsic conservation value in landscapes that are affected by spatially heterogeneous fires because they are important for population persistence through disturbances.
KeywordsBoreal old growth forest Conservation genetics Fire-prone landscape Fire refuges Forest remnant Fire residuals Gene flow Lake-islands landscape
This work is part of the PhD thesis of H. X. We would like to acknowledge M. H. Longpré and D. Charron for logistical support and Y. Zhou for assistance in the lab. Special thanks go to the industrial supervisors from the company Tembec. This research was supported by an Industrial Innovation Doctoral Scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC), a BMP innovation doctoral scholarship from the Fonds de recherché du Québec- Natures et technologies (FQRNT) and Tembec, and a scholarship from the Forêt d’enseignement et de recherche du lac Duparquet (FERLD) to H. X. This research was also funded by a NSERC strategic grant (STPGP 336871) to F. T.
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