Effects of harvesting of increasing intensities on genetic diversity and population structure of white spruce

Authors

  • Manphool S. Fageria,

    1. Faculty of Forestry and Environmental Management, Canadian, Genomics and Conservation Genetics Institute, University of New Brunswick, Fredericton, NB, Canada
    Current affiliation:
    1. Agriculture and Agri-Food Canada, Fredericton, NB, Canada
    Search for more papers by this author
  • Om P. Rajora

    Corresponding author
    1. Faculty of Forestry and Environmental Management, Canadian, Genomics and Conservation Genetics Institute, University of New Brunswick, Fredericton, NB, Canada
    • Correspondence

      Om P. Rajora, Faculty of Forestry and Environmental Management, Canadian, Genomics and Conservation Genetics Institute, University of New Brunswick, 28 Dineen Drive, Fredericton, NB E3B 5A3, Canada.

      Tel.: (506) 458 7477;

      fax: (506) 453 3538;

      e-mail: om.rajora@unb.ca

    Search for more papers by this author

Abstract

Forest harvesting of increasing intensities is expected to have intensifying impacts on the genetic diversity and population structure of postharvest naturally regenerated stands by affecting the magnitude of evolutionary processes, such as genetic drift, gene flow, mating system, and selection. We have tested this hypothesis for the first time by employing widely distributed boreal white spruce (Picea glauca) as a model and controlled, replicated experimental harvesting and regeneration experiment at the EMEND project site (http://www.emendproject.org). We used two approaches. First, genetic diversity and population structure of postharvest natural regeneration after five harvesting treatments (green tree retention of 75%, 50%, 20%, and 10%, and clearcut) were assessed and compared with those of the unharvested control (pristine preharvest old-growth) in two replicates each of conifer-dominated (CD) and mixed-wood (MW) forest, using 10 (six EST (expressed sequence tag) and four genomic) microsatellite markers. Second, genetic diversity and population structure of preharvest old-growth were compared with those of postharvest natural regeneration after five harvesting treatments in the same treatment blocks in one replicate each of CD and MW forests. Contrary to our expectations, genetic diversity, inbreeding levels, and population genetic structure were similar between unharvested control or preharvest old-growth and postharvest natural regeneration after five harvesting treatments, with clearcut showing no negative genetic impacts. The potential effects of genetic drift and inbreeding resulting from harvesting bottlenecks were counterbalanced by predominantly outcrossing mating system and high gene flow from the residual and/or surrounding white spruce. CD and MW forests responded similarly to harvesting of increasing intensities. Simulated data for 10, 50, and 100 microsatellite markers showed the same results as obtained empirically from 10 microsatellite markers. Similar patterns of genetic diversity and population structure were observed for EST and genomic microsatellites. In conclusion, harvesting of increasing intensities did not show any significant negative impact on genetic diversity, population structure, and evolutionary potential of white spruce in CD and MW forests. Our first of its kind of study addresses the broad central forest management question how forest harvesting and regeneration practices can best maintain genetic biodiversity and ecosystem integrity.

Ancillary