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Biotic disturbance in expanding subarctic forests along the eastern coast of Hudson Bay

Authors

  • Marco Caccianiga,

    1. NSERC Northern Research Chair, Centre d’études nordiques, Université Laval, Québec, Canada G1K 7P4;
    2. Present address: Dipartimento di Biologia, Sezione di Botanica Sistematica, Università di Milano, 20133 Milano, Italy
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  • Serge Payette,

    1. NSERC Northern Research Chair, Centre d’études nordiques, Université Laval, Québec, Canada G1K 7P4;
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  • Louise Filion

    1. Département de géographie and Centre d’études nordiques, Université Laval, Québec, Canada G1K 7P4;
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Author for correspondence:
Marco Caccianiga
Tel: +39 0250314848
Fax: +39 0250314840.
Email: marco.caccianiga@unimi.it

Summary

  • • The past and present occurrence of insect disturbance on white spruce (Picea glauca) trees was evaluated at their northern range limit on the eastern coast of Hudson Bay, and its effects on tree growth and population dynamics studied.
  • • Three sites were sampled along an altitudinal gradient. Ring-width chronologies and stem analysis were used to evaluate tree growth. The occurrence of holes in the bark, of resin pockets and blue-stain fungi, and ring-width evidence for growth releases were used to assess the impact of bark beetle.
  • • The white spruce population was established at these sites in the 17th century. Since their establishment, the spruce trees have developed a tree growth form, except at the uppermost site, where severe growth suppression occurred in the 19th century. Bark beetle and blue-stain fungi occurred with different timing and intensity. Their highest occurrence, associated with high mortality rates, was at the lowest site in the late 20th century. In the uppermost sites, biotic disturbance has occurred since the 18th century, associated with evidence for mechanical disturbance.
  • • The simultaneous arrival of white spruce in the area resulted in a synchronous onset of spruce beetle activity driven by tree ageing. Unfavourable climatic conditions affected tree growth severely in the most exposed sites.

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