Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec

Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec Abstract. Human impact influences patterns of plant distribution and dominates disturbance dynamics in the agricultural landscape of Haut‐Saint‐Laurent, Québec. We investigated the influence of such impact on the dynamics of Thuja occidentalis in the hardwood forest of southern Québec. A bimodal species of either dry or wet habitats, T. occidentalis has successfully invaded mesic sites of the study area where, although generally considered a poor competitor, it persists as dense populations that seem to resist invasion by more tolerant species. As Acer saccharum is expected to be a dominant latesuccessional species under mesic conditions, we first evaluated the relative importance of abiotic and historical factors in the distribution of 34 T. occidentalis stands and 21 A. saccharum stands. We then classified 55 stands that include T. occidentalis and investigated the dynamic relationships between the species and its associates in 13 mixed mesic sites. Canonical correspondence analysis (CCA) of T. occidentalis and A. saccharum stands suggested that land use and drainage are the most important variables correlated with plant community composition. A partial CCA with drainage as the constraining variable showed that T. occidentalis stands were significantly associated to present or past use as pasture. Correspondence analysis of 55 stands where T. occidentalis is present produced a clear segregation between nearly monospecific stands and mixed communities, but the chosen environmental variables were not significant in explaining the vegetation gradient at this scale. In all mixed stands, Thuja occidentalis was most often associated with Ulmus americana, Acer rubrum, Betula populifolia, Fraxinus americana, A. saccharum, and Tsuga canadensis. Finally, size‐class ordination of 13 mixed mesic stands did not show convergence toward A. saccharum. Our results suggest that grazing has played a significant part in the appearance of T. occidentalis stands on mesic sites, whereas competition processes and landscape patterns possibly contribute to the maintenance of relatively persistent T. occidentalis stands in the landscape. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Vegetation Science Wiley

Dynamics of Thuja occidentalis in an agricultural landscape of southern Quebec

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Publisher
Wiley
Copyright
1995 IAVS ‐ the International Association of Vegetation Science
ISSN
1100-9233
eISSN
1654-1103
D.O.I.
10.2307/3236352
Publisher site
See Article on Publisher Site

Abstract

Abstract. Human impact influences patterns of plant distribution and dominates disturbance dynamics in the agricultural landscape of Haut‐Saint‐Laurent, Québec. We investigated the influence of such impact on the dynamics of Thuja occidentalis in the hardwood forest of southern Québec. A bimodal species of either dry or wet habitats, T. occidentalis has successfully invaded mesic sites of the study area where, although generally considered a poor competitor, it persists as dense populations that seem to resist invasion by more tolerant species. As Acer saccharum is expected to be a dominant latesuccessional species under mesic conditions, we first evaluated the relative importance of abiotic and historical factors in the distribution of 34 T. occidentalis stands and 21 A. saccharum stands. We then classified 55 stands that include T. occidentalis and investigated the dynamic relationships between the species and its associates in 13 mixed mesic sites. Canonical correspondence analysis (CCA) of T. occidentalis and A. saccharum stands suggested that land use and drainage are the most important variables correlated with plant community composition. A partial CCA with drainage as the constraining variable showed that T. occidentalis stands were significantly associated to present or past use as pasture. Correspondence analysis of 55 stands where T. occidentalis is present produced a clear segregation between nearly monospecific stands and mixed communities, but the chosen environmental variables were not significant in explaining the vegetation gradient at this scale. In all mixed stands, Thuja occidentalis was most often associated with Ulmus americana, Acer rubrum, Betula populifolia, Fraxinus americana, A. saccharum, and Tsuga canadensis. Finally, size‐class ordination of 13 mixed mesic stands did not show convergence toward A. saccharum. Our results suggest that grazing has played a significant part in the appearance of T. occidentalis stands on mesic sites, whereas competition processes and landscape patterns possibly contribute to the maintenance of relatively persistent T. occidentalis stands in the landscape.

Journal

Journal of Vegetation ScienceWiley

Published: Aug 1, 1995

References

  • Relations between the floristic composition of isolated young woods and their proximity to ancient woodland
    Dzwonko, Dzwonko
  • Riverine wetland vegetation: importance of small‐scale and large‐scale environmental variation
    Jean, Jean; Bouchard, Bouchard
  • Study of spatial components of forest cover using partial Mantel tests and path analysis
    Leduc, Leduc; Drapeau, Drapeau; Bergeron, Bergeron; Legendre, Legendre

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