Colonization of the polar willow Salix polaris on the early stage of succession after glacier retreat in the High Arctic, Ny-Ålesund, Svalbard

Authors

  • Takayuki Nakatsubo,

    Corresponding author
    1. Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan
      Takayuki Nakatsubo, Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan. E-mail: kuyakat@hiroshima-u.ac.jp
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  • Masaaki Fujiyoshi,

    1. School of Humanities and Culture, Tokai University, Kitakaname 1117, Hiratsuka, 259-1292, Japan
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  • Shinpei Yoshitake,

    1. Graduate School of Advanced Science and Engineering, Waseda University, 2-2, Wakamatsucho, Shinjuku-ku, Tokyo, 162-8480, Japan
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  • Hiroshi Koizumi,

    1. Faculty of Education and Integrated Arts and Sciences, Waseda University, 2-2, Wakamatsucho, Shinjuku-ku, Tokyo, 162-8480, Japan
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  • Masaki Uchida

    1. National Institute of Polar Research, 10-3, Midori-cho, Tachikawa City, Tokyo 190-8518, Japan
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Takayuki Nakatsubo, Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan. E-mail: kuyakat@hiroshima-u.ac.jp

Abstract

The polar willow (Salix polaris), predominant in the late successional stage in deglaciated areas of Ny-Ålesund, Svalbard, is rarely found in the early stage, when purple saxifrage (Saxifraga oppositifolia) dominates. To elucidate the pattern and the mechanism of successional change from the Saxifraga stage to the Salix stage, we examined the distribution pattern, size structure and habitat conditions of a colonizing Salix population in the seral stage where Salix was invading Saxifraga-dominated sites. The present distribution pattern and aerial photographs taken in the past suggest that Salix colonization at this site commenced within the last 70 years. We found 115 Salix individuals (22 male, 13 female and 80 unknown) in a 30 m × 30 m quadrat on the seral stage. Although the largest individual had a size of 2000 cm2 (length × maximum width), the majority (84%) of individuals were smaller than 100 cm2. The seedling size distribution, as inferred from the leaf scar number, indicated that annual recruitment was slight. Of the individuals observed about 75% had colonized bare ground; only four individuals grew within Saxifraga colonies. No significant difference was found in soil characteristics (water content, and carbon and nitrogen concentrations) between the seral stage and the earlier stage prior to colonization by Salix. These results suggest that difficulties in seed production, germination and/or seedling establishment of Salix, rather than soil formation by preceding species (Saxifraga), limits the early-stage colonization by Salix.

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