NICHE PARTITIONING OF PLANT TAXA ASSOCIATED WITH GEOTHERMAL VENTS AT WAKOTO, HOKKAIDO, JAPAN

Abstract

  To examine interaction among species in a stressed community, vegetation samples were taken at the geothermal area of Wakoto, Hokkaido, Japan. Only 17 macrophytic species occurred, and these could easily be separated into niches based on soil pH, surface and root zone temperatures, moisture, and distance from vent. Competition among bryophytes and between bryophytes and vascular plants was evidenced in bimodal distributions of the species along temperature, moisture, and pH gradients. The tall grass Miscanthus sinensis occupied 100% coverage in the pH range of 5.0 to 5.5, causing a bimodal pH distribution in the liverwort Jungermannia infasca and the short grass Fimbristylis dichotoma. A similar bimodal distribution in the liverwort Odontoschisma denudatum may result from the abundance of the moss Hypnum plumaeforme at the mid soil moisture range. Vascular plants were restricted to the lower end of the soil temperature range, whereas soils with higher temperatures were solely occupied by bryophytes and Cyanobacteria. This provides evidence for competition between bryophytes and with vascular plants, and documents the ability of bryophytes to occupy areas unsuitable for rooted vascular plants. It also supports the concept that bryophytes have a wider range of tolerance than do most vascular plants, but that they are not good competitors with them for physical space.