Micro-landform Structure and Tree Distribution in Subalpine Riparian Area of V-shaped Valley, Minami Alps, Central Japan

Riparian areas are unique habitats that contribute to biodiversity, so they have been focused on in many regions; however, subalpine riparian forests have hardly been examined in Japan. We investigated the micro-landform structure and spatial pattern of tree distributions in a V-shaped valley at 2,000–2,200 m a.s.l. in the Minami Alps, central Japan, using a 0.42 ha core-plot and 16 belt-transects set in a headwater area of Norogawa River. As riparian topographical components, channel, floodplain, scarp of terrace and terrace were detected, which were arranged roughly from lower to higher elevations from streams, as well as mountain slope as a micro-landform unit outside the riparian area. Single-layered floodplain, conspicuous terrace segments and the probable lack of a lower sideslope were identified as features that differ from those found in previous studies on other climatic/largescale geomorphological conditions. The distribution of deciduous species was biased to lower elevations, with the representatives Salix cardiophylla var. urbaniana on floodplains and Alnus matsumurae on scarps of terraces. These micro-landform units were recognized as a riparian zone in terms of vegetation. Meanwhile, climatic climax evergreen conifers, mainly Abies veitchii, Tsuga diversifolia and A. mariesii, dominated not only mountain slopes but also terraces, indicating that terraces are upland areas in terms of their vegetation. A much smaller area, low species diversity and an assumed direct succession from pioneer to climax phase, because of poor long-lived riparian species capable of forming a midor late successional phase, were properties differing from those found in previous studies on other climatic/geomorphological conditions.