ケニヤ山，Ｔｙｎｄａｌｌ氷河の後退過程と植生の遷移およびその立地条件

Abstract

The retreat process of Tyndall Glaciers and the vegetation were surveyed in Mount Kenya (5, 199m). Tyndall Glacier have retreated since early in this century and is retreating at an average rate of 2.88m/yr in the last 35 years. The first colonist of new till is Senecio keniophytum, which occurs at a distance of 18m from the 1992 ice-front. The speed of advance of this plant (1958-1984.2.65m/yr, 1984-1992: 2.13m/yr) is similar to the retreat rate of the glacier. The next species encountered is Arabis alpina, at 37m. This species advance at rate of 4.38m/yr (1958-1984), 4.63m/yr (1984-1992). Moss and lichen are next, at 70m and its speed of advance is 3.47m/yr. The species growing near ice-front of Tyndall Glacier advance in connection with retreat of the glacier. The species growing at distance over 100m from ice-front colonize irregularly independently of retreat process of the glacier.Till age and stability of land surface are important environment factors controlling vegetation pattern around Tyndall Glacier. Till age is affected by the glacial fluctuation. Stability of land surface is governed by particle-size of surface materials. Former climatic condition affects both glacial fluctuation and particle-size of surface material, and landform controls particle-size of surface material. On new till, plants is restrained from colonizing because of poor soil condition even if the slope is stable. Species growing on such slope are restricted to a few species, as Senecio keniophytum and so on, and vegetation coverage is low. On old till, environmental factors affecting both vegetation coverage and growing species are stability of land surface governed by particle-size of surface materials. On stable slope covered by big debris, vegetation coverage is high and such large plants as Senecio keniodendron, Lobelia telekii and so on are distributed. Slope covered by fine-rubble is unstable and shows low vegetation coverage by the effect of needle ice creep and solifluction because diurnal range of temperature is large.Although time of snow release is important environment factor governing alpine vegetation pattern in Japan because of heavy snow in winter, that is not very important factor for Mt.Kenya without enough snow. Wind is not very important factor because wind in Mt. Kenyais not strong. Environment of Mt. Kenya is similar to that of alpine wind-blown slope of high mountains in Japan, because both Mt. Kenya and alpine wind-blown slope in Japan don't have enough snow which work for repression of thermal fluctuation. Therefore, stability of land surface affected by particle-size of surface materials, which is important environment factor controlling vegetation pattern on Japanese alpine wind-blown slope, is important factor for alpine vegetation pattern in Mt. Kenya.