Plant Community Dynamics and Microtopography Close to the Tree Line on the Northwestern Slope of Mt. Fuji, Central Japan

We studied the relationship between slope processes and plant community structure on the northwestern side of Mt. Fuji. This slope has a stepped microtopography between 2700 and 2950 meters above sea level, with a particularly well-defined structure between 2800 and 2850 m. This stepped microtopography is almost certainly caused by periglacial process and acts as a foundation for the development of islands of plant communities. These communities are concentrated on riser sections of the steps, with virtually no growth on flat, terraced areas. Ground temperature monitoring and paint-line exposure experiments showed that the gravel is unstable on the terraces but stable on the risers. It is proposed that the vegetation distribution is determined by the stability of the surface materials. In addition, variation in snow depth by step component should have an effect on the vegetation distribution. The plant community composition is diverse on the upper slopes; Salix reinii is predominant and mosses are also prominent. The lower slopes are dominated by tree species, including Larix kaempferi and Betula ermanii. L. kaempferi had fewer annual rings with increasing slope elevation, suggesting that populations were established at different times at different altitudes. We predict that primary succession at the tree line has moved to progressively higher elevations on the northwestern slope of Mt. Fuji using the stepped microtopography as a foundation. key words plant establishment, slope process, stepped microtopography, soil temperature, freeze-thaw cycle, grain size, matrix