Classification and comparison of oak dominated forests on the eroded fan remnant at the foot of Yatsugatake volcano, central Japan

In order to evaluate the landform-mediated differences in the regeneration of oak (Quercus crispula), we compared the composition and diameter distribution of 77 stands on an eroded fan remnant at the foot of Yatsugatake volcano in central Japan. In total seven site units were classified on the basis of the combination of the vegetation, topography and soil data. Overall, the patterns of compositional change were strongly related to the topographic and edaphic differences among fluvial landforms. Oak dominated the units on the older-fan surfaces: mounds, depressions, rock outcrops and side slopes, but it was rare in the units on the valley floor: stream terraces, natural levees of coarse rock fragments and seeps. The units on the older-fan surfaces, except for rock outcrops, were covered by fine fertile organic soils (Andisols), while coarser fluvial deposits covered the units on the valley floors. Oak was most abundant on the mounds followed by the depressions, rock outcrops and side slopes. Oak sapling density was low even in oak stands, and it was very low on well-drained sites with high abundances of shade-tolerant trees. Sapling and seedling abundance of these shade-tolerant tree species were high on side slopes and rock outcrops but low on Andisols with thick humus layer and in areas with dense dwarf bamboo (Sasa nipponica) coverage. Under the current conditions of reduced disturbance frequency, we predict that Q. crispula will be replaced by shade-tolerant tree species, especially on side slopes and rocky outcrops.