Influence of micro-landforms on forest structure, tree death and recruitment in a Japanese temperate mixed forest

The micro-landform unit system offers an effective way of analyzing vegetation-geomorphology relationships at a 10-m scale in areas such as the hilly regions of Japan. We analyzed relationships between micro-landforms and tree population parameters over a 9-year interval to elucidate the influence of geomorphic processes on vegetation dynamics. A 2.16-ha permanent plot was established in a temperate mixed forest. Each 5 m x 5 m quadrat within this plot was classified according to six types of micro-landform units: (i) crest slope (CS); (ii) upper sideslope (US); (iii) head hollow (HH); (iv) lower sideslope (LS); (v) foot slope (FS); and (vi) river bed (RB). All living trees larger than 10 cm in diameter at breast height (d.b.h.) were identified, mapped and marked in 1989 and resurveyed in 1998. Almost all of the 23 common tree species persisted in their own core habitats (i.e. the micro-landforms) between the two surveys. The species distribution in both surveys showed that the six micro-landforms could be combined into two larger groups: upper and lower hillslope areas. The upper hillslope area had higher tree densities and larger basal areas than the lower hillslope area. It is possible that these differences result from the longer lifespans of trees on the upper hillslope area rather than from differences in mortality and recruitment rates. In addition, the different ways in which trees die in the different micro-landform units may affect the regeneration process in hilly regions through different gap formation. The effects of different geomorphic processes are reflected in the lifespans of the trees and may result in different forest structure and dynamics among microland form units.