Changes with altitude of the stand structure of temperate forests on Mount Norikura, central Japan

Changes in stand structure with altitude have been studied at ten sites between 800 and 2,500 m above sea level (a.s.l.) in temperate forests on Mount Norikura (36 degrees 06 ' N, 137 degrees 33 ' E, 3,026 m a.s.l.) in central Japan. Vegetation in this range of altitudes was roughly classified as a montane deciduous broad-leaved forest zone between 800 and 1,600 m a.s.l. and a subalpine coniferous forest zone between 1,600 and 2,500 m a.s.l. at the timberline. The frequency distribution of trunk height was an L-shaped pattern at 800 m a.s.l., changed to a flat pattern with increasing altitude up to 2,000 m a.s.l., but changed to an L-shaped pattern again from 2,000 to 2,500 m a.s.l. This change in frequency distribution of trunk height with altitude was related to the change in maximum trunk height with altitude. The maximum trunk height did not change with altitude between 800 and 2,000 m a.s.l. but it decreased markedly from 2,000 to 2,500 m a.s.l. Although mechanical damage to conifer trunks and branches was not observed between 800 and 2,000 m a.s.l., the proportion of damaged trees increased from 2,000 to 2,500 m a.s.l., suggesting that subalpine conifers cannot grow in height near the timberline because of mechanical damage. The increase in the number of small trees from 2,000 m a.s.l. to the timberline was therefore because of a less developed canopy structure, i.e. small trees can grow without shading by canopy trees. This study suggests that mechanical damage, probably because of strong winds in the winter, affects changes with altitude in regeneration and formation of the timberline.