Structure and dynamics of Japanese beech (Fagus japonica Maxim.) stools and sprouts in the regeneration of the natural forests

Abstract

Structure and spatial distribution of stools and root-collar sprouts of Japanese beech (Fagus japonica) were studied to clarify the regeneration processes of the stool and the population, and the ecological importance of this stool formation in five quadrats of the natural forests with different forest floor vegetation on the Pacific side of Japan. F. japonica dominates in the canopy of each quadrat. Most of sprouts formed a circle around the root-collar and lowest parts of the parent stems of the stool with the youngest sprouts at the periphery. The regeneration by seedlings was slight especially on the forest floor vegetation of the dwarf bamboo Sasa. The variety of size structure of stems and the existence of dead traces and/or dead center in each stool, the apparent difference in stool size, and the aggregations of stools in the forests suggest that stool expansion and long persistence of the stool at a given location may contribute to compensate for the scarcity of regeneration by seedlings inhibited by dwarf bamboo, and by the other shrubs and herbs.

Response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps

“…Main medium sized tree and shrub species were Acer Shirasawanum, A. distylum and Fraxinus lanuginosa in Okukinu and Prunus grayana, Meliosma myriantha and Carpinus cordata in Takahara, respectively. The undergrowth was dominated by 0.6 m tall dwarf bamboo, Sasa nipponica, which covered 43% of the area in Okukinu and 88% in Takahara (Ohkubo 1992).…”

“…grosseserrata and some Acer species. Throughout its geographic distribution range, E japonica stems naturally form vigorous sprouts from the root-collar (Tohyama 1965;Ohkubo et al 1988;Peters & Ohkubo 1990;Ohkubo 1992). The sprouts are connected with each other at their epigeal parts and form a permanent base of a individual tree (here we call 'stool').…”

“…Thus a stool becomes a cluster of stems that reach into the canopy. These stems may become separated stools (Ohkubo 1992). Within a F. japonica stool, one or more of these sprouts may replace a canopy stem that has died.…”

Age structure and dynamics of Cercidiphyllum japonicum sprouts based on growth ring analysis

“…Sprouts under a canopy of Fagus japonica Maxim. continue to grow after the death of the main stem (Peter and Ohkubo, 1990), and the stand expands and disconnects (Ohkubo, 1992). Ohkubo et al (1996) suggested that these sprouts play a role in 'sprout banks', analogous to seedling banks (Bellingham et al, 1994).…”

“…On the other hand, in the absence of human activities, tree species that produce many sprouts are mostly found in areas that experience disturbances, such as heavy snowfall (Okitsu, 1991;Tanimoto, 1993), coastal winds (Ito, 1993;Ito and Gyokusen, 1996), and steep slopes (Sakai et al, 1995), where conditions are generally too severe for seedlings to regenerate. Therefore, sprouting likely compensates for sparse seedling regeneration (Hara, 1987;Ohkubo, 1992;Kruger et al, 1997). Even in stable forests, sprouting plays an important role in the maintenance of forest vegetation by repairing the forest canopy after gap formation (Koop, 1987;Ohkubo et al, 1988Ohkubo et al, , 1996Peter and Ohkubo, 1990).…”