Effects of sprouting and canopy states on the structure and dynamics of a Castanopsis cuspidata var. sieboldii sapling population in an old-growth evergreen broad-leaved forest

We examined the structure and dynamics, over 3 years (mortality, recruitment, stem growth and sprout formation), of Castanopsis cuspidata var. sieboldii (nomenclature follows Ohwi and Kitagawa, 1983) saplings in relation to canopy states such as old gap (canopy gap maintained), closed gap (canopy gap changed to closed canopy), new gap (closed canopy changed to canopy gap) and closed canopy (closed canopy maintained). We used these data to evaluate how forming or having sprouted shoots affected the maintenance of a sapling population in an old-growth evergreen broad-leaved forest, at Tatera Forest Reserve, southwestern Japan. Canopy trees were distributed randomly in the 1 ha study plot, whereas saplings were clumped. During the study, annual mortality and recruitment rates of saplings were 7.5 and 8.5%, respectively. These rates fluctuated within each year. Mortality was highest at closed-canopy sites and lowest at new-gap sites, although the difference was not significant. On the other hand, recruitment was significantly highest at closed-canopy sites and significantly lowest at new-gap sites. The relative growth rate of stem length was significantly highest at new-gap sites and significantly lowest at closed-gap sites. Mortality rate did not differ significantly between saplings with or without sprouted shoots, but sprout formation and stem replacement did. Saplings without sprouted shoots grew more in stem length than did those with sprouted shoots. The presence of sprouted shoots had little effect on sapling recruitment from the understory to upper layers, but it did contribute to declining sapling mortality and to maintaining sapling population size under closed canopies. (C) 2003 Published by Elsevier Science B.V.