Survival and Growth of Two Coexisting Evergreen Oak Species after Germination under Different Light Conditions

Abstract

The germination, survivorship, and growth of seedlings of Castanopsis cuspidata and Quercus gilva, both evergreen oaks in the evergreen broad-leaved forests of southwestern Japan, were observed over a 3-yr period under light conditions ranging from full sunlight to 2% of full sunlight. My purpose was to determine how light condition affects the establishment of these species and the eventual compositions of regional forest stands. At the end of the first growing season many seedlings did not have aboveground shoots, irrespective of the light conditions. These shootless seedlings form two groups: either shoots perished because of the hot and dry summer or shoots did not emerge at all. However, many of the shootless seedlings of C. cuspidata produced a shoot in the following year. Despite having smaller acorns and more shootless seedlings, C. cuspidata survived the hot and dry summer as well as Q. gilva did. The low shoot/root mass ratio of established C. cuspidata seedings at the end of the first season may be a key to survival. Although shootless seedlings were smaller than ordinary seedlings, by year 3 growth rates of both were similar, suggesting that the shootless seedlings contribute to regeneration. By year 3 mortality of both species was low and similar, except in 2% full sunlight where Q. gilva had greater survival. At the end of three growing seasons, C. cuspidata reached Q. gilva in height and biomass growth under bright conditions, and C. cuspidata had greater shoot/root mass ratio and smaller specific leaf area compared with Q. gilva.