Abstract
Although the Janzen-Connell model recognizes high level of predation as
the main factor influencing propagule survival close to parent trees,
acorns of white oak species germinate immediately after seed fall and
might serve as a mechanism to escape this predation. In this study, we
investigated the seedling establishment, growth, mortality and
recruitment of two co-occurring oak species Quercus variabilis and Q.
aliena as a function of distances to conspecific adults, to examine if
Janzen-Connell effects necessarily result in Janzen-Connell pattern in
temperate white oak forests. Our results showed that the survivorship of
1-year-old seedlings of the two white oak species was negatively
correlated with the distances from the parent trees. This pattern of
seedling survivorship can largely be explained by rapid germination of
white oak acorns in autumn and/or the high regeneration capacity of the
robust taproots even after the cotyledons are predated. Recruitment
possibility indicated by the 2-year-old seedlings, however, showed an
exact compensation pattern, generally reflecting the interaction between
high level of seedling establishment and host-specific herbivores under
the parent trees. Our results provide evidence that rapid autumn
germination of acorns and high regeneration capacity of taproots limit
the occurrence of Janzen-Connell effects on seedling survival close to
parent trees of white oaks in temperate forests.