Inbreeding depression at the sapling stage and its genetic consequences in a population of the outcrossing dominant tree species, Castanopsis sieboldii

Highly frequent pollination at short distances combined with spatial genetic structure (SGS) among reproductive individuals, as observed in populations of many forest tree species, may lead to highly frequent pollinations between genetically related individuals located close to each other. This could increase frequencies of biparental inbreeding and strengthen the degree of SGS across generations. However, the degree of SGS observed in forest tree populations is not usually strong, suggesting that such processes are restricted by other factors, which may include inbreeding depression. To test this hypothesis, we examined inbreeding depression in Castanopsis sieboldii saplings in a population known to have significant SGS and high frequencies of short-distance pollination. We determined genotypes at eight microsatellite loci of 125 adult trees and 899 saplings in a 4-ha plot. The neighborhood model approach, assuming an exponential power function, showed highly frequent pollination at sh...