The spatial genetic pattern of Castanopsis chinensis in a large forest plot with complex topography

Topography is an important environmental feature that affects the spatial genetic structures of plant species. However, its influence on such structures at small spatial scales has hardly been investigated for forest tree species even though many of them are located in mountains with complex topographic features. Here we report the genetic structures of a pioneer species, Castanopsis chinensis (Fagaceae), in a 20-ha forest plot in Dinghushan in lower subtropical China, which has complex topographic features, such as valleys and ridges. C. chinensis typically undergoes wind pollination, but its seeds are dispersed by gravity and animals. Therefore, the mechanisms of transportation of its seeds may result in topography-dependent genetic structures, whereas wind-mediated pollen flow of C. chinensis may reduce such structures through counteracting the influence of topography. Our results indicate that most of the genetic patterns in C. chinensis in our study plot were attributable to wind-mediated pollen flow. However, we also found both seed and pollen flows could be impeded by ridges, causing some varied genetic patterns even between locations separated by only small distances. We observed that owing to topographic positions where they grew, the 13 old individuals that were probably the oldest in the southeast corner of the plot had not made major genetic contributions to the young individuals that had recently colonised previously clear-cut land in the rest of the plot. Therefore, our results indicate that we should consider both species life-history traits and topography when studying the genetic structures of plant populations in order to design sound conservation and management programs for the areas with complex topography.