Contrasting relationships between species diversity and genetic diversity in natural and disturbed forest tree communities

This study aimed to reveal speciesgenetic diversity correlations (SGDCs) and their underlying mechanisms in natural and disturbed forests. A community survey and molecular analyses were carried out to compare species diversity (SD), the genetic diversity of the dominant tree species Euptelea pleiospermum (GD), the altitudinal patterns of SD and GD, SGDC, genetic differentiation (FST), community divergence (FST-C), effective population size (Ne), and recent migration rate between mountain riparian forests along the Yandu (natural) and Nan (disturbed) rivers. In natural forests, both SD and GD showed a unimodal altitudinal pattern and GD was positively correlated with SD, whereas a unimodal pattern and positive SGDC were not found in the disturbed forests. SD and FST at the natural sites were higher than those at the disturbed sites. However, there were no significant differences in GD, FST-C, Ne or recent migration rate between the natural and disturbed sites. A correlation between the patterns of SD and GD along a geographical gradient (e.g. altitude) is an important driver of positive SGDC. The absence of positive SGDC in the disturbed forests may result from reduced SD but unaffected GD, indicating nonparallel changes in SD and GD. This study furthermore cautions against generalizations about changes in SD and GD following disturbance.