Different trajectories of floristic diversity in forested and open landscapes in China over the past 20,000 years.

Recently accelerating rate of biodiversity change has triggered exploring the trajectory of plant diversity change from a paleoecological perspective, but the discrepancy and cause of long-term diversity trends from distinct landscapes or ecosystems are largely unknown. Given this, the present study used 41 pollen records from China to investigate the trajectories of plant diversity changes in two distinct land-cover types, i.e., forest and open landscapes, over the past 20,000 years, and discussed the relative roles of long-term climate and anthropogenic land-use changes on plant diversity dynamics. Our results unraveled different trajectories of richness and evenness, and inconsistent relationships between richness and evenness in forest and open vegetation. We speculated that these discrepancies were caused by different mechanisms that structure the communities. At a general level, dispersal and migration processes were more important for diversity change in open vegetation, whereas species competition was more important in forest. Trends of temporal β diversity show a basically consistent pattern, indicating that the rates of change in diversity were comparable between the two landscapes on multi-millennium time scales. Anthropogenic land-use change controlled trajectories of diversity change in both landscapes during the Holocene but its effects have not yet overridden the cumulative impact of climate change since the last deglaciation. Our study unraveled that plant diversity dynamics over the past 20,000 years was primarily a result of the changes in compositional turnover, which emphasizes the need for a regional approach to conservation planning that focuses not only on species losses but also on species replacements.