Changes in woody species beta diversity in forest communities reveal conservation priorities in the southeastern Qinghai-Tibet Plateau

Studying spatiotemporal changes in beta diversity and its drivers yields meaningful information to promote nature conservation. In this study, we surveyed tree and shrub species diversity in 107 historical plots in the southeastern Qinghai-Tibet Plateau. Then, we assessed the effects of environmental factors and plant functional and structural traits on the changes in beta diversity in all woody species. Our results showed that woody species beta diversity was rather stable over the past 40 years, and that stabilization of shrub species diversity played a key role. However, the beta diversity of trees homogenized due to a decrease in species replacement, so protecting tree species diversity should be prioritized. The changes of tree species beta diversity could be predominantly explained by the spatial distances of the samplings and the retained larger trees. In contrast, the change in shrub beta diversity was largely interpreted by decreased precipitation, increased tree canopy height, coverage, shrub leaf area, and dry matter content. Shrub species became more shade-tolerant and drought-tolerant. Because species replacement is the major component of beta diversity in this study, and the tree species replacement declined due to spatial limitation, we suggest to expand the protected areas to the locations with species complementary, rather than further lifting the protection strength within the existing protected areas, as an improvement in conserving the biodiversity of this important region.