Response of riparian plant community to landscape matrix differs by taxonomic and functional diversity: Implications for the planning of riparian landscapes regulated by dams

Local plant communities are embedded within the landscape matrix, and thus, diversity of these communities is largely determined by the spatial pattern of surrounding land-use. However, it is not yet clear how taxonomic and functional diversity within riparian plant communities respond differently to the landscape matrix at different scales, and whether and how these landscape-scale responses can be shaped by flooding conditions in the riparian landscape. This study is based upon field surveys of riparian plant communities in a total of 136 quadrats exposed to two different levels of flooding intensity along the reservoir formed by the Three Gorges Dam (TGD). We investigated the relationship between plant diversity of riparian communities and the surrounding landscape at different scales, which examined how the diversity, in terms of both plant taxonomy and functional traits, was affected by the landscape matrix at 15 different spatial scales ranging from 200 m to 3000 m in increments of 200 m around each sampling site. Furthermore, the community diversity in response to the landscape matrix under different levels of flooding intensity was also examined. Our findings suggested that trait-based functional diversity was more closely related to the landscape matrix at all 15 scales examined, compared to taxon-based diversity. The dispersal trait was found to be more susceptible to landscape connectivity across the matrix. Further, both types of diversity responded more strongly to landscape configurational metrics than compositional metrics. In addition, we observed that, in the communities exposed to high flooding intensity, the two types of diversity tended to have more consistent responses to the landscape matrix compared to those exposed to low flooding intensity. We concluded that while the landscape matrix had different effects on taxonomic and functional diversity, the high flooding intensity could lessen their differences in the riparian landscape. Our findings revealed that the robust local environmental filtering process, which affects the diversity of riparian communities, could lead to both diversity components exhibiting similar responses to the landscape matrix in riparian landscapes.