Landscape connectivity and network construction of riparian vegetation in typical reach of the middle and lower reaches of Yellow River

Riparian ecosystems form the linkages and exchange zones of matter, energy and information between aquatic and terrestrial ecosystems.The characteristics of such zones significantly influence integrated landscape ecosystem functions from land to riparian regions.Riparian vegetation as an important component of riparian ecosystem, is the basis of the formation and maintenance of riparian buffer zone ecosystem services.However, riparian vegetation has now been widely recognized as fragile and sensitive system requiring conservation as it undergoes strong disturbances and great alteration by anthropogenic activities globally.Conservation activities have largely focused on the restoration or creation of natural areas to facilitate the movement of organisms.This is often based on reliable measurement of landscape connectivity and patch importance.In this study, a typical riparian buffer zone in the middle and lower reaches of Yellow River was analyzed for landscape connectivity and importance of riparian vegetation in 2003, 2009 and 2015 using remote sensing, landscape connectivity indexes, patch importance evaluation and corridor-network analysis.Also the study constructed a riparian vegetation corridor-network in order to provide support for maintaining biodiversity in riparian buffer zones in the middle and lower reaches of Yellow River.The results indicated that landscape connectivity of riparian vegetation increased both from 2003 to 2015 and with increasing threshold distance.Thus the number of links (NL) and the number of the largest component (NLC) of vegetation patches increased from 2003 to 2015 and they increased with increasing threshold distance.However, the number of components decreased from 2003 to 2015 and with increasing threshold distance.The integral index of connectivity (IIC) and the probability of connectivity (PC) increased with increasing threshold distance.Under different threshold distances, the importance value increased with increasing patch area.Thus with increasing threshold distance, the importance value of small patches (0-5 hm²) increased gradually, that of middle patches (5-10 hm²) initially increased and then decreased, while those of large patches ( > 10 hm²) decreased gradually.When the threshold distance was more than 1 000 m, the importance values of small, middle and large patches became stable, indicating that 1 000 m was the optimal threshold distance for the analysis of landscape connectivity in the study area.Ultimately, the corridor-network analysis proved to be important reference for the construction of riparian vegetation corridor-network. It sim-ultaneously considered important ecological nodes, ditches and road corridors in the study area as the established vegetation network system had high corridor node number, network closure and connection degree.In addition, riparian vegetation corridor-network construction should not only prioritize the connection between large patches, but also emphasize the stepping-stone role of small and middle patches between the large patches.