| Riparian zone is a vulnerable ecosystem with the most comprehensive functions. It has irreplaceable functions and research value. According to the research, species richness of plant community in riparian zone is generally higher than that in any area far away from riparian zone. Therefore, in the riparian zone of ecological system has important realistic and potential value to increase the origin of the plant and animal species, and strengthen biodiversity and ecosystem productivity.In recent years, the human is more and more strong desire to nature because of the rapid development of social productivity, has more and more influence on nature. As a result, riparian zone and its vegetation are destroyed, which seriously threatens the biological diversity in riparian zone.It is indispensable to research species diversity of riparian zone for maintaining integrity of ecosystem in riparian zone.In this study, Braun-Blanquet cover-abundance scale was used to investigate the characteristics of plant community diversity of typical reach the riparian zone in the middle and lower reaches of the Yellow River, and herbaceous plants diversity and the relationship between the environmental factors are discussed in this paper; The classification maps of landscapes in riparian zone in 2003, 2009 and 2015 were selected to calculate the number of linkage(NL) among the patches, The scenery in the number of components(NC), the overall connectivity index(IIC), the probability of connection(PC) and the important value of patches(dI) of woodland and grassland, and connectivity analysis of the dynamic changes of vegetation landscape research field in the past 12 years. To reduce landscape fragmentation and increase connectivity, four vegetation networks were built through analysis on the ecological nodes and ecological corridors in the landscape in riparian zone. Contrastive analysis was carried out by using vegetation corridor structure indexes and network structure indexes. The corridor structure was analyzed by using the following four indexes(ecological node index, ecological corridor index, ecological corridor length and ecological corridor density), while the network structure was analyzed by using four indexes of central level, dotted line rate, network connectivity and cost ratio, thus obtaining a vegetation network planning scheme which was favorable for biological diversity and ecological landscape. Suggestions regarding optimizing vegetation pattern were proposed, hoping to provide some theoretical reference for protecting the diversity of plant species in riparian zone. The research results indicated the follows:(1)There are 36 families, 78 genera, 86 species in total in the 52 community quadrats investigated for the typical arrived in riparian zone in the middle and lower reaches of the Yellow River, community species composition is rather rich, but dominant species is not obvious. In single community quadrat, species composition is simple, obvious difference is existed for species composition and diversity between different quadrats, besides, diversity of species is relatively low for middle streams area where is disturbed seriously, Shows a typical riparian zone plant species diversity in the middle and lower reaches of the Yellow River is the serious influence habitat destruction caused by human disturbance. Redundancy analysis(RDA) shows that altitude and distance to center line of river are significant influencing factors for plant diversity of riparian In the middle and lower reaches of the Yellow River.(2)The area and quantity of vegetation patches were increasing in 2003, 2009 and 2015, with the quantity of patches increasing from 922 in 2003 to 1446 in 2015 in the past 12 years. The quantity and area of patches were large in 2009 and 2015, when the landscape structure was stable with sound landscape connectivity, and important value of patches(dI) was in direct proportion to patch area. In this paper, analysis was carried out on the vegetation in riparian zone from 3 perspectives. By using landscape connectivity, researchers concluded that the appropriate distance threshold was 1000 m~2000 m when carrying out ecological security assessment, landscape structure adjustment, ecological planning and urban construction. When the distance threshold was 1000 m and 2000 m, the number of components(NC) reduced significantly, the quantity of patches with maximum number of components increased, landscape connectivity also increased significantly, and the importance of small and medium-sized patches was highlighted, which was related to the distribution features of the vegetation patches in the research area. The patch in the research area distributed in small areas, and the vegetation distributed in sheets. With large distance, sheets of large patches distributed separately. Patches in the research field distribution in a small area, and vegetation distribution table.Big distance, table big patch distribution respectively.Banks of the river with a patch in the middle and lower reaches of the Yellow River is affected by human activities, as well as the natural rivers and ditches, the main reason for the separation of human interference in the zone distribution of the vegetation. In the research area, there were more vegetation patches where human activities occurred frequently and where there were more residents. The landscape connectivity was constantly increasing in 2003, 2009 and 2015, which proved that people in the research area increased their awareness of environmental protection. On the other hand, many dams were constructed in the research area. The river was hindered by the dams, which affected the natural spreading approach of the vegetation along the bank. As a result, the vegetation along the bank couldn't spread effectively, thus affecting the distribution and community composition of vegetation in riparian zone.(3)According to the network nodes of vegetation and corridor distribution in riparian zone, they were classified into important ecological nodes and general ecological nodes, general ecological patches and important ecological patches after sufficiently learning and analyzing the main function and surrounding land of each node and corridor. Four vegetation network schemes were constructed. Contrastive analysis was carried out by using vegetation corridor structure indexes and network structure indexes. The corridor structure was analyzed by using four indexes(ecological node index, ecological corridor index, ecological corridor length and ecological corridor density), which concluded that the corridor of vegetation network scheme III and vegetation network scheme IV were the most complicated. The network structure was analyzed by using four indexes(central level index ?, index of dotted line rate ?, index of network connectivity r and cost ratio), which concluded that central level index ? of vegetation network scheme IV was 0.59. This result showed that there were the most loops in scheme IV. The index of dotted line rate ? of scheme IV was the largest, 2.14, which reflected that its corridor connectivity was the largest. The network connectivity r of scheme IV was 0.72, the largest of the four schemes, which indicated that it had the best network connectivity. The cost ratio of network III was small, 0.49, which indicated that it was comparatively easy to construct and implement it. Through comprehensive comparison on corridor index and structure index, vegetation network IV was proved to be an optimal scheme of vegetation in riparian zone. |
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