Study On Riparian Plant Of Mountain River

Riparian plant community is an important part of riparian ecosystem, which comprises a broad assemblage of diverse forms, various vegetation types. The riparian ecosystem is an important core in the wetland ecosystem of river, in which the riparian plant community contributes to the production and creation, and determines many significant ecological processes in the river ecosystem. Study on riparian plant community not only helps deepen the theory of riparian ecosystem, but also has important vital meanings and application value of protecting the river environment and biodiversity.Plant communities in riparian zone are influenced by spatial scale, different types and degrees of natural disturbance and human disturbance. With an eye to forward field of international riparian ecological research, character of riparian plant communities, the relations between riparian plant communities and hydropower development, impoundment of Three Gorges Reservoir (TGR), and the responses of riparian plant communities to different disturbance were studied at different spatial scales in Pengxihe River watershed, based on the knowledge of'3S', geography, vegetation ecology, environmental science. Major conclusions of this research are as follows:1. Study on spatial pattern of river hierarchy could be help to river development, conservation and management. The structure of watershed and streams of Pengxihe River were modeled with 1:10 000 topographic map under ArcGIS 9.0. The spatial distribution of different order was studied with the elevation, slope and NDVI data. The results showed that:(1) A seven hierarchy established in Pengxihe watershed, with first order streams contributing up to 50% of the watershed. (2)Altitude change range, average elevation, slope change range and average slope decreased with steam order. (3) NDVI index increased with the stream order, which meant the vegetation around lower order's stream was better than that of higher order's ones. (4) Combined the relation of height, slope, NDVI index and hierarchy of river with field investigation, grade 1 to 3 were considered to be XI which, in comparison with HE (grade 4 to 7). Synthesize the hierarchy of streams and NDVI, the stream orders well reflected the disturbance degree and disturbance types well, from weak to strong, from natural to human.2. Based on field observation, the species composition, life-form and flora were studied. The results showed: (1) There were 859 species of riparian zone, which belongs to 470 genera and 151 families, in Pengxihe River. Among them there were 25 species, 31 genera and 23 families of pteridophyte, 14 species, 11 genera and 7 families of gymnosperm, and 786 species, 428 genera and 151 families of angiosperm. Onotypicand families, oligotypic families, monotypic genus, onotypic and oligotypic genus took larger proportion in the composition of the families and genuses. This indicated the severe condition and the unique of plants in riparian zone. (2) Herb species were the dominant groups, possessed 62.87% of the total species, with 95 trees and 224 shrubs. A total of 227 species of vascular plants were recorded in the water-level-fluctuation zone, among which there were 107 hygrophyte, with 97 land herbs, 6 trees and 17 shrubs. (3) The floristic analysis showed the geographical element was complex. For family, cosmopolitan, tropic to temperate types were 34.38%,25.78%,12.50% of the total families, respectively. For genus, there were 200 genera belonging to temperature type, 178 genera belonging to tropic type, which showed the transitional characteristics of riparian plant. Composition of plant community fully reflected the transitional characteristics from subtropical to north subtropical zone in Pengxihe watershed. Richness of endemic or relic plants indicated the old-growth and relictual characteristics of riparian plant communities.3. In order to know the effect of stream orders on riparian plants, a total of 34 sampling sites were conducted along the Donghe River continuum from 1st order to 6th order in the upstream of Pengxihe Watershed. The results showed: (1) Environmental factors (altitude, riparian slope, riparian width, river width, substrate heterogeneity and human disturbance) among stream orders had significant differences. (2) Among stream orders, species richness showed remarked difference. Total species richness, shrub species richness, herb species richness and herb quadrat species richness rose firstly and dropped afterwards; tree species richness and shrub quadrat species richness decreased with stream order increase. (3) Shannon-Wiener diversity, Simpson dominance and Pielou uniformity showed significant difference with stream orders; Shannon-Wiener diversity rose firstly then dropped afterwards. Further analysis showed that stream orders had a significant impact on riparian habitats, riparian vegetation and disturbances. This meant that riparian vegetation experienced different types and degrees of disturbance in different stream orders, so the Hierarchical Management Strategy(HMS) should be applied to riparian vegetation management.4. Based on the methods of TWINSPAN and DCCA, this paper studied the ecological gradients of the plant communities in Donghe River, in terms of the interactions between plant species and communities and environmental factors. The results showed that: (1) Based on TWINSPAN, 42 sites were classified into 15 associations, of which, 4 associations were forest communities, 11 were shrubs and herbs. All of the associations appeared the characteristic of secondary vegetation types, represented the different human disturbance intensity. (2) DCCA ordination revealed the relationships between the distribution patterns of the plant communities and the environmental components (altitude, riparian slope, aspect, riparian width, substrate type, substrate heterogeneity, stream width, stream order and human disturbance). The dominant factors controlling the distribution patterns of the plant communities were altitude and human disturbance, while riparian width, river width and stream order also had effects on the community characteristics. (3) Combined the correlations among environment factors with the results of the DCCA ordination, the most important factor affecting plant distribution in riparian zone was altitude, which was followed by human disturbance, riparian width, river width and stream order. Synthesize the results of TWINSPAN and DCCA, the riparian plant communities showed the following characteristics: along the elevation gradient, plant communities had significant altitudinal gradient; along longitudinal and lateral gradients of river, pattern of plant communities presented'fragmentation'. The composition and types reflected that the riparian plant communities were typical secondary plant communities.5. The effects of hydropower development on riparian vegetation were studied along along upstream and downstream reaches of three hydropower reservoirs on the Baili River, Xiaoyuan River, and Manyue River. The results showed that: (1) 125 plant species in a total of 216 quadrats were recorded, with 4 trees, 30 shrubs and 71 herbs. (2) There were significant differences on plant communities (species richness, species cover) amongst rivers, the upstream versus downstream, with amongst rivers had larger differences. This suggested that the dams had led to changes in riparian plant communities, but difference caused by reservoir was within the natural range of variation found across the rivers. (3) We found some xerophytes and highland plants significant increased downstream of dams, such as Cupressus funebr, and some adaptation to tranquil reaches and lakes species significant increased upstream of dams, such as Azolla imbircata, Polygonum nepalense. This revealed that the construction of dams had changed the riparian habitat and the composition and diversity of riparian plant between downstream and upstream of dams.6. In order to understand the spatial pattern of plant community and the maintenance mechanism of biodiversity in littoral zone of Three Gorges Reservoir, 110 km stretches of Pengxihe River (from estuary to the backwater of Three Gorges) were chose to study. We investigated species composition and environmental variables along 50 m long stretches of riverbank between the high-water level and the lowest summer water level, with a 5 km interval. The results showed that: (1) along longitudinal gradients, longitudinal species richness, longitudinal shrub species richness and longitudinal herb species richness were significantly related to distance to estuary; (2) along lateral gradient, there were visible different changes in all kinds of types (lateral species richness, lateral tree species richness, lateral shrub species richness, lateral herb species richness).Along lateral gradient, species richness and herb species richness increased with the elevation then reduced, trees and shrubs species richness increased with the elevation. (3) Correlation analyses showed that substrate types were correlated with the longitudinal species richness, without considering the distance to estuary. Soil moisture and substrate heterogeneity were correlated with lateral, species richness. These results indicated that, along longitudinal gradient of the river, distance to estuary played an important role in species richness, while along lateral gradient spatial heterogeneity due to inundation and flooding played an important role in forming a new pattern of plant community in the littoral zone of Three Gorges Reservoir Region. Because of special hydrological dynamics, plant in the littoral zone of Three Gorges are gradually form a unique spatial pattern to some extent, although it had the same change law with riparian plant of a natural river.7. In order to find out the relationship between riparian communities and soil properties in Three Gorges Reservoir after its initiate impounding to 173 m height, plant community was investigated in the riparian of Baijiaxi Stream. Based on field survey and laboratory experiment, plant diversity and soil properties were studied. The results showed that: (1) Riparian zone was divided into five habitats with different heights, which well reflected the water level changes from 145 m to 175 m. Between 155 m to 160 m, results showed the highest species richness and Shannon-Wiener diversity, with the lowest appeared at less than 150 m area. (2) Among different habitats, soil properties showed significant differences. (3) Correlation analysis showed that the species richness and Shanon-Wiener diversity index was influenced by soil heterogeneity, soil type, soil moisture, soil available potassium.