Research On Plant Community Succession And Dynamics Of Vegetation During Last 30 Years In Modern Yellow River Delta Based On RS And GIS Techniques

The modern Yellow River Delta is located at the mouth of the Yellow River flowing to the sea, north of Shandong Province, China. Its area is about 2200km~2 . This region is also a transition zone from sea to terrestrial land, and is land-and-water interlock zone too. Affected by several factors such as tail channel fluctuation , seacoast erosion, river mouth deposit, plant succession, soil development, human reclamation and activities, its ecological environment is very fragile. It shows distinct characters of wetland ecosystem, and is the youngest, largest, most integrated reserve new-born wetland ecosystem of river mouth in the warm and temperate zone of China.It is the most frequent change region from sea to land in our country or the large river in the world. The modern Yellow River Delta is the youngest land created by the yellow river, the most frequent change for its flow path to the sea, and the most dynamic area for vegetation succession. It is the ideal region for studying plant succession, and its research achievements are of typicality and uniqueness.This study is basic work for vegetation research of Yellow River Delta, therefore, the study is of an important significance for future study of dynamical characteristics, vegetation classification and regionalization, ecological restoration and reconstruction in delta area.Using "3S"(RS, GIS and GPS) techniques, dynamics of vegetation in modern Yellow River Delta were studied, which is important part for systematic studies on dynamics of vegetation in the region. It is of applied value for digital construction , resource exploitation and protection of Yellow River Delta.The natural succession of plant community in modern Yellow River Delta belonged to primary succession without human disturbance. The succession series of plant community in the study area was as follows: saline bare land→community Suaeda salsa→community Tamarix chinensis→Grassland. The formation of this succession series was closely related to soil water and salt dynamics. Soil near coastline, which has higher salt content, was bare land, going up from bare land, salt-enduring species Suaeda salsa and Tamarix chinensis occurred. These two species formed monodominant community or community consisting of both of them. With distance from coastline increasing, rising of altitude and decreasing of soil salt content, the importance of Suaeda salsa and Tamarix chinensis became lower, the component of perennial grass dominated gradually. The community types dominated by Phragmites australis, Imperata cylindrica and Aeluropus littoralis were developed in suitable area. These community types were the higher stage of natural succession in modern Yellow River Delta.Data were collected in different successional stages using a simultaneous sampling method and analyzed through quantitative classification method. Three large groups and 12 classes were made to represent the community patterns of three succession stages and 12 succession communities. The three succession stages were as follows. Saline bare land→Community Suaeda salsa→Community Tamarix chinensis→Grassland. 12 succession communities were respectively: community Suaeda salsa, Community Suaeda salsa + Phragmites australis, Community Tamarix chinensis, Community Tamarix chinensis + Suaeda salsa, Community Tamarix chinensis + Suaeda salsa + Phragmites australis ,Community Tamarix chinensis + Suaeda salsa + Limonium sinesis, Community Phragmites australis + Suaeda salsa + Apocynum venetum, Community Phragmites australis+Cynanchum chinensis + Artemisia capillaries, Community Echinochloa littoralis + Ixeris chinensis + Phragmites australis, Community Phragmites australis + Glycine soja, Community Imperata cylindrica + Glycine soja, Community Aeluropus Littoralis + Phragmites australis + Suaeda salsa. Succession degree of 12 communities were calculated. Most of these communities were in the lower succession stage, their succession degree were between 30 and 184.3. However, Community Phragmites australis + Glycine soja and community Imperata cylindrica + Phragmites australis were close to the succession stage of grassland climax, their succession degree were 286.9 and 230.7 respectively. Heterogeneity index and richness index increased gradually during the community succession process, but species evenness tended to decrease with succession development.The relation between succession and environment was studied by ordination technique, and the results showed that the soil salt content was an important factor to halarch succession of modern Yellow River Delta. It affected community structure, species composition and succession process.Based on landsat TM image in 1987,1996,2004 and MSS image in 1977,vegetation cover changes about 30 years in modern Yellow River Delta were studied by using the normalized difference vegetation index (NDVI), and vegetation coverage was classified. The results are as follows: During 27 years, vegetation cover area was tend to increase, and total increased area of vegetation was 91089.43 hm~2, with an average increase of 3373.68 hm~2 per year. 34.71% has increased to vegetation cover rate, with an average increase of 1.29% per year. Vegetation in study area was main in lower coverage, vegetation in higher coverage was minor, but area of vegetation in higher coverage was increased yearly, with an average increase of 412.83 hm per year.Three kinds of wetland, including river, marsh and seabeach, existed in early years during the study, and reservoir, paddy field, prawn pool and pond were added to the wetland in late years. Affected by the flow of Yellow River and the activities of human, the area of river and marsh tended to decrease, the area of river and marsh had respectively decreased 15085hm~2 andl5085hm~2, however, the area of reservoir, paddy field, prawn pool and seabeach increased obviously, its area had respectively decreased 1790hm~2,1225hm~2,7713hm~2 and 25970hm~2.Interpretation of vegetation in the studied region was conducted, the results are as follows: the area of vegetation for Phragmites australis was increased in general, its area had increased 314.09 hm~2. Vegetation area of Tamarix chinesis, Suaeda salsa and cropland appeared increasing tendency, their area had increased 1066.14 ,1128.87 and 5811.71 hm~2 respectively. Area of woodland Robinia pseudoacacia was fluctuated. its area had increased 1674.81 hm~2 from 1987 to 1996, and appeared decreasing tendency from 1996 to 2004, its area had decreased 709.65 hm~2 .Dynamic zone of vegetation succession concentrated mainly in north, east region near seacoast and new region deposited by the Yellow River in southeast. Vegetation distribution line in north shortened 6.3 km in largest, total vegetation area eroded by sea was 29309.06 hm~2 from 1977 to 1996. After 1996, due to construction of coast engineering, coast line in north and east was relative stable, vegetation erosion was checked. New deposited region in southeast, due to plentiful fresh water and better soil condition, plant invaded soon into the region. Vegetation in the area distributed around the Yellow River shore, increased area of vegetation in southeast was 40592.34 hm~2 from 1977 to 1987, 26027.14 hm~2 from 1987 to 1996, 31310.31 hm~2 from 1996 to 2004.The soil salt content was the main factor that affected vegetation distribution of the Yellow River Delta. The species of Tamarix chinesis and Suaeda salsa distributed in the area that contained higher soil salt content. The species of Phragmites australis distributed in the area with plentiful fresh water around the Yellow River shore, the old course of the Yellow River and reservoir. However, woodland Robinia pseudoacacia was concentrated in area with high ground level and desalted fully soil around the old course of the Yellow River and north shore of the Yellow River.