The Effects Of Land Use On Herbaceous Community Structure In The Riparian Zone

The riparian zone is an important geographical element in the landscape of the river basin. And it is the important link between the river ecosystem and the terrestrial ecosystem. The riparian zone is located in the junction of land and water, has obvious edge effect, and provides habitat for all kinds of creatures, and has a high biodiversity. Along with the development of agriculture and urbanization, and the influence of human disturbance, the vegetation community structure of riparian zone, especially herbaceous plant have disappeared and degraded obviously. The land use and the riparian biodiversity pattern were closely related. The study on the plant community structure and its influencing factors under human activities are helpful to the further understanding of the disturbance degree of human activities on the riparian ecosystem in order to provide theoretical basis for the protection and management of plant community structure in the riparian ecosystem.This study set plots in herbaceous plant community in different land use types (including forest land, farmland, village and town) of rivers belonging to the Taihu basin in 2014,2012, respectively and carried out the following investigations. In the three different periods in January 2014 (winter) and April (spring) and August (summer), in the investigation plots, seed was collected. We used the similarity analysis between the aboveground vegetations and soil seed bank to investigate the influence of the soil seed bank on riparian plant community structure. We tried to understand the effects of the environmental factors on the community structure of herbal plants through the correlation between the riparian vegetation diversity and the environmental factors. The main conclusions are as follows:(1) There were 25 families,48 genera and 57 species and Gramineae, Compositae were the dominant genera in three different land use types. The number of species of herbaceous plant under different land use was different, as the main performance was village (44)> farmland (34)> forest land (33).(2) A follow up investigation of ground flora had been made in 2012 and 2014.The common species between 2012 and 2014 only took up only 58% and 53% of the total species respectively. There were only 29 species in these two years.A portion of existed species in 2012 had been disappeared and replaced by novel species in 2014. Under three different land use,there were 8 herbaceous plants remained the same. Plant species would vary in the number and structure due to different land use.(3) Research of riparian seasonal variation of soil seed bank in different land use types had been investigated. The results showed that a total of 59 species (belonging to 21 families,54 genera of herbaceous plants) had sprouted in three seasons. Annual gramineae species occupied an important portion which was 64% of the total, and perennial plants took up 19%. From the species composition, the germination numbers of winter, spring and summer were 33,44 and 40 respectively. The soil seed bank of riparian zone was more abundant than that of above ground vegetation. The maximum reserves of 21532.9±8798.9 grain/m2 occur in the spring of farmland. At the same time, forest species diversity was higher than that of farmland and villages because of weak human disturbance. Forest biodiversity was significantly lower than that of farmland and towns in the spring and summer.(4) Analysis of the seasonal variation of riparian soil seed bank under different types of land use had been made. Results showed that seeds were distributed differently in the 0～15cm soil layer. Soil seed bank reserves, species composition and species diversity would decrease with the depth of the soil.Under different disturbance situation in different seasons, soil seed bank in farmlands and towns would change differently. Seeds were usually found in the deeper soil in severe seasonal disturbance.(5) The common plants species were 38 between riparian soil seed bank and above vegetation species.There were 21 plants species which were only occurred in soil seed ban and 17 which was in aboveground.The similarity coefficient between the soil seed bank species and above ground plant species was 0.667.The similartity between soil seed bank and riparian vegetation was centrally over 60% -80% for different land use types and life forms which was high given the circumstances.(6) A simulation model of the response of riparian herbaceous plants community structureto the environmental factors had been done. Results showed that land use types soil pH and slope aspect were influencing factors on plants diversity. Diversity of sunny slope was higher than shady slope; pH in woodland in downstream was a little high and the plants diversity remained medium, while pH of farmland was the lowest of all and the diversity was the least. Seed would move to downstream because of the water flows which leads to the higher diversity of plants in woodland of downstream. There was siginificant difference between rivers of village land use which might be the results of human disturbances.