The Relationship Between Vegetation Distribution And Environmental Factors

The study of vegetation distribution is the highlight of plant ecology. Since the simple vegetation structure and obvious environmental gradient of wetlands, they have become ideal places for ecologists to study the relationship between vegetation and environment factors. Recently, with the intensive human activities and global change, the area of wetlands is declining. It is important for us to derive the key environmental factors that control the wetland vegetation distribution and succession, so as to protect and restore wetlands more successfully.This study was carried out in the East Head Land of Chongming Island, Shanghai, with special focus on the reed community and its neighboring vegetation types. We investigated the abundance of different species according to the quadrats and the environmental factors along transects across vegetation boundaries. Based on the methods of ANOVA, PCA and CCA, the following results were obtained:1. No significant difference of soil total organic matter and total nitrogen was detected among bare flats, Phragmites australis zone and Spartina alterniflora zone. It is also the same case for water-table depth. The elevation of bare flat, Phragmites zone and Spartina zone show no obvious difference at high and low marsh, while Spartina zone had the highest salinity. The median grain size of soil in the high marsh is smaller than that in the low marsh. In the high marsh, the compactness of the bare flat is higher than that in the vegetated area.2. The first six principal components extracted from PCA can explain 95.5% of the total variance. The first principal component can explain 43.3% of the total environmental variance. The median grain size (D50) has the highest weight in the first principal component.3. Soil salinity and grain size increase from Carex zone to Phragmites zone, and then Spartina zone. Elevation has opposite trends among the three vegetation zones. The pH of Phragmites zone is higher than that of the Spartina zone and Carex zone. Meanwhile, the Spartina zone has the highest nutrient content.4. The result of canonical correspondence analysis shows that the median grain size of the soil is the most affective factor of vegetation density in Chongming East Head Land, the second one is soil salinity.