Zonation of plant cover and environmental factors in wetlands of the Sanjiang Plain, northeast China

The zonation of depressional and riparian wetlands in the Sanjiang Plain of northeastern China was studied to describe their vegetation composition and environmental variables. We sampled 108 plots in 6 depression and riparian wetlands. Samples were classified into 4 groups using two-way indicator species analysis (TWINSPAN). Emergent marsh vegetation was characterized by Carex lasiocarpa and C. pseudocuraica, meadow marsh vegetation by tussock species such as Carex appendiculata and C. meyeriana, wet meadow vegetation by Calamangrostis angustifolia and Carex appendiculata, and shrub meadow vegetation by the shrubs Betula fruticosa, Alnus sibirica and Salix rosmarinifolia and the graminids Carex schmidtii and Calamagrostis angustifolia. CCA ordination showed that water table, organic matter and available N were the major factors explaining the vegetation zonation pattern. Compared with other Northern Hemisphere regions, bog and fen vegetation are completely absent due to climatic conditions unfavorable for peat formation. Out of four vegetation types, only the Carex lasiocarpa community and the C. pseudo-curaica community have been found in other regions. However, at the species level many species are widespread and some species are vicariant or pseudovicariant to other regions in the world. Our study suggests that topography and hydrology may be the most important determinants of the vegetation pattern in this region.