Long-term changes in marsh vegetation in Sanjiang Plain, northeast China

QuestionsIs there a consistent change in species composition and species richness across the communities along the wetness zonation? Which species are sensitive to environmental changes? Has species richness increased or decreased? What are the relative effects of climate, geographical position and local environmental factors on the inland marsh community? LocationSanjiang Plain, northeast China (130-133 degrees E, 45-48 degrees N). MethodsA total of 94 plots were re-surveyed in 2012 and compared with data from 1973. Detrended correspondence analysis (DCA) and indicator species analysis were used to analyse the direction and nature of change in community composition between 1973 and 2012. Paired t-test was used to test for change in species richness, water level and soil variables between the two surveys. Correlation and step-wise regression analyses were used to test the relationship between vegetation change (species richness and DCA scores), environmental variables and geographic position. ResultsVegetation has changed towards a drier state, with the greatest changes in the wettest Carex lasiocarpa community and the smallest changes in the driest Calamagrostis angustifolia community. The frequency and cover of hygrophilous species and species typical of oligotrophic wetlands decreased, while grasses and other non-marsh species increased. Species richness per community and per plot increased over time. The dynamics within each community was only weakly correlated with biogeographic predictors: longitude, latitude, elevation and annual precipitation. ConclusionsHydrology was the main factor controlling changes along the marsh zonation, and was most likely in response to climate warming and land-use changes. The different responses among the marsh communities along the zonation and between hydrophytes and other species imply that future protection and management need to be based on community type and plant functional types.